Nomenclature

Introduction
• Organic Chemistry:
Is the branch of chemistry that involves the scientific study of Organic
compounds (compounds that contain covalently bonded carbon atoms).
This branch of chemistry primarily deals with the structure and chemical
composition of organic compounds, the physical and chemical properties
of organic compounds, and the chemical reactions undergone by these
compounds.
• Organic Compounds :
Are hydrocarbons which are made up of carbon and hydrogen
2

Classification of Organic Compounds
Organic compounds
Open chain or acyclic compounds
Ex- butane, ethanol
Closed chain or cyclic compounds
Homocyclic or Carbocyclic compounds Heterocyclic compounds
Aromatic compounds or benzenoides
Ex- benzene, phenol
Follow huckels rule (4+n)
Alicyclic compounds
Ex- cyclopropane, cyclohexane
Aromatic compounds
Or non benzenoid heterocyclic compounds
Ex- Turan, Thiophene (Follow huckels rule (4+n))
Non aromatic Heterocyclic
Ex- THF, Dioxane, piperidine
3

4
Types of Organic Compounds
1.Aliphatic compounds:
Compound which consist of open-chain of carbon atoms are called aliphatic compounds.
There is no limit of the number of atoms involved.
Ex-
Ethane CH3-CH3
Propane CH3-CH2-CH3
Ethyl alcohol CH3-CH2-OH
Acetic acid CH3-COOH
n-butyl amine CH3-CH2-CH2-CH2-NH2

5
2. Saturated and unsaturated compounds:
• Compounds which contain only carbon and hydrogen are called hydrocarbons.
• A hydrocarbon is said to be saturated if it contains only C-C single bonds.
• A hydrocarbon is said to be Unsaturated if it contains C=C or multiple bonds.
Ex-
Ethane
Ethylene
acetylene
The term unsaturated is also sometimes used to describe a compound containing multiple
bonds between other pair of atoms, e.g.
It is saturated
It is unsaturated
It is unsaturated

6
3.Aromatic compounds:
Benzene and all compounds that have structure and chemical properties resembling benzene
are called aromatic compounds.
Each corner
represents
CH group
Benzene Aniline Naphthalene

7
4.Alicyclic compounds:
• Cyclic compound which consist only of carbon atoms are called alicyclic or carbocyclic
compounds.
• Ex-
Each corner
represents
CH group
Cyclopropane Cyclobutane Cyclohexane

8
5.Heterocyclic compounds:
• Cyclic compounds in which the ring atoms are of carbon and some other element For ex- (N , S, O,)
are called heterocyclic compounds
Oxirane
Ethylene oxide
Qunoline
Pyridine

Types of Carbon and Hydrogen atoms
There are four type of carbon atoms:
1. Primary (10) carbon atom
which bonded to one other carbon atom or none.
10
9

2. Secondary (20) carbon atom
which bonded to two other carbon atoms
20
10

3. Tertiary (30) carbon atom
which bonded to three other carbon atom.
30
11

4. Quaternary (40) carbon atom
which bonded to four other carbon atom.
40
12

A system of naming compounds in chemistry, IUPAC
stands for:
IUPAC Nomenclature of Organic Compounds
International
Union of
Pure and
Applied
Chemistry
13

14
GENERAL RULES OF IUPAC SYSTEM:
1.Longest chain rule
• Select the longest possible continuous (not necessarily straight)
chain of carbon atoms.
• The base name corresponds to the number of carbon atoms in the longest chain.
• The full name for the alkane will include the names of any branches.
Longest chain
Alkyl group

15
2.Position of the substiuent
Number of the carbon atoms in the parent chain as 1,2,3…etc. starting from the end
which gives lower number to the carbon atoms carrying the substituents
i.e. Always number from the end of the longest chain closest to the first branch.
C- C- C- C- C- C C- C- C- C- C- C
6
5
4
5
6
X X
Substituent
CORRECT WRONG
1
2
3
2
1 3 4

3.Lowest set of locant rule
When two or more substituents are present, then end of the parent chain
which gives the lowest set of locants is preferred for numbering.
Number the chain so as to give the lowest number possible to the:
• Functional group followed by
• Double bond,
• Triple bond
• Finally the substituent

17
3.Lowest set of locant rule
Ex-
Set-1
Set-2
2 1
5
3
5 4
4
3
2
1

18
So which one is the correct numbering according to the above rule??
Set-1 Or set-2
Carboxylic acid> Sulphonic acid> Anhydride> Ester> Acid
chloride> Acid amide> Nitrile> Aldehyde> Ketone> Alcohol>
Amines> Alkene> Alkyne .
The group higher in the preference series is written as a Suffix While the one
lower to it would be written as a Prefix.
Principal functional group written as a suffix, while others are regarded as
substituents—written as a prefixes.

