The document discusses the McLafferty rearrangement, which is an intramolecular atomic rearrangement during fragmentation that results in rearrangement ions. To undergo a McLafferty rearrangement, a molecule must possess an appropriately located heteroatom like oxygen or nitrogen, a π system usually a double bond, and an abstractable hydrogen atom next to the carbonyl system. Rearrangement peaks can be identified by considering whether the mass number of the fragment ion is even or odd relative to the molecular ion.

1. McLafferty rearrangement
Prepared By :
Mahendra G S
M-Pharm,Pharmaceutical
Chemistry
JSSCP, MYSURU

2. Rearrangement
 Rearrangement ions are fragments whose origin
cannot be described by simple cleavage but are a
result of intramolecular atomic rearrangement
during fragmentation.
 Rearrangement involving migration of H-atoms in
molecule that contain a heteroatom.

3. McLafferty rearrangement

4. To undergo McLafferty rearrangement..
 A molecule must posses an appropriately located
heteroatom (eg.,O,N)
 A π system ( usually a double bond)
 And an abstractable H – atom γ to the C=O system

5.  Rearrangement peaks can be recognized by
considering the mass(m/z) number.
 a simple cleavage of ,(no rearrangement)
 even-numbered molecular ion gives an odd
numbered fragment ion
Odd-numbered molecular ion gives an even
numbered fragment ion.

6.  Rearrangement peaks may be recognized by
considering the corollary to the “nitrogen rule”
 Thus ,an even-numbered molecular ion peak derived
from an even-numbered molecular ion is a result of
two cleavage, which may involve a rearrangement.

7. References
 Spectrometric identification of organic compound-
sixth edition, page no:14-15