SlideShare ist ein Scribd-Unternehmen logo
1 von 56
Downloaden Sie, um offline zu lesen
Spectroscopy
Spectroscopy
               MASS SPECTROSCOPY




                       -: Presented By :-
                       Amruta S. Sambarekar
                       1st Year M.Pharm
                       Dept. of Pharmaceutics
                       M M C P, BELGAUM.
                                          1
Spectroscopy
Spectroscopy
                                Contents
                Introduction
                Basic principle
                Theory
                Brief outline of instrumentation.
                Ion formation and types
                Fragmentation processes
                Fragmentation patterns
                Fragmentation characteristics in relation to
                 parent structure and functional groups
                                                                2
Spectroscopy
Spectroscopy
                             Mass spectroscopy
               Mass spectroscopy is one of the primary spectroscopic
               methods for molecular analysis available to organic chemist.

               It is a microanalytical technique requiring only a few
               nanomoles of the sample to obtain characteristic information
               pertaining to the structure and molecular weight of analyte.

               It is not concerned with non- destructive interaction between
               molecules and electromagnetic radiation.



                                                                      3
Spectroscopy
Spectroscopy
               It involves the production and separation of ionised molecules
               and their ionic decompositon product and finally the
               measurement of the relative abundance of different ions
               produced. It is, thus a destructive technique in that the sample is
               consumed during analysis.

               In most cases, the nascent molecular ion of the analyte
               produced fragment ions by cleavage of the bond and the resulting
               fragmentation pattern constitutes the mass spectrum.

               Thus, the mass spectrum of each compound is unique and can
               be used as a “chemical fingerprint” to characterize the sample.




                                                                            4
Spectroscopy
                               Basic principle
Spectroscopy

               Mass spectroscopy is the most accurate method for
               determining the molecular mass of the compound and its
               elemental composition.

               In this technique, molecules are bombarded with a beam of
               energetic electrons.

               The molecules are ionised and broken up into many fragments,
               some of which are positive ions.

               Each kind of ion has a particular ratio of mass to charge, i.e.
               m/e ratio(value). For most ions, the charge is one and thus, m/e
               ratio is simply the molecular mass of the ion.

                                                                          5
Spectroscopy
Spectroscopy
               Mass spectra is used in two general ways:

                 1) To prove the identity of two compounds.

                 2) To establish the structure of a new a compound.

               The mass spectrum of a compound helps to establish
                the structure of a new compound in several different
                ways:

                 1) It can give the exact molecular mass.

                 2) It can give a molecular formula or it can reveal the
                    presence of certain structural units in a molecule.

                                                                           6
Spectroscopy
Spectroscopy
                                   Basic theory
                Mass spectroscopy deals with the examination of the
                 characteristics fragments(ions) arising from the
                 breakdown of organic molecules.

               A mass spectrum is the plot of relative abundance of
                ions against their mass/charge ratio.

               The basic aspect of organic mass spectrometry consist of
                bombarding the vapour of an organic compound with a
                beam of energetic electron accelarated from a filament to
                an energy of 70 eV to form positively charged ions
                (molecular ions).


                                                                            7
Spectroscopy
Spectroscopy
                The additional energy of the elecrons is dissipated in breaking
               the bonds in the molecular ion, which undergoes fragmentation to
               yield several neutral or positively charged species.

               This fragmentation may result in the formation of an even-
               electron ion and radical.

               The various positive ions, thus formed, can be accelerated and
               deflected by magnetic or electric fields.

               The deflection of ions, however, depends on its mass, charge
               and velocity.

                                                                           8
Spectroscopy
Spectroscopy
                For a given charge, velocity and deflecting force, the
               deflection is less for a heavy particle as compared to that of a
               light one.

               Thus, a number of beams each containing ions with the same
               m/z values are obtained.

               These beams are then made to strike against a photographic
               plate where not only they appear as separate lines but the
               intensity of each peak is also recorded.

               The clear visual presentation of a mass spectum is usually
               obtain by plotting m/z value against relative abundance,
               assigning the most abundant ion (base peak)in the spectrum as
               100 per cent.
                                                                        9
Spectroscopy
Spectroscopy
                Though organic mass spectrometry is routinely used along
               with IR, NMR and UV for structure detemination, its basic
               theory is different from the others.

                In mass spectrometry no characteristic selective absorption of
               radiation is involved as in the case of the other three methods,
               secondly, in the mass spectrometry, the compound undergoes
               irriversible chemical changes unlike in the others, where the
               changes are reversible physical changes.

               The mass spectral reactions are much more drastic than usual
               chemical reactions.


                                                                          10
Spectroscopy
Spectroscopy   Principle and Instrumentation




                                               11
Ionisation
Spectroscopy
Spectroscopy
               The atom is ionised by knocking one or more electrons
               off to give a positive ion. (Mass spectrometers always
               work with positive ions).




               The particles in the sample (atoms or molecules) are
               bombarded with a stream of electrons to knock one or more
               electrons out of the sample particles to make positive ions.
                                                                       12
Spectroscopy
Spectroscopy

               Most of the positive ions formed will carry a charge
                of +1.

               These positive ions are persuaded out into the rest of the
               machine by the ion repeller which is another metal plate
               carrying a slight positive charge.




                                                                   13
 Acceleration
Spectroscopy
Spectroscopy
                The ions are accelerated so that they all have the
               same kinetic energy.




                                                                      14
Spectroscopy
Spectroscopy

               The positive ions are repelled away from the positive
               ionisation chamber and pass through three slits with voltage
               in the decreasing order.

               The middle slit carries some intermediate voltage and the
               final at ‘0’ volts.

               All the ions are accelerated into a finely focused beam.




                                                                    15
Spectroscopy
Spectroscopy
                Deflection
               The ions are then deflected by a magnetic field
               according to their masses. The lighter they are, the
               more they are deflected.

               The amount of deflection also depends on the
               number of positive charges on the ion -The more the
               ion is charged, the more it gets deflected.




                                                                      16
Spectroscopy
Spectroscopy
               Different ions are deflected by the magnetic field by
               different amounts. The amount of deflection depends
               on:

               The mass of the ion: Lighter ions are deflected more
               than heavier ones.

               The charge on the ion: Ions with 2 (or more)
               positive charges are deflected more than ones with only
               1 positive charge.



                                                                 17
 Detection
Spectroscopy
Spectroscopy
               The beam of ions passing through the machine is detected
               electrically.

                                              Only ion stream B makes it right through the machine to
                                              the ion detector.

                                              The other ions collide with the walls where they will
                                              pick up electrons and be neutralised.

                                              They get removed from the mass spectrometer by the
                                              vacuum pump.




               When an ion hits the metal box, its charge is neutralised
               by an electron jumping from the metal on to the ion.
                                                                    18
Spectroscopy
Spectroscopy

               That leaves a space amongst the electrons in the
               metal, and the electrons in the wire shuffle along to fill
               it.

               A flow of electrons in the wire is detected as an
               electric current which can be amplified and recorded.
               The more ions arriving, the greater the current.




                                                                     19
Spectroscopy
Spectroscopy
                  Fragmentation process:
                   
                  Bombardment of molecules by an electron beam with
               energy between 10-15ev usually results in the ionization of
               molecules by removal of one electron (Molecular ion
               formation).

                   When the energy of electron beam is increased
               between 50-70ev, these molecular ions acquire a high
               excitation resulting in their break down into various
               fragments. This process is called “ Fragmentation process”.



                                                                    20
Spectroscopy
Spectroscopy
                    Types of Ions:

                
               1. Molecular ion or Parent ion.
               2. Fragment ions.
               3. Rearrangement ions.
               4. Multicharged ions.
               5. Negative ions.
               6. Metastable ions.



                                                 21
Spectroscopy
Spectroscopy
               1. Molecular ion or Parent ion:
                  When a molecule is bombarded with electrons in
                   high vacuum in Mass spectrometer, it is converted into
                  positive ions by loss of an electron. These ions are
                  called as Molecular or Parent ions.
                  M + e → M+° + 2e—
                  Where,
                  M – represents the Molecule;
                  M+°– represents the Molecular or Parent ion
                  The order of energy required to remove electron is
                  as follows—

                  σ electrons > non-conjugated π > conjugated π >
                  non bonding or lone pair of electrons.

                                                                    22
Spectroscopy
Spectroscopy
                      Many of these molecular ions (M+°) disintegrate at
                      10-10 to 10-13 seconds to give a positively charged
                     fragment and a radical in the simplest case. If some
                      Molecular ions remain intact long enough (about
                   10-6 seconds) to reach the detector.

                     Most molecules show a peak for the molecular ion, the
                   stability of which is usually in the order—
                   Aromatic > Conjugated acyclic polyenes > Alicyclics > n-
                   hydrocarbons > ketones > ethers> Branched chain
                   hydrocarbons > Alcohols.

                                                                     23
Spectroscopy
Spectroscopy
               Characteristics of Molecular ion:

               Molecular peak is observed if molecular ion remains intact
               long enough (10-6 seconds) to reach the detector. This peak
               gives the molecular weight of the compound. The
               molecular ion peak is usually the peak of the “highest
               mass number.”

               The molecular ion M+° has mass, corresponding to the
               molecular weight of the compound from which it is
               generated. Thus the mass of a Molecular ion M+° is an
               important parameter in the identification of the compound.


