This document discusses fragmentation techniques in mass spectroscopy. It begins by defining mass spectroscopy as a technique used to determine molecular weight of compounds. The key points made are: 1) Molecular ions formed during ionization undergo fragmentation into smaller daughter ions. 2) Fragmentation occurs through simple cleavage like homolytic, heterolytic, or semi-heterolytic cleavage or through rearrangement reactions like elimination, ortho, or McLafferty rearrangements. 3) Specific fragmentation patterns can provide information about functional groups present like aldehydes producing m/z 44 ions or ketones producing m/z 58 ions.

1. FRAGMENTATION TECHNIQUES IN MASS
SPECTROSCOPY
Presented by:
Sk.Samiya,
1st year M-Pharm,(Pharmacology)
Hindu College of Pharmacy

2. Mass spectroscopy
Definition:
It is a powerful analytical technique useful for determination of
molecular weight of compound.
Principle:
 Initially in mass spectroscopy the sample must be converted into
vapourised or gaseous form then it undergo ionization to form a
molecular ion with the liberation of 1e-.
 This molecular ion normally undergoes fragmentation to form several
fragmented ions or daughter ions.

3. FRAGMENTATION
 The process of breaking up of molecular ion into smaller or daughter
ions is known as “fragmentation”.
 The molecular ion commonly decomposes to a pair of fragments,
which may be either a radical with an ion or a small molecule & a
radical cation.

4. Fragmentation process
 Bombardment of molecules by a 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 50-7ev,
these molecular ions acquire a high excitation resulting in their
break down into various fragments.

5. General modes of fragmentation
Fragmentation of the molecular ion takes place in following mods:
 Simple cleavage
1. Homolytic cleavage
2. Heterolytic cleavage
3. Semi heterolytic cleavage
 Rearrangement reactions
1. Elimination reactions
2. Ortho reaction
3. Mc-lafferty rearrangement

6. Simple cleavage:
Transfer of electrons takes place
1. Homolytic cleavage
 In hemolytic cleavage the electrons are equally transferred to both
atoms & it forms radical and cation.
R
H2C
CH
CH2
R
H2C
CH
CH2
R
+
CH
HC
CH2
IONISATION
HOMOLYTIC
CLEAVAGE

7. 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.
C4H9I
ionisation
CH3
CH2
+ I
C4H9I
HETEROLYTIC
CLEAVAGE

8. 3.Semi heterolytic cleavage
 In this one electron bond cleavage takes place resulting in formation
of radical & cation.
C
H
H H
H
C
H
H H
H
CH3
+
H
IONISATION CLEAVAGE

9. Rearrangement reaction
 It involves the cleavage of bonds and formation of new bonds i.e., it
requires changes to at least two bonds.
 So the produced ions are not structural units of precursors.
 Generally rearrangement leads to loss of smaller molecules.

10. 1. Elimination reaction
 In his fragmentation hydrogen is obstructed by hydroxyl group or
halogen or acetate functional groups results in the elimination of water
or neutral molecule.
R – CH2 – CH2 –CH2 R – CH2 – CH2 – CH2 +
OCOCH3 OCOCH3
CH3COOH + R – CH2 – CH = CH2

11. 2. Ortho effect reaction
 In the case of substituted aromatic compounds the substitute & carbon come into
proximity has help in elimination of neutral molecule. This effect is called ortho
effect.
O
O
CH3
CH3
O
O
CH3
C
H2
C
O
CH2
+
OCH3
H
C
C
C
O
CH2
+ CH3OH
methyl 2-methylbenzoate
methyl 2-methylbenzoate ion
(6-methylenecyclohexa-2,4-
dienylidene)methanone
H

12. 3. Mc-Lafferty rearrangement reaction
 The loss of an alkene fragment by cyclic rearrangement of a carbonyl
compounds ( like aldehyde, ketones, acids, esters, amines),
unsaturated compounds with γ-hydrogens undergo Mc-Lafferty
rearrangement.
Or
 It involves the migration of γ-hydrogen atom followed by cleavage
of β-bond then rearrangement leads to the elimination of neutral
molecule.

13. Mechanism
Fragmentation takes place only at γ-hydrogen
Then this hydrogen is obstructed by oxygen of carbonyl group or
unsaturated compound.
Carbonyl group is converted to hydroxyl group
Bond break down between α & β carbons resulting in liberation of 2e-’s
then rearrangement takes place to form a simple alkene.

14. H
H2C
C
H2
CH2
C
HO
butyraldehyde
H
H2C
C
H2
CH2
C
HO
H2C
C
H
CH
C
HHO
CH2
CH2
+
OH
C
CH2
H
O
C
CH3
H
H
H2C
C
H2
CH2
C
HO
IONISATION
EXAMPLE: Aldehyde
If m/z value is 44(24+4+16) that indicates aldehyde is present and connected to C3 chain.

15. H
H2C
C
H2
CH2
C
CH3O
H
H2C
C
H2
CH2
C
CH3O
H2C
C
H
CH2
CH
CH3HO
CH2
CH2
+
CH2
C
CH3HO
CH3
C
CH3O
H
H2C
C
H2
CH2
C
CH3
O
pentan-2-one
ionisation
If m/z value is 58 (36+16+6) that indicates the compound containing ketone group
attached to C3 chain
Ex:- ketone

16. H
H2C
C
H2
CH2
C
NH2O
H
H2C
C
H2
CH2
C
NH2O
H2C
C
H
CH2
CH
NH2HO
CH2
CH2
+
CH2
C
NH2HO
CH3
C
NH2O
butyramide
H
H2C
C
H2
CH2
C
NH2O
ionisation
Ex:-Amides
If m/z value is 59 (24+16+14+5) that indicates the compound containing amide group
attached to C3chain

17. REFERENCES:
 Instrumental methods of chemical analysis- B.K Sharma,
 Instrumental methods of analysis By Chatwal,
 Principles of Instrumental analysis By Donglas Skoog