GURU NANAK INSTITUTE OF PHARMACEUTICAL
SCIENCE AND TECHNOLOGY
MASS FRAGMENTATION OF CARBONYL COMPOUNDS
PRESENTED BY
 MOHAMMAD JAVED
 008
 M.PHARM(PHARMACEUTICAL CHEMISTRY)
 SUBJECT-ADVANCED SPECTRAL ANALYSIS
 SUBJECT CODE-MPT 2031

INTRODUCTION
 In mass spectrometry, fragmentation is the dissociation of energetically unstable molecular ions
formed from passing the molecules mass spectrum.
 These reactions are well documented over the decades and fragmentation pattern is useful to
determine the molar weight and structural information of the unknown molecule.
 A mass spectrum will usually be presented as a vertical bar graph, in which each bar represents an
ion having a specific mass-to-charge ratio (m/z) and the length of the bar indicates the relative
abundance of the ion. The most intense ion is assigned an abundance of 100, and it is referred to as
the base peak.

1.ALDEHYDES
A) ALIPHATIC ALDEHYDE-
• Gives weak molecular ions.
• The most common fragmentation pattern are – alpha cleavage, beta cleavage and Mc-Lafferty
re-arrangement.
ALPHA-CLEAVAGE BETA-CLEAVAGE MC-LAFFERTY
REARRANGEMENT
Most prominent To a small extend Gamma hydrogen present

Now let see the fragmentation pattern of BUTANAL
A) ALPHA-CLEAVAGE-
B) BETA-CLEAVAGE-

C) Mc-Lafferty of Butanal-

B) AROMATIC ALDEHYDE-
 Here Alpha-cleavage is the prominent mode of fragmentation.(C-H BOND BREAKAGE)
 Lets take a example of Benzaldehyde.

2.KETONE
 M+ generally strong
 α-cleavage is the primary mode of fragmentation
 β-cleavage less common, but sometimes observed
 McLafferty rearrangement possible on both sides of carbonyl if chains sufficiently long
 Cyclic ketones show complex fragmentation patterns
 Aromatic ketones primarily lose R upon α-cleavage, followed by loss of CO.
Lets take example of 2-pentanone via alpha cleavage and Mc-Lafferty rearrangement method in the
next slide….

MASS SPECTRUM OF 2 PENTANONE

SUMMARY
• Overall, the mass fragmentation of carbonyl compounds can be a complex process that depends on
the specific compound being analyzed and the conditions of the mass spectrometry experiment.
However, by identifying the characteristic fragmentation patterns of carbonyl compounds, it is
possible to use mass spectrometry to identify and analyze these compounds.

REFERENCE
[1] Sharma, Y. R. (2007). Elementary organic spectroscopy. S. Chand Publishing.
[2] Bowie, J. H. (2010). Mass spectrometry of carbonyl compounds. John Wiley & Sons, Ltd EBooks,
277–341. https://doi.org/10.1002/9780470771228.ch5