                                                                     24
Spectroscopy
Spectroscopy   Significance of Molecular ion:
                Molecular ion peak gives the molecular weight of the
                compound.
                i.e. m/z of molecular ion = molecular weight of the compound.
                Ex: C2H5+ (m/e=29) gives the molecular weight of Ethane.
               2. Fragment ions:
                  When the energy is given to Molecular ion during electron
                 impact, further cleavage takes place and ions of lower mass
                 number known as Fragment ions are produced.
                                    M+° → M+1 + M2
                           +°      +
                  Ex: CH3OH → CH2OH


               3.Rearrangement ions:
                         m/z 32 m/z 31

                   Rearrangement ions are the fragments whose origin
                 cannot be described by simple cleavage of bonds in the
                 parent ion, but are result of intramolecular atomic
                 rearrangement during fragmentation.                 25
These are probably due to recombination of fragment ions and
Spectroscopy
Spectroscopy
                known as rearrangement peaks.
                 Ex: Prominent peak in spectrum of diethyl ether occurs at m/e 31.
                 This is due to the ions CH3O+, which is formed by rearrangement
                 of C2H5O+ ions.
               4. Multi charged ions:
                  Some times ions may also exist with two or three charges instead of
                 usual single charge in the mass spectrum. These are known as
                 doubly or triply charged ions. They are created as follows:
                  M+° + e- → M++ + 3e-
                 But under normal operating conditions, most of the ions produced
                 are single charged. The doubly or triply charged ions are recorded at
                 a half or one third of the m/e value of the single charged ions.
                 Formation of these multiple charged ions is more common in hetero
                 aromatic compounds. They are also common in inorganic mass
                 spectrum. Gases such as CO, N2,CO2 and O2 have measurable peaks
                 corresponding to CO+2,N+2,and O+2.
                                                                                  26
Spectroscopy
Spectroscopy   5. Negative ions: The positive ions predominate in electronic
                 impact ionization because of greater stability. The Negative ions are
                 not very useful in structural determinations. The formation of
                 Negative ions is very rare but these can be produced in three ways:
                                 1.AB + e → A+ + B—
                                  2.AB + e → AB—
                                  3. AB + e → A+ + B— + e—


               6. Metastable Ions: Fragment of a parent ion will give rise to a
                 new ion (daughter) plus either a neutral molecule or a radical.
                             M1+       M2+ + non charged particle
                 An intermediate situation is possible; M1+ may decompose to
                 M2+ while being accelerated. The resultant daughter ion M2+
                 will not be recorded at either M1 or M2, but at a position M* as
                 a rather broad, poorly focused peak. Such an ion is called a
                 metastable ion.
                                                                                    27
28
Spectroscopy
Spectroscopy
Nature Of Metastable Ions:
Spectroscopy
Spectroscopy
                      Metastable ions have lower kinetic energy than normal
               ions and metastable peaks are smaller than the M1 and M2
               peaks and also broader. These metastable ions arise from
               fragmentation that takes place during the flight down through
               ion rather than in the ionization chamber.

               Molecular ions formed in the ionization chamber do one of
                   the following things:
               1. Either they decompose completely and very rapidly in
                   the ion source and never reach the collector (as in case
                   of highly branched molecular ions with life times less
                   than 10-5 seconds).
               2. Or else they survive long enough to reach the collector
                   and be recorded there (life times longer than 10-5).
                                                                        29
Spectroscopy
Spectroscopy
               Significance of Metastable ions:

               Metastable ions are useful in helping to establish fragments
               routes.

               Metastable ion peak can also be used to distinguish between
               fragmentation Processes, which occur in few microseconds.




                                                                      30
Spectroscopy
Spectroscopy
                     General rules for fragmentation:
               1. The relative height of the molecular ion peak is greatest for the
                  straight chain compound and decreases as the degree of
                  branching increases.

               2. The relative height of the Molecular ion peak usually
                 decreases with increasing molecular weight in a
                  homologous series.

               3. Cleavage is favoured at alkyl substituted carbon atoms;
                 the more substituted, the more likely is cleavage. This is a
                 consequence of the increased stability of a tertiary carbon
                 atom over a secondary, which in turn is more stable than
                 a primary.
                            CH3+ < RCH2+ < R2CH+ < R3C+
                                                                       31
STEVENSONS RULE:
Spectroscopy
Spectroscopy
                When an ion fragments, the positive charge will remain on the
                fragment of lowest ionization potential.
                Generally the largest substituent at a branch is eliminated most readily
                as a radical, presumably because a long chain radical can achieve some
                stability by delocalization of the lone electron.
                Ex- cleavage of 1-methyl pentane



                           1-methyl pentane         largest fragment

                                        In this fragmentation, positive charge remains
                on the more high substituted fragments, i.e. the one with lower
                ionization potential.
               4. Double bonds, cyclic structures and especially aromatic or
                  hetero aromatic rings stabilize the Molecular ion and thus
                  increase the probability of its appearance.           32
Spectroscopy   5. Double bonds favour allylic cleavage and give the
Spectroscopy
               resonance stabilized allylic carbonium.
               Ex: Mass spectrum of 1-butene




               6. Saturated rings tend to lose alkyl side chains at the α
                  carbon atom. This positive charge tends to stay with the
                  ring fragment.
               Ex: Mass spectrum of n-propyl cyclohexene




                                                                      33
Spectroscopy
Spectroscopy
               7. In alkyl substituted aromatic compounds, cleavage is very
               probable at the bond β to the ring, giving the resonance stabilized
               benzyl ion or more likely, the tropylium ion:
               Ex: mass spectra of n-butyl benzene.




               8. Cleavage is often associated with elimination of small,
                  stable, neutral molecules such as carbon monoxide,
                  olefins, water, ammonia, hydrogen sulphide, hydrogen
                  cyanide, mercaptans, ketone, or alcohols, often with
                  rearrangement.
                                                                     34
Spectroscopy
Spectroscopy

               Factors influencing Fragmentation process:

               1.     Bombardment energies

               2.     Functional groups

               3.     Thermal decomposition




                                                            35
Spectroscopy
Spectroscopy
                     General modes of fragmentation:

               Fragmentation of the molecular ion takes place in following
                  modes:
               * Simple cleavage
               1. Homolytic cleavage
               2. Heterolytic cleavage
               3. Retro Diels-Alder reaction
               * Rearrangement reactions accompanied by transfer of atoms.
               1. Scrambling
               2. Mc Lafferty rearrangement
               3. Elimination
                                                                       36
Spectroscopy
Spectroscopy
                1. Homolytic cleavage :

                Here fragmentation is due to electron redistribution between
                 bonds.

                R ─ CH2 ─ CH2 ─ R'            R ─ CH2 : CH2 ─ Rꞌ


                                                       e-




                                           R ─ CH2+. + CH2 ─ R'



                                                                          37
Spectroscopy
Spectroscopy   2. Heterolytic cleavage:
               Fragmentation by movement of two electrons:
               In this type of cleavage both the electrons of the bond are taken
               over by one of the atoms; the fragments are an even electron
               cation and a radical with the positive charge residing on the
               alkyl group. It is designated by a conventional arrow (↶ or ↷) to
               signify the transfer of a pair of electrons in the direction of the
               charged site.




               3. Retro Diels-Alder reaction:
               Elimination by multiple σ bond rupture:
               cyclohexene is broken down to Diene and Dienophile. It can
                  be explained by one or two electron mechanism.
                                                                       38
Spectroscopy
Spectroscopy
               One electron mechanism:



               Two electron mechanism:


               * Rearrangement reactions accompanied by transfer of
                  atoms:
               1. Scrambling:
               Fragmentation giving rise to stable carbocation:
               In certain cases fragmentation takes place at bond, which
                  gives stable carbocation.
               Ex- Molecular ion from the alkyl benzene undergoes
                  fragmentation at the benzylic bond and final product is
                  seven membered cyclic ion known as Tropylium ion. 39
Spectroscopy
Spectroscopy


               2. Mc Lafferty rearrangement:
               Fragmentation due to rearrangement of Molecular or Parent ion:
               Here cleavage of bonds in Molecular ion is due to the intramolecular
               atomic rearrangement. This leads to fragmentation whose origin
               cannot be described by simple cleavage of bonds. When fragments
               are accompanied by bond formation as well as bond for breaking, a
               rearrangement process is said to have occurred.


               Such rearrangement involves the transfer of hydrogen from one part
               of the molecular ion to another via, preferably, a six-membered
               cyclic transition state. This process is favoured energetically because
               as many bonds are formed as are broken.
                                                                                  40
Spectroscopy   Compounds containing hydrogen atom at position gamma to
Spectroscopy
               carbonyl group have been found to a relative intense peak. This is
               probably due to rearrangement and fragmentation is accompanied
               by the loss of neutral molecule. This rearrangement is known as
               McLafferty rearrangement.

               The rearrangement results in the formation of charged enols and
               a neutral olefins.




               To undergo McLafferty rearrangement, a molecule must posses
               a. An appropriately located heteroatom (ex.oxygen)
               b. A double bond
               c. An abstractable Hydrogen atom which is γ (gamma) to
                  C=Osystem.                                            41
Spectroscopy
Spectroscopy
               Table for the common McLafferty peak in the spectra of carbonyl group.


                            Compound type          Substituent          McL peak
                                                      (R)
                                 Aldehyde               -H                   44



                               Methyl ketone           -CH3                  58



                                  Amide                -NH2                  59



                                   Acid                 -OH                  60



                               Ethyl ketone           -CH2CH3                72



                               Methyl ester            -OCH3                 74




                                                                                        42
Spectroscopy
Spectroscopy   3. Elimination:
                Fragmentation due to loss of small molecule:
               Loss of small stable molecules such as H2O, CO2, CO,C2H4 from
               molecular ion during fragmentation.
               Ex- An alcohol readily looses H2O molecule and shows a peak 18
               mass units less than the peak of molecular ion.



                Fragmentation adjacent to the branching point:
               In case of branched alkanes, bond fission takes place adjacent to
               the branching point. Hence this leads to the formation of more
               stable carbocation
               Ex: 3-methyl pentane

                                                                        43
Spectroscopy
Spectroscopy
                FRAGMENTATION PATTERNS AND FRAGMENTATION CHARACTERISTIC
                   RELATION TO PARENT STRUCTURE AND FUNCTIONAL GROUPS:



               1. Saturated Hydrocarbons-
               a. Straight chain compounds: Following are the features of the mass
                 spectra of Alkanes.
                The relative height of the parent peak decreases as the molecular
                 mass increases in the homologous series.
                The Molecular ion peak (although weak) is normally present.
                The spectra generally consist of clusters of peaks separated by 14
                 mass units corresponding to differences of CH2 groups.
                The largest peak in each cluster represents CnH2n+1 fragment. This is
                 accompanied by CnH2n and CnH2n-1 fragment corresponding to the loss
                 of one and two H atoms respectively.
                                                                                44
Spectroscopy
Spectroscopy
               b. Branched Chain Hydro Carbons:
                Greater the branching in Alkanes less is the appearance of the
                  molecular ion and if it appears, intensity will be low.
                Bond cleavage takes place preferably at the site of branching.
                  Due to such cleavage, more stable secondary or tertiary
                  carbonium ions results.
                Generally, largest substituent at a branch is eliminated readily
                  as a radical. The radical achieves stability by the de-
                  localization of lone electron.
                Greater number of fragments results from the branched chain
                  compound compared to the straight compound. This is due to
                  greater pathways available for cleavage.