19
For naming the organic compounds systematically first we have to first
study about the following three features
(a) Root word
(b)Primary suffix
(c)Secondary suffix
(d)Primary Prefix
(e)Secondary prefix
IUPAC name = Prefixes+ Root word + Primary
Suffix+ Secondary suffix

It is the name corresponding to no. of carbon atoms in the longest chain of CARBON
atoms in the organic compound.
To determine the word root we need to learn the table given alongside.
(a) Root word
C1 Meth-
C2 Eth-
C3 Prop-
C4 But-
C5 Pent-
C6 Hex-
C7 Hept-
C8 Oct-
C9 Non-
C10 Dec-
20

(b)Primary suffix
It indicates the nature of the carbon atom chain selected
• Only single bonds between C atoms (also called saturated) -ane
• Presence of double bond between C atoms -ene
• Presence of triple bond between C atoms -yne
If the parent chain contains two, three or more double or triple bonds,
then the numerical prefixes such as di (for two) ,
tri (for three), tetra (for four) , etc. are added to the primary suffix.
21

(b)Primary suffix
Ex:-
-yne
-ene
-ane
butane butene butyne
propane But-2-ene But-2-yne
22

Suffixes that are added after the primary suffixes to indicate the presence of a
particular functional group in carbon chain is called the secondary suffix.
(c) Secondary suffix
Sr.
No
Class of organic compound Functional group Secondary suffix
1. Carboxylic acid -COOH -Oic Acid
2. Esters -COOR -Alkyl…..Oate
3. Acid chlorides -COCl -oly choride
4. Acid amides -CONH2 -Amide
5. Acid ahydride -Anhydride
6. Aldehyde -CHO -al
23

Sr.
No
Class of Organic Compound Functional group Secondary suffix
7. Ketones -one
8. Nitriles -nitril
9. Isocyanides -Isocynide
10. Thiol -Thiol
11. Alcohols -ol
12. Amines Amine
24

Now let us see how the IUPAC names are formed from the Root, Primary suffixes and
the Secondary suffixes.
Sr.
No.
Homologus
Series
Root word Primary Suffix Secondary Suffix IUPAC name
1. Alcohols
(saturated)
Alk -ane -ol Alkanol
2. Alcohols
(unsaturated)
Alk -ene -ol Alkenol
3. Alcohols
(Unsaturated) One triple bond
Alk -yne -ol Alkynol
4. Aldehydes
(saturated)
Alk -ane -al Alkanal
5. Ketones
(saturated)
Alk -ane -one Alkanone
25

(d) Primary Prefix
• It is always be kept in mind that alkyl groups forming branches of the
parent chain are considered as side chains.
• Cyclo is used immediately before the word root in case of alicyclic (but not
aromatic) compounds .
• Root words are profixed with the name of the substituent or the side
chain.
Ex- Primary prefix- cyclo
Root word-hex
Primary suffix-ane
Cyclohexane
26

(c) Secondary Prefix
• Are added before the word root and before the primary prefix in case of carbocyclic
or alicyclic compounds
• Atoms or groups of atoms such as fluoro(-F), Chloro(-Cl) bromo(-Br), Ido(-I),
Nitro(-No2) and Alkoxy(-OR) are referred to as substituents.
Ex- Secondary prefix- 3-bromo
Primary prefix- cyclo
Root word-hex
Primary suffix-ane
IUPAC name = 3-bromocyclohexane-1-ol
27

Arrangement of Prefixes, Root word and Suffixes
These are arranged a follows while writing the name in such a manner.
IUPAC name = Prefixes+ Root word + Primary Suffix+ Secondary suffix
Ex-
1
2 3
4 If we consider the above
example then
1.Prefix= Bromo
2.Root word = But
3.Primary suffix= ane
4.Secondary suffix= oic acid
5.No of Carbons = 4
IUPAC name = 3-bromobutanoic acid
28

Ex-2
5
4
3
2
1
In the above given example
1. Prefix= Methyl
2.Root word = Pent
3. Primary suffix= ene
4. Secondary suffix = ol
5.Number of Carbons = 5
IUPAC name = 4-methylpent-2-en-1-ol
29

Ex-3
In the above given example
1.Prefix = Methyl
2.Root word = Pent
3.Primary suffix = yne
4.Secondary suffix = oic acid
1
2
3
5
4
IUPAC name = 4-methylpent-2-ynoic acid
30

Ex-4
3
2
1
IUPAC name = 2-methylpropan-2-ol
1.Prefix = Methyl
2.Root Word = Prop
3.Primary Suffix = ane
4.Secondary Suffix = ol
31

1 3
2 4
2,2-dimethylbutane
1
2
3
2,2-dimethylpropane
1
2
3
4
2-methylbut-2-ene
1
2
3
4
but-1-yne
1
2
3
4
3-methylbut-1-yne 3-methylpent-1-ene
1
2
3
4
5
32

1 3
2
propan-1-ol propan-2-ol
1 1
2
2
3 3
2,2-dimethylpropan-1-ol
1
2
Ethanoic acid
1
2
3
4
2-methylbutanoic acid pentan-3-one
1
2
3
4
5
33

Nomenclature

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