Mc lafferty rearrangement

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