                                                                            45
Spectroscopy
Spectroscopy   2.ALKENES:

               The molecular ion of alkene containing one double bond tends to
               undergo allylic cleavage i.e. at the beta bond without the double
               bond and gives resonance structure.
               · The molecular ion peak in the spectra of unsaturated compounds
               is more intense than the corresponding saturated analogues. The
               reason is the better resonance stabilization of the charge on the
               cation formed by the removal of one of the π-electrons.
               · The relative abundance of the molecular ion peak decreases with
               increase in molecular mass.
               · The cyclic olefine also shows group of peaks which are 14 mass
               units apart.
               ·The general mode of fragmentation is the allylic cleavage.
               ·The fragments formed by Mc Lafferty rearrangement are more
               intense.

               Ex: 1-pentene.                                           46
Spectroscopy
Spectroscopy
               Cycloalkenes usually show a distinct molecular ion peak. A unique
               mode of cleavage is a type of Retro Diels-Alder reaction. The
               fragmentation mode involves the cleavage of two bonds of a cyclic
               system resulting in the formation of two stable unsaturated fragments
               in which two new bonds are formed.




               Aromatic compounds: 
                It shows prominent mol ion peak, as compared to the alkanes and
                 alkenes containing same number of C atoms. This is as a result of the
                 stabilizing effect of the ring.
                In these compounds M++1 and M++2 are also noticed, due to C13.
                  If aromatic ring is substituted by an alkyl groups a prominent peak is
                  formed at m/z91. Here benzyl (C6H5C+H2) cation formed rearranges
                  to tropylium cation (C7H7+). This may eliminate a neutral acetylene
                  molecule to give a peak at m/e 65.                               47
Spectroscopy
Spectroscopy
               Ex: Ethyl benzene

               Alcohols:
                    The molecular ion peak of 1º and 2ºalcohol is usually of
                 low abundance. It is not detected in 3º alcohols.
                The fragmentation modes in alcohols depend upon the
                 fact whether it is 1º, 2º or 3º alcohols.
                The fragmentation of C-C bond adjacent to oxygen atom
                 is the preferred fragmentation mode i.e. α cleavage.
                1º alcohols shows M-18 peaks, corresponding to the loss
                 of water.
                    Long chain members may show peaks corresponding to
                 successive loss of H radicals at M-1, M-2 and M-3.
                    The CH2=OH is the most significant peak in the spectra
                 of 1º alcohols.
                    Secondary alcohols cleave to give prominent peaks due
                 R-CH=OH at m/z=45,59,73.                                   48
Spectroscopy
Spectroscopy   Aromatic alcohols:

               The relative abundance of the parent ion of aromatic alcohols is
               large.
               Some of the fragment modes of benzyl alcohol are loss of one,
               two or three hydrogen atoms
               M+H fragment of Benzyl alcohol also rearranges to form
               hydroxy tropylium ion.
               The OH group in the Benzyl positions fragments in a way,
               which favors charge retention on the aryl group.
               Phenols:
                The molecular ion peak is intense.
                The peak due to the loss of hydrogen radical, M+ - H is small.
                The fragment ion due to the loss of carbon monoxide is
                  significant.
                 Cresols form very intense peak due to the formation of
                  hydroxyl tropylium ion.                                 49
Spectroscopy
Spectroscopy   Aldehydes
                 The Molecular ion peak of aliphatic Aldehydes is weak.
                 Aromatic Aldehydes shows moderate intense peak.
                 R-CH=O+                    R-C≡O+ + H+
                 Characteristic feature of Aldehyde (especially Aromatic
                 Aldehyde) is loss of α hydrogen.
                 Second common feature of Aliphatic Aldehyde is β cleavage.
                 For ex, Aldehyde with CH2-CHO end group gives rise to
                characteristic M-43 peaks.

               Ketones:
                Molecular ion peaks are intense than Aldehyde.Most of the
                 abundant ions in the mass spectra of Ketones can be accounted
                 by α cleavage and Mc Lafferty rearrangement.



                                                                        50
Spectroscopy
Spectroscopy   Nitro Compounds:
                  Aliphatic Nitro compounds fragment by loss of NO2 to give
                  strong carbonium ion.
                  R-NO2+              R+ + NO2
                  An Mc Lafferty rearrangement occurs but such type of peaks
                  are weak.
                  Nitrites show β cleavage .
               Aliphatic acids:
                The molecular ion peak in aliphatic acids is less intense as
                  compared to that of aromatic acids.Carboxyl group is directly
                  eliminated by α cleavage and a signal is formed at m/e 45.
                If α carbon atom is not substituted in aliphatic acids
                  containing a gamma hydrogen atom, Mc Lafferty
                  rearrangement ion is formed at m/e 60. It is often the base
                  peak.
                In short chain acids, M-OH and M-COOH peaks are
                  prominent.
                                                                          51
Halogen Compounds:
Spectroscopy
Spectroscopy

                      A compound with 1 chlorine atom gives a M+2 peak,
                   which is one third the intensity of the molecular ion peak
                   due to the presence of Molecular ion containing 37Cl isotope.
                      In a mono bromo derivative the M+2 peak is almost of
                   equal intensity to the molecular ion and is due to the
                   presence of molecular ion containing 81Br isotope.
                       Fluorine and Iodine being mono isotopic do not give
                   these patterns.
                       Aliphatic chlorine compounds fragment mainly by the
                   loss of HCl to give peaks at M-36 and M-38. HCl peaks can
                   also be seen at m/z 36, 38.
                       The relative abundance of the Molecular ion decreases
                   with increase in chain length and increase in branching.

                                                                           52
Ethers:
Spectroscopy
Spectroscopy
                Aliphatic ethers undergo facile fragmentation and exhibit
                 a weak molecular ion peak because the resultant ion is
                 highly stabilized by resonance.
                The major fragmentation modes occur through α and β
                 cleavages
                    α cleavage : Cleavage of a bond α to oxygen occurs, the
                 positive charge being retained on the carbon rather than on
                 oxygen.
                    β cleavage: A heteroatom induces cleavage at a bond β
                 to it. Such a cleavage favors the loss of larger group as a
                 radical. The ion undergoes further fragmentation to give the
                 series of ions.
                  Ex: Diethyl ether.

               Aromatic Ethers:
                   The Molecular ion peak of aromatic ether is prominent.
                  Primary cleavage occurs at the bond β to the ring and first
                 formed ions can decompose further.                        53
Spectroscopy
Spectroscopy
               IMPORTANT QUESTIONS:
               1. State the basic principles of mass spectroscopy. Write about
                  different types of ions produces in a mass spectrometer. What
                  are the general rules for fragmentation pattern in molecules.
                  (2010).20 marks.
               2. What are the general rules predicting prominent peaks in a
                  mass spectrum.(Oct’2009).10 marks.
               3. Outline principle of mass spectrometry.(2003,2004)10 marks
               4. Explain rules of fragmentation in mass spectroscopy with one
                  example each.(2006).10marks.
               5. With an example concept of ring rule.(2006).5marks.
Spectroscopy
Spectroscopy   References:
               1. Sharma Y.R. Elementary organic spectroscopy principles and
                  chemical applications. 1st ed. S. Chand and Company ltd; New
                  Delhi :2008.

               5. Chatwal G.R, Anand S.K. Instrumental methods of chemical
                  analysis. 1st ed. Himalaya Publishing house; Mumbai: 2004.

               5. S. Ravi Shankar. Text book of pharmaceutical analysis. 3rd ed.
                  Rx publication; Tirunelveli: 2006.

               6. Skoog DA, West DM. principle of instrumental analysis. 2 ed
                  edition

                                                                   55
THANK UUUUUUUUUUUU
Spectroscopy
Spectroscopy

Weitere ähnliche Inhalte

Was ist angesagt?

