molecular rearrangement introduction which includes nucleophilic, electrophilic, and free radical rearrangement. and mechanism, applications of favorskki and benzil benzilic acid rearrangement.

1. ORGANIC CHEMISTRY
MOLECULAR REARRANGEMENTS
(FAVORSKII & BENZILIC REARRANGEMENT)

2. REARRANGEMENT
In a rearrangement reaction a group
moves from on atom to another in the same molecule
A Migration origin
B Migration terminus
Most of the rearrangements are migration from an atom the adjacent atom
(1,2 shifts) but some are at long distances
A
W
B B
W
A

3. REARRANGEMENT PROCESS MIGRATORY
GROUP
Electrophilic
or
Cationotropic
Migratory group move
Without it’s lone pair
Electrophile
Nucleophilic
or
Anionotropic
Migratory group move
with it’s electron pair
Nucleophile
Free radical
Rearrangement
Migratory group move
with one electron
Free radical

4. REASON:
They have different types of transition states.
 In the case of nucleophilic migration, two electron in A-W bond overlaps with
the orbital on atom B, which contains zero electrons.
 In the case of free-radical migration, one electron in A-W bond overlaps with
the orbital on atom B, which contains one electron.
 In the case of electrophilic migration, two electron in A-W bond overlaps with
the orbital on atom B, which contains two electrons.
Nucleophilic shifts are much more common than
electrophilic or free radical 1,2 shifts.

5.  The overlap of these orbitals gives rise to three new orbitals, which have an
energy relationship similar to one bonding and two degenerate antibonding
orbitals.
Nucleophilic migration Two electrons involved , both can go into
the bonding orbital which has lower energy
Electrophilic or three or four electrons involved, they
free-radical migration go to the antibonding orbital with
higher energy
 It is not surprising therefore that, when 1,2-electrophilic or free-radical shifts
are found, the migrating group W is usually aryl or some other group that can
accommodate the extra one or two electrons and thus effectively remove them
form the three-membered transition state or intermediate.

6. FAVORSKI REARRANGEMENT
Alexey Favorsky
(1860-1945)

7. Base catalyzed rearrangement of α- haloketone into
carboxylic acid or its derivatives is called favorskii rearrangement.
α- halo ketones carboxylic acid
BASE PRODUCT
ALKOXIDE ION (OR-) ESTER
HYDROXIDE ION (OH-) CARBOXYLIC ACID
AMINE AMIDE

8.  Rearrangement of cyclic ketones results in ring contraction.
 Base abstracts the hydrogen which is α to the carbonyl
group to give carbanion.
 Then they undergo intramolecular SN2 displacement of the
halide reaction to give a cyclo propanone intermediate.
 The cyclo propanone ring is then opened by the base in such
a way as to give more stable carbanaion .
 It subsequently takes up a proton to give the ester or acid or
amide depending upon the base employed.
O
Cl
2chloro cyclo hexanone
O
OH
cyclopentane 1 carboxylic acid
OH-

10. CYCLO α- HALO KETONE MECHANISM

11. APPLICATIONS

12. 1.
2.
3.
4.

13. BENZIL BENZYLIC ACID
REARRANGEMENT
Justus Freiherr von Liebig
(12 May 1803 – 18 April 1873)

14. BENZIL BENZYLIC ACID
(α-diketone) ( α- hydroxy acid)
 When diketone treats with strong base to form corresponding salts of acids
are called Benzil-Benzilic acid rearrangement.
 It can be takes place in aliphatic diketones and α-ketone aldehyde.
 Formation of stable carboxylate salt is driving force for the reaction.
 It is a irreversible reaction.
 Application has been limited only to aromatic α- diketones.
O O
benzil
OHO
OH
benzilic acid
NaOH

15. MECHANISM

16.  The attack of hydroxide ion on carbonyl carbon leads to the formation of
alkoxide ion
Alkoxide ion then undergoes the migration of aryl group to give the rearranged
alkoxide .
It the undergoes proton transfer to give benzilate ion which on hydrolysis gives
benzilic acid.
 In an unsymmetrical diketone the attack of OH- ion takes place at the reactive
carbonyl carbon.
The migration of aryl group will attached to the more reactive carbonyl carbon
When alkoxide or amide anions are used in the place of alkali the corresponding
esters or amides are formed.
This process is called benzilic ester rearrangement.

18. APPLICATIONS

20. THANK YOU