Wagner

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.
C CCC
R(H)R(H)
+
+
1
1' 2'
1
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. Wagner-Meerwein rearrangement as a part of
an isomerizing E1 elimination
OH
H H
OH2 H
H
conc. H2SO4
_ H2O
_
H+
+
+
+
Methyl shift
♦ Example:

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. CH3 C
CH3
CH3
CH2
CH3 C
CH3
CH2CH3
H+
H2O
CH3 C
CH3
CH2CH3
OH
CH3
CH3
CH3
CH2
NH2
HNO2
CH3
CH3
CH3
CH2
NH2
HNO2
CH3 C
CH3
CH2CH3
OH
Mechanism
Methyl shift
+
+
♦ Example:

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