Mass spectroscopy, Ionization techniques and types of mass analyzers
Mass spectroscopy, Ionization techniques and types of mass analyzers Mass spectroscopy, Ionization techniques and types of mass analyzers
Mass spectroscopy, Ionization techniques and types of mass analyzers Muhammad Asif Shaheeen
 
NMR spectroscopy
NMR spectroscopyNMR spectroscopy
NMR spectroscopyAFSATH
 
Infrared spectroscopy
Infrared spectroscopyInfrared spectroscopy
Infrared spectroscopyNida Ashraf
 
Ion exchange chromatography
Ion exchange chromatography Ion exchange chromatography
Ion exchange chromatography Vharsha Haran
 
Column Chromatography ppt
Column Chromatography pptColumn Chromatography ppt
Column Chromatography pptshaisejacob
 
Infrared spectroscopy
Infrared spectroscopyInfrared spectroscopy
Infrared spectroscopyAsma Ashraf
 
Ion exchange Chromatography
Ion exchange ChromatographyIon exchange Chromatography
Ion exchange ChromatographyKuldeep Sharma
 
MASS SPECTROSCOPY & ITS INSTRUMENTATION
MASS SPECTROSCOPY & ITS INSTRUMENTATIONMASS SPECTROSCOPY & ITS INSTRUMENTATION
MASS SPECTROSCOPY & ITS INSTRUMENTATIONROHIT
 
UV-Visible spectroscopy
UV-Visible spectroscopyUV-Visible spectroscopy
UV-Visible spectroscopyMehulJain143
 
Factors influencing chemical shift
Factors influencing chemical shiftFactors influencing chemical shift
Factors influencing chemical shiftKavitha Bitra
 
HPLC AND ITS APPLICATIONS
HPLC AND ITS APPLICATIONS HPLC AND ITS APPLICATIONS
HPLC AND ITS APPLICATIONS drakhtar06
 
Atomic absorption spectroscopy
Atomic absorption spectroscopy Atomic absorption spectroscopy
Atomic absorption spectroscopy Mayur Bodhankar
 

Was ist angesagt? (20)

Mass spectroscopy, Ionization techniques and types of mass analyzers
Mass spectroscopy, Ionization techniques and types of mass analyzers Mass spectroscopy, Ionization techniques and types of mass analyzers
Mass spectroscopy, Ionization techniques and types of mass analyzers
 
NMR spectroscopy
NMR spectroscopyNMR spectroscopy
NMR spectroscopy
 
FLAME EMISSION SPECTROSCOPY
FLAME EMISSION SPECTROSCOPY FLAME EMISSION SPECTROSCOPY
FLAME EMISSION SPECTROSCOPY
 
Infrared spectroscopy
Infrared spectroscopyInfrared spectroscopy
Infrared spectroscopy
 
Mass Analyser
Mass AnalyserMass Analyser
Mass Analyser
 
Ion exchange chromatography
Ion exchange chromatography Ion exchange chromatography
Ion exchange chromatography
 
Column Chromatography ppt
Column Chromatography pptColumn Chromatography ppt
Column Chromatography ppt
 
Ion exchange chromatography
Ion  exchange chromatographyIon  exchange chromatography
Ion exchange chromatography
 
Infrared spectroscopy
Infrared spectroscopyInfrared spectroscopy
Infrared spectroscopy
 
Ion exchange Chromatography
Ion exchange ChromatographyIon exchange Chromatography
Ion exchange Chromatography
 
Lc ms
Lc msLc ms
Lc ms
 
MASS SPECTROSCOPY & ITS INSTRUMENTATION
MASS SPECTROSCOPY & ITS INSTRUMENTATIONMASS SPECTROSCOPY & ITS INSTRUMENTATION
MASS SPECTROSCOPY & ITS INSTRUMENTATION
 
Capillary electrophoresis
Capillary electrophoresisCapillary electrophoresis
Capillary electrophoresis
 
UV-Visible spectroscopy
UV-Visible spectroscopyUV-Visible spectroscopy
UV-Visible spectroscopy
 
Mass spectrometry
Mass spectrometryMass spectrometry
Mass spectrometry
 
Factors influencing chemical shift
Factors influencing chemical shiftFactors influencing chemical shift
Factors influencing chemical shift
 
HPLC AND ITS APPLICATIONS
HPLC AND ITS APPLICATIONS HPLC AND ITS APPLICATIONS
HPLC AND ITS APPLICATIONS
 
IR Spectroscopy
IR Spectroscopy IR Spectroscopy
IR Spectroscopy
 
HPLC
HPLCHPLC
HPLC
 
Atomic absorption spectroscopy
Atomic absorption spectroscopy Atomic absorption spectroscopy
Atomic absorption spectroscopy
 

Andere mochten auch

Andere mochten auch (20)

Mass spectrometry
Mass spectrometryMass spectrometry
Mass spectrometry
 
Mass spectroscopy pdf
Mass spectroscopy  pdfMass spectroscopy  pdf
Mass spectroscopy pdf
 
Mass spectrometry
Mass spectrometryMass spectrometry
Mass spectrometry
 
Mass spectrometry hh
Mass spectrometry hhMass spectrometry hh
Mass spectrometry hh
 
Mass spectrometry
Mass spectrometryMass spectrometry
Mass spectrometry
 
Mass spectrometry
Mass spectrometryMass spectrometry
Mass spectrometry
 
MASS SPECTROMETRY(mass-spec) -2013 - P.ravisankar- WHAT ABOUT MASS SPECTROMET...
MASS SPECTROMETRY(mass-spec) -2013 - P.ravisankar- WHAT ABOUT MASS SPECTROMET...MASS SPECTROMETRY(mass-spec) -2013 - P.ravisankar- WHAT ABOUT MASS SPECTROMET...
MASS SPECTROMETRY(mass-spec) -2013 - P.ravisankar- WHAT ABOUT MASS SPECTROMET...
 
ISOELECTRIC FOCUSING PPT - SLIDE SHARE
ISOELECTRIC FOCUSING PPT - SLIDE SHAREISOELECTRIC FOCUSING PPT - SLIDE SHARE
ISOELECTRIC FOCUSING PPT - SLIDE SHARE
 
Mass spectrometry
Mass spectrometry Mass spectrometry
Mass spectrometry
 
Spectrofluorimetry
SpectrofluorimetrySpectrofluorimetry
Spectrofluorimetry
 
Nmr spectroscopy
Nmr spectroscopyNmr spectroscopy
Nmr spectroscopy
 
Isoelectric Focusing
Isoelectric FocusingIsoelectric Focusing
Isoelectric Focusing
 
Nmr spectroscopy
Nmr spectroscopyNmr spectroscopy
Nmr spectroscopy
 
Spectrofluorimetry Lecture
Spectrofluorimetry LectureSpectrofluorimetry Lecture
Spectrofluorimetry Lecture
 
Quantum numbers
Quantum numbersQuantum numbers
Quantum numbers
 
Spectrofluorimetry
SpectrofluorimetrySpectrofluorimetry
Spectrofluorimetry
 
Mass spectroscopy
Mass spectroscopyMass spectroscopy
Mass spectroscopy
 
Introduction, Principle, Instrumentation and Applications of SDS-PAGE
Introduction, Principle, Instrumentation and Applications of SDS-PAGEIntroduction, Principle, Instrumentation and Applications of SDS-PAGE
Introduction, Principle, Instrumentation and Applications of SDS-PAGE
 
TDDS
TDDSTDDS
TDDS
 
Ppt on transdermal
Ppt on transdermalPpt on transdermal
Ppt on transdermal
 

Ähnlich wie Mass Spectroscopy: A Guide to Principles and Applications

2 amrutamass-130210233002-phpapp02
2 amrutamass-130210233002-phpapp022 amrutamass-130210233002-phpapp02
2 amrutamass-130210233002-phpapp02illyas_77
 
MASS SPECTROSCOPY.pptx
MASS SPECTROSCOPY.pptxMASS SPECTROSCOPY.pptx
MASS SPECTROSCOPY.pptxMO.SHAHANAWAZ
 
Identification and detection of molecules
Identification and detection of moleculesIdentification and detection of molecules
Identification and detection of moleculesKaavya Sudhakar
 
Mass spectrometry- full lecture
Mass spectrometry- full lecture Mass spectrometry- full lecture
Mass spectrometry- full lecture DRZIAMUHAMMAD2
 
atomic absorption spectroscopy and mass spectroscopy
atomic absorption spectroscopy and mass spectroscopyatomic absorption spectroscopy and mass spectroscopy
atomic absorption spectroscopy and mass spectroscopyvanitha gopal
 
Mass Spectrometry ppt.pptx
Mass Spectrometry ppt.pptxMass Spectrometry ppt.pptx
Mass Spectrometry ppt.pptxJaibhagwan47
 
Presentation on MASS SPECTROSCOPY.pptx
Presentation on MASS SPECTROSCOPY.pptxPresentation on MASS SPECTROSCOPY.pptx
Presentation on MASS SPECTROSCOPY.pptxTapasMajumder15
 
Classification of Spectroscopy by Dr. Ved Nath Jha.pptx
Classification of Spectroscopy by Dr. Ved Nath Jha.pptxClassification of Spectroscopy by Dr. Ved Nath Jha.pptx
Classification of Spectroscopy by Dr. Ved Nath Jha.pptxDrVednathJha1
 
Spectroscopy for Pharmaceutical Analysis and Instrumental Method of Analysis....
Spectroscopy for Pharmaceutical Analysis and Instrumental Method of Analysis....Spectroscopy for Pharmaceutical Analysis and Instrumental Method of Analysis....
Spectroscopy for Pharmaceutical Analysis and Instrumental Method of Analysis....Yunesalsayadi
 

Ähnlich wie Mass Spectroscopy: A Guide to Principles and Applications (20)

4. mass jntu pharmacy
4. mass jntu pharmacy4. mass jntu pharmacy
4. mass jntu pharmacy
 
2 amrutamass-130210233002-phpapp02
2 amrutamass-130210233002-phpapp022 amrutamass-130210233002-phpapp02
2 amrutamass-130210233002-phpapp02
 
Mass spectroscopy(1)
Mass spectroscopy(1)Mass spectroscopy(1)
Mass spectroscopy(1)
 
Mass Spectroscopy
Mass SpectroscopyMass Spectroscopy
Mass Spectroscopy
 
Mass Spectrometry
Mass SpectrometryMass Spectrometry
Mass Spectrometry
 
MASS SPECTROSCOPY.pptx
MASS SPECTROSCOPY.pptxMASS SPECTROSCOPY.pptx
MASS SPECTROSCOPY.pptx
 
Identification and detection of molecules
Identification and detection of moleculesIdentification and detection of molecules
Identification and detection of molecules
 
Mass analyse rs by bashant
Mass analyse rs by bashantMass analyse rs by bashant
Mass analyse rs by bashant
 
mass shruti
mass shrutimass shruti
mass shruti
 
Mass spectrometry- full lecture
Mass spectrometry- full lecture Mass spectrometry- full lecture
Mass spectrometry- full lecture
 
Applied Biochemistry
Applied BiochemistryApplied Biochemistry
Applied Biochemistry
 
atomic absorption spectroscopy and mass spectroscopy
atomic absorption spectroscopy and mass spectroscopyatomic absorption spectroscopy and mass spectroscopy
atomic absorption spectroscopy and mass spectroscopy
 
Spectroscopy
Spectroscopy Spectroscopy
Spectroscopy
 
Mass spectrometry
Mass spectrometryMass spectrometry
Mass spectrometry
 
Mass Spectrometry ppt.pptx
Mass Spectrometry ppt.pptxMass Spectrometry ppt.pptx
Mass Spectrometry ppt.pptx
 
Presentation on MASS SPECTROSCOPY.pptx
Presentation on MASS SPECTROSCOPY.pptxPresentation on MASS SPECTROSCOPY.pptx
Presentation on MASS SPECTROSCOPY.pptx
 
Mass spectrometry - A detailed study on components
Mass spectrometry - A detailed study on components Mass spectrometry - A detailed study on components
Mass spectrometry - A detailed study on components
 
Introduction to Spectroscopy
Introduction to SpectroscopyIntroduction to Spectroscopy
Introduction to Spectroscopy
 
Classification of Spectroscopy by Dr. Ved Nath Jha.pptx
Classification of Spectroscopy by Dr. Ved Nath Jha.pptxClassification of Spectroscopy by Dr. Ved Nath Jha.pptx
Classification of Spectroscopy by Dr. Ved Nath Jha.pptx
 
Spectroscopy for Pharmaceutical Analysis and Instrumental Method of Analysis....
Spectroscopy for Pharmaceutical Analysis and Instrumental Method of Analysis....Spectroscopy for Pharmaceutical Analysis and Instrumental Method of Analysis....
Spectroscopy for Pharmaceutical Analysis and Instrumental Method of Analysis....
 

