Wagner-Meerwein rearrangements involve the migration of hydrogen or alkyl groups within carbonium ions during rearrangement reactions. Specifically, they refer to [1,2]-rearrangements of hydrogen or alkyl groups between carbon-1 and carbon-2 in carbonium ions that do not contain heteroatoms attached to these carbon centers. An example of a Wagner-Meerwein rearrangement provided is the neopentyl rearrangement, which involves the migration of a methyl group in a carbonium ion.

1. Rearrangement
Reactions

2. Rearrangement Reaction
The term “rearrangements” is used to
describe organic reactions which
involve the migration of a H atom or
of a larger molecular fragment.
♦ Carbonium ion rearrangement
♦ Carbanion rearrangements
♦ Radical rearrangements

3. Carbonium ion rearrangements
♦ Without change in carbon skeleton
1- Allylic rearrangement
♦ With change in carbon skeleton
1- Neopentyl rearrangement
2- Pinacol-pinacolone rearrangement
3- Wolf rearrangement
4- Rearrangement of hydrocarbons

4. Wagner-Meerwein
rearrangements
♦ The rearrangements involving change in
carbon skeleton are collectively known as
Wagner-Meerwein rearrangements

5. Wagner-Meerwein rearrangements
♦ Wagner-Meerwein Rearrangements are [1,2]-
rearrangements of H atoms or alkyl groups in carbonium
ions that do not contain any heteroatom attached to the
valence-saturated center C-1 or to the valence-unsaturated
center C-2.
1 1
R(H) R(H)
+
C C+ C C
1' 2' 1' 2'

6. Example is neopentyl rearrangement

8. Example:
♦ 1-Bromopropane isomerizes quantitatively to 2-
bromopropane under Friedel-Crafts conditions.
The [1,2]-shift A→B involved in this reaction
again is an H-atom shift.

9. ♦ Example:
Wagner-Meerwein rearrangement as a part of
an isomerizing E1 elimination
+
OH conc. H SO OH2 H
2 4
+
_H O
2 H
Methyl shift
H H
+
_
H+

10. Example
♦ Conversion of p-xylene to m-xylene
In the presence of acid methyl group moves
to meta position, which is energetically
more stable

11. ♦ Example:
CH3 OH
HNO2
H3C CH2NH2 CH3 C CH2CH3
CH3 CH3
Methyl shift
Mechanism
CH3 HNO2 CH3 +
H3C CH2NH2 CH3 C CH2
CH3 CH3
+ OH
CH3 C CH2CH3 H2O CH3 C CH2CH3
CH3 H+ CH3

12. ♦ Amylalcohol is isopentyl alcohol
♦ Tertiarybutyl carbinol is neopentyl alcohol
♦ 2 methyl butanol is amyl alcohol