Mehr von AmrutaSambrekar

Thin Layer Chroatography
Thin Layer ChroatographyThin Layer Chroatography
Thin Layer ChroatographyAmrutaSambrekar
 
Nasal & Pulmonary Drug Delivery System
Nasal & Pulmonary Drug Delivery SystemNasal & Pulmonary Drug Delivery System
Nasal & Pulmonary Drug Delivery SystemAmrutaSambrekar
 
Rate Controlled Drug Delivery System
Rate Controlled Drug Delivery SystemRate Controlled Drug Delivery System
Rate Controlled Drug Delivery SystemAmrutaSambrekar
 

Mehr von AmrutaSambrekar (6)

Dosage Regimen
Dosage RegimenDosage Regimen
Dosage Regimen
 
Bioavailability Studies
Bioavailability StudiesBioavailability Studies
Bioavailability Studies
 
Thin Layer Chroatography
Thin Layer ChroatographyThin Layer Chroatography
Thin Layer Chroatography
 
Nasal & Pulmonary Drug Delivery System
Nasal & Pulmonary Drug Delivery SystemNasal & Pulmonary Drug Delivery System
Nasal & Pulmonary Drug Delivery System
 
Rate Controlled Drug Delivery System
Rate Controlled Drug Delivery SystemRate Controlled Drug Delivery System
Rate Controlled Drug Delivery System
 
Material Management
Material Management Material Management
Material Management
 

Kürzlich hochgeladen

How to Share Dashboard in the Odoo 17 ERP
How to Share Dashboard in the Odoo 17 ERPHow to Share Dashboard in the Odoo 17 ERP
How to Share Dashboard in the Odoo 17 ERPCeline George
 
16. Discovery, function and commercial uses of different PGRS.pptx
16. Discovery, function and commercial uses of different PGRS.pptx16. Discovery, function and commercial uses of different PGRS.pptx
16. Discovery, function and commercial uses of different PGRS.pptxUmeshTimilsina1
 
Paul Dobryden In Media Res Media Component
Paul Dobryden In Media Res Media ComponentPaul Dobryden In Media Res Media Component
Paul Dobryden In Media Res Media ComponentInMediaRes1
 
4.4.24 Economic Precarity and Global Economic Forces.pptx
4.4.24 Economic Precarity and Global Economic Forces.pptx4.4.24 Economic Precarity and Global Economic Forces.pptx
4.4.24 Economic Precarity and Global Economic Forces.pptxmary850239
 
LEVERAGING SYNERGISM INDUSTRY-ACADEMIA PARTNERSHIP FOR IMPLEMENTATION OF NAT...
LEVERAGING SYNERGISM INDUSTRY-ACADEMIA PARTNERSHIP FOR IMPLEMENTATION OF  NAT...LEVERAGING SYNERGISM INDUSTRY-ACADEMIA PARTNERSHIP FOR IMPLEMENTATION OF  NAT...
LEVERAGING SYNERGISM INDUSTRY-ACADEMIA PARTNERSHIP FOR IMPLEMENTATION OF NAT...pragatimahajan3
 
18. Training and prunning of horicultural crops.pptx
18. Training and prunning of horicultural crops.pptx18. Training and prunning of horicultural crops.pptx
18. Training and prunning of horicultural crops.pptxUmeshTimilsina1
 
Healthy Minds, Flourishing Lives: A Philosophical Approach to Mental Health a...
Healthy Minds, Flourishing Lives: A Philosophical Approach to Mental Health a...Healthy Minds, Flourishing Lives: A Philosophical Approach to Mental Health a...
Healthy Minds, Flourishing Lives: A Philosophical Approach to Mental Health a...Osopher
 
HackerOne X IoT Lab Bug Bounty 101 with Encryptsaan & IoT Lab at KIIT Univers...
HackerOne X IoT Lab Bug Bounty 101 with Encryptsaan & IoT Lab at KIIT Univers...HackerOne X IoT Lab Bug Bounty 101 with Encryptsaan & IoT Lab at KIIT Univers...
HackerOne X IoT Lab Bug Bounty 101 with Encryptsaan & IoT Lab at KIIT Univers...kumarpriyanshu81
 
(Part 2) CHILDREN'S DISABILITIES AND EXCEPTIONALITIES.pdf
(Part 2) CHILDREN'S DISABILITIES AND EXCEPTIONALITIES.pdf(Part 2) CHILDREN'S DISABILITIES AND EXCEPTIONALITIES.pdf
(Part 2) CHILDREN'S DISABILITIES AND EXCEPTIONALITIES.pdfMJDuyan
 
BÀI TẬP BỔ TRỢ TIẾNG ANH 8 - I-LEARN SMART WORLD - CẢ NĂM - CÓ FILE NGHE (BẢN...
BÀI TẬP BỔ TRỢ TIẾNG ANH 8 - I-LEARN SMART WORLD - CẢ NĂM - CÓ FILE NGHE (BẢN...BÀI TẬP BỔ TRỢ TIẾNG ANH 8 - I-LEARN SMART WORLD - CẢ NĂM - CÓ FILE NGHE (BẢN...
BÀI TẬP BỔ TRỢ TIẾNG ANH 8 - I-LEARN SMART WORLD - CẢ NĂM - CÓ FILE NGHE (BẢN...Nguyen Thanh Tu Collection
 
What is Property Fields in Odoo 17 ERP Module
What is Property Fields in Odoo 17 ERP ModuleWhat is Property Fields in Odoo 17 ERP Module
What is Property Fields in Odoo 17 ERP ModuleCeline George
 
The Shop Floor Overview in the Odoo 17 ERP
The Shop Floor Overview in the Odoo 17 ERPThe Shop Floor Overview in the Odoo 17 ERP
The Shop Floor Overview in the Odoo 17 ERPCeline George
 
Executive Directors Chat Initiating Equity for Impact.pdf
Executive Directors Chat  Initiating Equity for Impact.pdfExecutive Directors Chat  Initiating Equity for Impact.pdf
Executive Directors Chat Initiating Equity for Impact.pdfTechSoup
 
Farrington HS Streamlines Guest Entrance
Farrington HS Streamlines Guest EntranceFarrington HS Streamlines Guest Entrance
Farrington HS Streamlines Guest Entrancejulius27264
 
Views in Odoo 17 - Kanban View in odoo 17
Views in Odoo 17 - Kanban View  in odoo 17Views in Odoo 17 - Kanban View  in odoo 17
Views in Odoo 17 - Kanban View in odoo 17Celine George
 
Transdisciplinary Pathways for Urban Resilience [Work in Progress].pptx
Transdisciplinary Pathways for Urban Resilience [Work in Progress].pptxTransdisciplinary Pathways for Urban Resilience [Work in Progress].pptx
Transdisciplinary Pathways for Urban Resilience [Work in Progress].pptxinfo924062
 
Sulphonamides, mechanisms and their uses
Sulphonamides, mechanisms and their usesSulphonamides, mechanisms and their uses
Sulphonamides, mechanisms and their usesVijayaLaxmi84
 
6 ways Samsung’s Interactive Display powered by Android changes the classroom
6 ways Samsung’s Interactive Display powered by Android changes the classroom6 ways Samsung’s Interactive Display powered by Android changes the classroom
6 ways Samsung’s Interactive Display powered by Android changes the classroomSamsung Business USA
 

Kürzlich hochgeladen (20)

How to Share Dashboard in the Odoo 17 ERP
How to Share Dashboard in the Odoo 17 ERPHow to Share Dashboard in the Odoo 17 ERP
How to Share Dashboard in the Odoo 17 ERP
 
Israel Genealogy Research Assoc. April 2024 Database Release
Israel Genealogy Research Assoc. April 2024 Database ReleaseIsrael Genealogy Research Assoc. April 2024 Database Release
Israel Genealogy Research Assoc. April 2024 Database Release
 
16. Discovery, function and commercial uses of different PGRS.pptx
16. Discovery, function and commercial uses of different PGRS.pptx16. Discovery, function and commercial uses of different PGRS.pptx
16. Discovery, function and commercial uses of different PGRS.pptx
 
Paul Dobryden In Media Res Media Component
Paul Dobryden In Media Res Media ComponentPaul Dobryden In Media Res Media Component
Paul Dobryden In Media Res Media Component
 
4.4.24 Economic Precarity and Global Economic Forces.pptx
4.4.24 Economic Precarity and Global Economic Forces.pptx4.4.24 Economic Precarity and Global Economic Forces.pptx
4.4.24 Economic Precarity and Global Economic Forces.pptx
 
LEVERAGING SYNERGISM INDUSTRY-ACADEMIA PARTNERSHIP FOR IMPLEMENTATION OF NAT...
LEVERAGING SYNERGISM INDUSTRY-ACADEMIA PARTNERSHIP FOR IMPLEMENTATION OF  NAT...LEVERAGING SYNERGISM INDUSTRY-ACADEMIA PARTNERSHIP FOR IMPLEMENTATION OF  NAT...
LEVERAGING SYNERGISM INDUSTRY-ACADEMIA PARTNERSHIP FOR IMPLEMENTATION OF NAT...
 
18. Training and prunning of horicultural crops.pptx
18. Training and prunning of horicultural crops.pptx18. Training and prunning of horicultural crops.pptx
18. Training and prunning of horicultural crops.pptx
 
Healthy Minds, Flourishing Lives: A Philosophical Approach to Mental Health a...
Healthy Minds, Flourishing Lives: A Philosophical Approach to Mental Health a...Healthy Minds, Flourishing Lives: A Philosophical Approach to Mental Health a...
Healthy Minds, Flourishing Lives: A Philosophical Approach to Mental Health a...
 
HackerOne X IoT Lab Bug Bounty 101 with Encryptsaan & IoT Lab at KIIT Univers...
HackerOne X IoT Lab Bug Bounty 101 with Encryptsaan & IoT Lab at KIIT Univers...HackerOne X IoT Lab Bug Bounty 101 with Encryptsaan & IoT Lab at KIIT Univers...
HackerOne X IoT Lab Bug Bounty 101 with Encryptsaan & IoT Lab at KIIT Univers...
 
(Part 2) CHILDREN'S DISABILITIES AND EXCEPTIONALITIES.pdf
(Part 2) CHILDREN'S DISABILITIES AND EXCEPTIONALITIES.pdf(Part 2) CHILDREN'S DISABILITIES AND EXCEPTIONALITIES.pdf
(Part 2) CHILDREN'S DISABILITIES AND EXCEPTIONALITIES.pdf
 
BÀI TẬP BỔ TRỢ TIẾNG ANH 8 - I-LEARN SMART WORLD - CẢ NĂM - CÓ FILE NGHE (BẢN...
BÀI TẬP BỔ TRỢ TIẾNG ANH 8 - I-LEARN SMART WORLD - CẢ NĂM - CÓ FILE NGHE (BẢN...BÀI TẬP BỔ TRỢ TIẾNG ANH 8 - I-LEARN SMART WORLD - CẢ NĂM - CÓ FILE NGHE (BẢN...
BÀI TẬP BỔ TRỢ TIẾNG ANH 8 - I-LEARN SMART WORLD - CẢ NĂM - CÓ FILE NGHE (BẢN...
 
What is Property Fields in Odoo 17 ERP Module
What is Property Fields in Odoo 17 ERP ModuleWhat is Property Fields in Odoo 17 ERP Module
What is Property Fields in Odoo 17 ERP Module
 
The Shop Floor Overview in the Odoo 17 ERP
The Shop Floor Overview in the Odoo 17 ERPThe Shop Floor Overview in the Odoo 17 ERP
The Shop Floor Overview in the Odoo 17 ERP
 
Executive Directors Chat Initiating Equity for Impact.pdf
Executive Directors Chat  Initiating Equity for Impact.pdfExecutive Directors Chat  Initiating Equity for Impact.pdf
Executive Directors Chat Initiating Equity for Impact.pdf
 
Farrington HS Streamlines Guest Entrance
Farrington HS Streamlines Guest EntranceFarrington HS Streamlines Guest Entrance
Farrington HS Streamlines Guest Entrance
 
Views in Odoo 17 - Kanban View in odoo 17
Views in Odoo 17 - Kanban View  in odoo 17Views in Odoo 17 - Kanban View  in odoo 17
Views in Odoo 17 - Kanban View in odoo 17
 
Transdisciplinary Pathways for Urban Resilience [Work in Progress].pptx
Transdisciplinary Pathways for Urban Resilience [Work in Progress].pptxTransdisciplinary Pathways for Urban Resilience [Work in Progress].pptx
Transdisciplinary Pathways for Urban Resilience [Work in Progress].pptx
 
CARNAVAL COM MAGIA E EUFORIA _
CARNAVAL COM MAGIA E EUFORIA            _CARNAVAL COM MAGIA E EUFORIA            _
CARNAVAL COM MAGIA E EUFORIA _
 
Sulphonamides, mechanisms and their uses
Sulphonamides, mechanisms and their usesSulphonamides, mechanisms and their uses
Sulphonamides, mechanisms and their uses
 
6 ways Samsung’s Interactive Display powered by Android changes the classroom
6 ways Samsung’s Interactive Display powered by Android changes the classroom6 ways Samsung’s Interactive Display powered by Android changes the classroom
6 ways Samsung’s Interactive Display powered by Android changes the classroom
 

Mass Spectroscopy: A Guide to Principles and Applications

  • 1. Spectroscopy Spectroscopy MASS SPECTROSCOPY -: Presented By :- Amruta S. Sambarekar 1st Year M.Pharm Dept. of Pharmaceutics M M C P, BELGAUM. 1
  • 2. Spectroscopy Spectroscopy Contents  Introduction  Basic principle  Theory  Brief outline of instrumentation.  Ion formation and types  Fragmentation processes  Fragmentation patterns  Fragmentation characteristics in relation to parent structure and functional groups 2
  • 3. Spectroscopy Spectroscopy Mass spectroscopy Mass spectroscopy is one of the primary spectroscopic methods for molecular analysis available to organic chemist. It is a microanalytical technique requiring only a few nanomoles of the sample to obtain characteristic information pertaining to the structure and molecular weight of analyte. It is not concerned with non- destructive interaction between molecules and electromagnetic radiation. 3
  • 4. Spectroscopy Spectroscopy It involves the production and separation of ionised molecules and their ionic decompositon product and finally the measurement of the relative abundance of different ions produced. It is, thus a destructive technique in that the sample is consumed during analysis. In most cases, the nascent molecular ion of the analyte produced fragment ions by cleavage of the bond and the resulting fragmentation pattern constitutes the mass spectrum. Thus, the mass spectrum of each compound is unique and can be used as a “chemical fingerprint” to characterize the sample. 4
  • 5. Spectroscopy Basic principle Spectroscopy Mass spectroscopy is the most accurate method for determining the molecular mass of the compound and its elemental composition. In this technique, molecules are bombarded with a beam of energetic electrons. The molecules are ionised and broken up into many fragments, some of which are positive ions. Each kind of ion has a particular ratio of mass to charge, i.e. m/e ratio(value). For most ions, the charge is one and thus, m/e ratio is simply the molecular mass of the ion. 5
  • 6. Spectroscopy Spectroscopy Mass spectra is used in two general ways: 1) To prove the identity of two compounds. 2) To establish the structure of a new a compound. The mass spectrum of a compound helps to establish the structure of a new compound in several different ways: 1) It can give the exact molecular mass. 2) It can give a molecular formula or it can reveal the presence of certain structural units in a molecule. 6
  • 7. Spectroscopy Spectroscopy Basic theory  Mass spectroscopy deals with the examination of the characteristics fragments(ions) arising from the breakdown of organic molecules. A mass spectrum is the plot of relative abundance of ions against their mass/charge ratio. The basic aspect of organic mass spectrometry consist of bombarding the vapour of an organic compound with a beam of energetic electron accelarated from a filament to an energy of 70 eV to form positively charged ions (molecular ions). 7
  • 8. Spectroscopy Spectroscopy  The additional energy of the elecrons is dissipated in breaking the bonds in the molecular ion, which undergoes fragmentation to yield several neutral or positively charged species. This fragmentation may result in the formation of an even- electron ion and radical. The various positive ions, thus formed, can be accelerated and deflected by magnetic or electric fields. The deflection of ions, however, depends on its mass, charge and velocity. 8
  • 9. Spectroscopy Spectroscopy  For a given charge, velocity and deflecting force, the deflection is less for a heavy particle as compared to that of a light one. Thus, a number of beams each containing ions with the same m/z values are obtained. These beams are then made to strike against a photographic plate where not only they appear as separate lines but the intensity of each peak is also recorded. The clear visual presentation of a mass spectum is usually obtain by plotting m/z value against relative abundance, assigning the most abundant ion (base peak)in the spectrum as 100 per cent. 9
  • 10. Spectroscopy Spectroscopy  Though organic mass spectrometry is routinely used along with IR, NMR and UV for structure detemination, its basic theory is different from the others.  In mass spectrometry no characteristic selective absorption of radiation is involved as in the case of the other three methods, secondly, in the mass spectrometry, the compound undergoes irriversible chemical changes unlike in the others, where the changes are reversible physical changes. The mass spectral reactions are much more drastic than usual chemical reactions. 10
  • 11. Spectroscopy Spectroscopy Principle and Instrumentation 11
  • 12. Ionisation Spectroscopy Spectroscopy The atom is ionised by knocking one or more electrons off to give a positive ion. (Mass spectrometers always work with positive ions). The particles in the sample (atoms or molecules) are bombarded with a stream of electrons to knock one or more electrons out of the sample particles to make positive ions. 12
  • 13. Spectroscopy Spectroscopy Most of the positive ions formed will carry a charge of +1. These positive ions are persuaded out into the rest of the machine by the ion repeller which is another metal plate carrying a slight positive charge. 13
  • 14.  Acceleration Spectroscopy Spectroscopy  The ions are accelerated so that they all have the same kinetic energy. 14
  • 15. Spectroscopy Spectroscopy The positive ions are repelled away from the positive ionisation chamber and pass through three slits with voltage in the decreasing order. The middle slit carries some intermediate voltage and the final at ‘0’ volts. All the ions are accelerated into a finely focused beam. 15
  • 16. Spectroscopy Spectroscopy  Deflection The ions are then deflected by a magnetic field according to their masses. The lighter they are, the more they are deflected. The amount of deflection also depends on the number of positive charges on the ion -The more the ion is charged, the more it gets deflected. 16
  • 17. Spectroscopy Spectroscopy Different ions are deflected by the magnetic field by different amounts. The amount of deflection depends on: The mass of the ion: Lighter ions are deflected more than heavier ones. The charge on the ion: Ions with 2 (or more) positive charges are deflected more than ones with only 1 positive charge. 17
  • 18.  Detection Spectroscopy Spectroscopy The beam of ions passing through the machine is detected electrically. Only ion stream B makes it right through the machine to the ion detector. The other ions collide with the walls where they will pick up electrons and be neutralised. They get removed from the mass spectrometer by the vacuum pump. When an ion hits the metal box, its charge is neutralised by an electron jumping from the metal on to the ion. 18
  • 19. Spectroscopy Spectroscopy That leaves a space amongst the electrons in the metal, and the electrons in the wire shuffle along to fill it. A flow of electrons in the wire is detected as an electric current which can be amplified and recorded. The more ions arriving, the greater the current. 19
  • 20. Spectroscopy Spectroscopy Fragmentation process:   Bombardment of molecules by an electron beam with energy between 10-15ev usually results in the ionization of molecules by removal of one electron (Molecular ion formation). When the energy of electron beam is increased between 50-70ev, these molecular ions acquire a high excitation resulting in their break down into various fragments. This process is called “ Fragmentation process”. 20
  • 21. Spectroscopy Spectroscopy Types of Ions:   1. Molecular ion or Parent ion. 2. Fragment ions. 3. Rearrangement ions. 4. Multicharged ions. 5. Negative ions. 6. Metastable ions. 21
  • 22. Spectroscopy Spectroscopy 1. Molecular ion or Parent ion: When a molecule is bombarded with electrons in high vacuum in Mass spectrometer, it is converted into positive ions by loss of an electron. These ions are called as Molecular or Parent ions. M + e → M+° + 2e— Where, M – represents the Molecule; M+°– represents the Molecular or Parent ion The order of energy required to remove electron is as follows— σ electrons > non-conjugated π > conjugated π > non bonding or lone pair of electrons. 22
  • 23. Spectroscopy Spectroscopy  Many of these molecular ions (M+°) disintegrate at 10-10 to 10-13 seconds to give a positively charged fragment and a radical in the simplest case. If some Molecular ions remain intact long enough (about 10-6 seconds) to reach the detector.  Most molecules show a peak for the molecular ion, the stability of which is usually in the order— Aromatic > Conjugated acyclic polyenes > Alicyclics > n- hydrocarbons > ketones > ethers> Branched chain hydrocarbons > Alcohols. 23
  • 24. Spectroscopy Spectroscopy Characteristics of Molecular ion: Molecular peak is observed if molecular ion remains intact long enough (10-6 seconds) to reach the detector. This peak gives the molecular weight of the compound. The molecular ion peak is usually the peak of the “highest mass number.” The molecular ion M+° has mass, corresponding to the molecular weight of the compound from which it is generated. Thus the mass of a Molecular ion M+° is an important parameter in the identification of the compound. 24
  • 25. Spectroscopy Spectroscopy Significance of Molecular ion: Molecular ion peak gives the molecular weight of the compound. i.e. m/z of molecular ion = molecular weight of the compound. Ex: C2H5+ (m/e=29) gives the molecular weight of Ethane. 2. Fragment ions: When the energy is given to Molecular ion during electron impact, further cleavage takes place and ions of lower mass number known as Fragment ions are produced. M+° → M+1 + M2 +° + Ex: CH3OH → CH2OH 3.Rearrangement ions: m/z 32 m/z 31 Rearrangement ions are the fragments whose origin cannot be described by simple cleavage of bonds in the parent ion, but are result of intramolecular atomic rearrangement during fragmentation. 25
  • 26. These are probably due to recombination of fragment ions and Spectroscopy Spectroscopy known as rearrangement peaks. Ex: Prominent peak in spectrum of diethyl ether occurs at m/e 31. This is due to the ions CH3O+, which is formed by rearrangement of C2H5O+ ions. 4. Multi charged ions: Some times ions may also exist with two or three charges instead of usual single charge in the mass spectrum. These are known as doubly or triply charged ions. They are created as follows: M+° + e- → M++ + 3e- But under normal operating conditions, most of the ions produced are single charged. The doubly or triply charged ions are recorded at a half or one third of the m/e value of the single charged ions. Formation of these multiple charged ions is more common in hetero aromatic compounds. They are also common in inorganic mass spectrum. Gases such as CO, N2,CO2 and O2 have measurable peaks corresponding to CO+2,N+2,and O+2. 26
  • 27. Spectroscopy Spectroscopy 5. Negative ions: The positive ions predominate in electronic impact ionization because of greater stability. The Negative ions are not very useful in structural determinations. The formation of Negative ions is very rare but these can be produced in three ways: 1.AB + e → A+ + B— 2.AB + e → AB— 3. AB + e → A+ + B— + e— 6. Metastable Ions: Fragment of a parent ion will give rise to a new ion (daughter) plus either a neutral molecule or a radical. M1+ M2+ + non charged particle An intermediate situation is possible; M1+ may decompose to M2+ while being accelerated. The resultant daughter ion M2+ will not be recorded at either M1 or M2, but at a position M* as a rather broad, poorly focused peak. Such an ion is called a metastable ion. 27
  • 29. Nature Of Metastable Ions: Spectroscopy Spectroscopy Metastable ions have lower kinetic energy than normal ions and metastable peaks are smaller than the M1 and M2 peaks and also broader. These metastable ions arise from fragmentation that takes place during the flight down through ion rather than in the ionization chamber. Molecular ions formed in the ionization chamber do one of the following things: 1. Either they decompose completely and very rapidly in the ion source and never reach the collector (as in case of highly branched molecular ions with life times less than 10-5 seconds). 2. Or else they survive long enough to reach the collector and be recorded there (life times longer than 10-5). 29
  • 30. Spectroscopy Spectroscopy Significance of Metastable ions: Metastable ions are useful in helping to establish fragments routes. Metastable ion peak can also be used to distinguish between fragmentation Processes, which occur in few microseconds. 30
  • 31. Spectroscopy Spectroscopy General rules for fragmentation: 1. The relative height of the molecular ion peak is greatest for the straight chain compound and decreases as the degree of branching increases. 2. The relative height of the Molecular ion peak usually decreases with increasing molecular weight in a homologous series. 3. Cleavage is favoured at alkyl substituted carbon atoms; the more substituted, the more likely is cleavage. This is a consequence of the increased stability of a tertiary carbon atom over a secondary, which in turn is more stable than a primary. CH3+ < RCH2+ < R2CH+ < R3C+ 31
  • 32. STEVENSONS RULE: Spectroscopy Spectroscopy When an ion fragments, the positive charge will remain on the fragment of lowest ionization potential. Generally the largest substituent at a branch is eliminated most readily as a radical, presumably because a long chain radical can achieve some stability by delocalization of the lone electron. Ex- cleavage of 1-methyl pentane 1-methyl pentane largest fragment In this fragmentation, positive charge remains on the more high substituted fragments, i.e. the one with lower ionization potential. 4. Double bonds, cyclic structures and especially aromatic or hetero aromatic rings stabilize the Molecular ion and thus increase the probability of its appearance. 32
  • 33. Spectroscopy 5. Double bonds favour allylic cleavage and give the Spectroscopy resonance stabilized allylic carbonium. Ex: Mass spectrum of 1-butene 6. Saturated rings tend to lose alkyl side chains at the α carbon atom. This positive charge tends to stay with the ring fragment. Ex: Mass spectrum of n-propyl cyclohexene 33
  • 34. Spectroscopy Spectroscopy 7. In alkyl substituted aromatic compounds, cleavage is very probable at the bond β to the ring, giving the resonance stabilized benzyl ion or more likely, the tropylium ion: Ex: mass spectra of n-butyl benzene. 8. Cleavage is often associated with elimination of small, stable, neutral molecules such as carbon monoxide, olefins, water, ammonia, hydrogen sulphide, hydrogen cyanide, mercaptans, ketone, or alcohols, often with rearrangement. 34
  • 35. Spectroscopy Spectroscopy Factors influencing Fragmentation process: 1.     Bombardment energies 2.     Functional groups 3.     Thermal decomposition 35
  • 36. Spectroscopy Spectroscopy General modes of fragmentation: Fragmentation of the molecular ion takes place in following modes: * Simple cleavage 1. Homolytic cleavage 2. Heterolytic cleavage 3. Retro Diels-Alder reaction * Rearrangement reactions accompanied by transfer of atoms. 1. Scrambling 2. Mc Lafferty rearrangement 3. Elimination 36
  • 37. Spectroscopy Spectroscopy 1. Homolytic cleavage :  Here fragmentation is due to electron redistribution between bonds.  R ─ CH2 ─ CH2 ─ R' R ─ CH2 : CH2 ─ Rꞌ e- R ─ CH2+. + CH2 ─ R' 37
  • 38. Spectroscopy Spectroscopy 2. Heterolytic cleavage: Fragmentation by movement of two electrons: In this type of cleavage both the electrons of the bond are taken over by one of the atoms; the fragments are an even electron cation and a radical with the positive charge residing on the alkyl group. It is designated by a conventional arrow (↶ or ↷) to signify the transfer of a pair of electrons in the direction of the charged site. 3. Retro Diels-Alder reaction: Elimination by multiple σ bond rupture: cyclohexene is broken down to Diene and Dienophile. It can be explained by one or two electron mechanism. 38
  • 39. Spectroscopy Spectroscopy One electron mechanism: Two electron mechanism: * Rearrangement reactions accompanied by transfer of atoms: 1. Scrambling: Fragmentation giving rise to stable carbocation: In certain cases fragmentation takes place at bond, which gives stable carbocation. Ex- Molecular ion from the alkyl benzene undergoes fragmentation at the benzylic bond and final product is seven membered cyclic ion known as Tropylium ion. 39
  • 40. Spectroscopy Spectroscopy 2. Mc Lafferty rearrangement: Fragmentation due to rearrangement of Molecular or Parent ion: Here cleavage of bonds in Molecular ion is due to the intramolecular atomic rearrangement. This leads to fragmentation whose origin cannot be described by simple cleavage of bonds. When fragments are accompanied by bond formation as well as bond for breaking, a rearrangement process is said to have occurred. Such rearrangement involves the transfer of hydrogen from one part of the molecular ion to another via, preferably, a six-membered cyclic transition state. This process is favoured energetically because as many bonds are formed as are broken. 40
  • 41. Spectroscopy Compounds containing hydrogen atom at position gamma to Spectroscopy carbonyl group have been found to a relative intense peak. This is probably due to rearrangement and fragmentation is accompanied by the loss of neutral molecule. This rearrangement is known as McLafferty rearrangement. The rearrangement results in the formation of charged enols and a neutral olefins. To undergo McLafferty rearrangement, a molecule must posses a. An appropriately located heteroatom (ex.oxygen) b. A double bond c. An abstractable Hydrogen atom which is γ (gamma) to C=Osystem. 41
  • 42. Spectroscopy Spectroscopy Table for the common McLafferty peak in the spectra of carbonyl group. Compound type Substituent McL peak (R) Aldehyde -H 44 Methyl ketone -CH3 58 Amide -NH2 59 Acid -OH 60 Ethyl ketone -CH2CH3 72 Methyl ester -OCH3 74 42
  • 43. Spectroscopy Spectroscopy 3. Elimination: Fragmentation due to loss of small molecule: Loss of small stable molecules such as H2O, CO2, CO,C2H4 from molecular ion during fragmentation. Ex- An alcohol readily looses H2O molecule and shows a peak 18 mass units less than the peak of molecular ion. Fragmentation adjacent to the branching point: In case of branched alkanes, bond fission takes place adjacent to the branching point. Hence this leads to the formation of more stable carbocation Ex: 3-methyl pentane 43
  • 44. Spectroscopy Spectroscopy FRAGMENTATION PATTERNS AND FRAGMENTATION CHARACTERISTIC RELATION TO PARENT STRUCTURE AND FUNCTIONAL GROUPS: 1. Saturated Hydrocarbons- a. Straight chain compounds: Following are the features of the mass spectra of Alkanes.  The relative height of the parent peak decreases as the molecular mass increases in the homologous series.  The Molecular ion peak (although weak) is normally present.  The spectra generally consist of clusters of peaks separated by 14 mass units corresponding to differences of CH2 groups.  The largest peak in each cluster represents CnH2n+1 fragment. This is accompanied by CnH2n and CnH2n-1 fragment corresponding to the loss of one and two H atoms respectively. 44
  • 45. Spectroscopy Spectroscopy b. Branched Chain Hydro Carbons:  Greater the branching in Alkanes less is the appearance of the molecular ion and if it appears, intensity will be low.  Bond cleavage takes place preferably at the site of branching. Due to such cleavage, more stable secondary or tertiary carbonium ions results.  Generally, largest substituent at a branch is eliminated readily as a radical. The radical achieves stability by the de- localization of lone electron.  Greater number of fragments results from the branched chain compound compared to the straight compound. This is due to greater pathways available for cleavage. 45
  • 46. Spectroscopy Spectroscopy 2.ALKENES: The molecular ion of alkene containing one double bond tends to undergo allylic cleavage i.e. at the beta bond without the double bond and gives resonance structure. · The molecular ion peak in the spectra of unsaturated compounds is more intense than the corresponding saturated analogues. The reason is the better resonance stabilization of the charge on the cation formed by the removal of one of the π-electrons. · The relative abundance of the molecular ion peak decreases with increase in molecular mass. · The cyclic olefine also shows group of peaks which are 14 mass units apart. ·The general mode of fragmentation is the allylic cleavage. ·The fragments formed by Mc Lafferty rearrangement are more intense. Ex: 1-pentene. 46
  • 47. Spectroscopy Spectroscopy Cycloalkenes usually show a distinct molecular ion peak. A unique mode of cleavage is a type of Retro Diels-Alder reaction. The fragmentation mode involves the cleavage of two bonds of a cyclic system resulting in the formation of two stable unsaturated fragments in which two new bonds are formed. Aromatic compounds:   It shows prominent mol ion peak, as compared to the alkanes and alkenes containing same number of C atoms. This is as a result of the stabilizing effect of the ring.  In these compounds M++1 and M++2 are also noticed, due to C13. If aromatic ring is substituted by an alkyl groups a prominent peak is formed at m/z91. Here benzyl (C6H5C+H2) cation formed rearranges to tropylium cation (C7H7+). This may eliminate a neutral acetylene molecule to give a peak at m/e 65. 47
  • 48. Spectroscopy Spectroscopy Ex: Ethyl benzene Alcohols:  The molecular ion peak of 1º and 2ºalcohol is usually of low abundance. It is not detected in 3º alcohols.  The fragmentation modes in alcohols depend upon the fact whether it is 1º, 2º or 3º alcohols.  The fragmentation of C-C bond adjacent to oxygen atom is the preferred fragmentation mode i.e. α cleavage.  1º alcohols shows M-18 peaks, corresponding to the loss of water.  Long chain members may show peaks corresponding to successive loss of H radicals at M-1, M-2 and M-3.  The CH2=OH is the most significant peak in the spectra of 1º alcohols.  Secondary alcohols cleave to give prominent peaks due R-CH=OH at m/z=45,59,73. 48
  • 49. Spectroscopy Spectroscopy Aromatic alcohols: The relative abundance of the parent ion of aromatic alcohols is large. Some of the fragment modes of benzyl alcohol are loss of one, two or three hydrogen atoms M+H fragment of Benzyl alcohol also rearranges to form hydroxy tropylium ion. The OH group in the Benzyl positions fragments in a way, which favors charge retention on the aryl group. Phenols: The molecular ion peak is intense. The peak due to the loss of hydrogen radical, M+ - H is small. The fragment ion due to the loss of carbon monoxide is significant. Cresols form very intense peak due to the formation of hydroxyl tropylium ion. 49
  • 50. Spectroscopy Spectroscopy Aldehydes The Molecular ion peak of aliphatic Aldehydes is weak. Aromatic Aldehydes shows moderate intense peak. R-CH=O+ R-C≡O+ + H+ Characteristic feature of Aldehyde (especially Aromatic Aldehyde) is loss of α hydrogen. Second common feature of Aliphatic Aldehyde is β cleavage. For ex, Aldehyde with CH2-CHO end group gives rise to characteristic M-43 peaks. Ketones:  Molecular ion peaks are intense than Aldehyde.Most of the abundant ions in the mass spectra of Ketones can be accounted by α cleavage and Mc Lafferty rearrangement. 50
  • 51. Spectroscopy Spectroscopy Nitro Compounds: Aliphatic Nitro compounds fragment by loss of NO2 to give strong carbonium ion. R-NO2+ R+ + NO2 An Mc Lafferty rearrangement occurs but such type of peaks are weak. Nitrites show β cleavage . Aliphatic acids:  The molecular ion peak in aliphatic acids is less intense as compared to that of aromatic acids.Carboxyl group is directly eliminated by α cleavage and a signal is formed at m/e 45.  If α carbon atom is not substituted in aliphatic acids containing a gamma hydrogen atom, Mc Lafferty rearrangement ion is formed at m/e 60. It is often the base peak.  In short chain acids, M-OH and M-COOH peaks are prominent. 51
  • 52. Halogen Compounds: Spectroscopy Spectroscopy  A compound with 1 chlorine atom gives a M+2 peak, which is one third the intensity of the molecular ion peak due to the presence of Molecular ion containing 37Cl isotope.  In a mono bromo derivative the M+2 peak is almost of equal intensity to the molecular ion and is due to the presence of molecular ion containing 81Br isotope.  Fluorine and Iodine being mono isotopic do not give these patterns.  Aliphatic chlorine compounds fragment mainly by the loss of HCl to give peaks at M-36 and M-38. HCl peaks can also be seen at m/z 36, 38.  The relative abundance of the Molecular ion decreases with increase in chain length and increase in branching. 52
  • 53. Ethers: Spectroscopy Spectroscopy  Aliphatic ethers undergo facile fragmentation and exhibit a weak molecular ion peak because the resultant ion is highly stabilized by resonance.  The major fragmentation modes occur through α and β cleavages  α cleavage : Cleavage of a bond α to oxygen occurs, the positive charge being retained on the carbon rather than on oxygen.  β cleavage: A heteroatom induces cleavage at a bond β to it. Such a cleavage favors the loss of larger group as a radical. The ion undergoes further fragmentation to give the series of ions. Ex: Diethyl ether. Aromatic Ethers:  The Molecular ion peak of aromatic ether is prominent. Primary cleavage occurs at the bond β to the ring and first formed ions can decompose further. 53
  • 54. Spectroscopy Spectroscopy IMPORTANT QUESTIONS: 1. State the basic principles of mass spectroscopy. Write about different types of ions produces in a mass spectrometer. What are the general rules for fragmentation pattern in molecules. (2010).20 marks. 2. What are the general rules predicting prominent peaks in a mass spectrum.(Oct’2009).10 marks. 3. Outline principle of mass spectrometry.(2003,2004)10 marks 4. Explain rules of fragmentation in mass spectroscopy with one example each.(2006).10marks. 5. With an example concept of ring rule.(2006).5marks.
  • 55. Spectroscopy Spectroscopy References: 1. Sharma Y.R. Elementary organic spectroscopy principles and chemical applications. 1st ed. S. Chand and Company ltd; New Delhi :2008. 5. Chatwal G.R, Anand S.K. Instrumental methods of chemical analysis. 1st ed. Himalaya Publishing house; Mumbai: 2004. 5. S. Ravi Shankar. Text book of pharmaceutical analysis. 3rd ed. Rx publication; Tirunelveli: 2006. 6. Skoog DA, West DM. principle of instrumental analysis. 2 ed edition 55

Hinweis der Redaktion

  1. 02/11/13
  2. 02/11/13
  3. 02/11/13
  4. 02/11/13