Rearrangement reactions involve the migration of an atom or group within the same molecule. A 1,2-shift is a migration from one atom to an adjacent atom. The Favorskii rearrangement involves the rearrangement of cyclopropanones and α-halo ketones in the presence of a base, forming carboxylic acids or derivatives. For cyclic α-halo ketones, the Favorskii rearrangement causes a ring contraction from a 6-membered to a 5-membered ring.

1. Rearrangement reactions
• One atom or a group moves from one
atom to another within same molecule
• Migration from a atom to adjacent atom
is called 1,2-shift.
Listen Carefully

2. Favorskii Rearrangement
• Rearrangement of cyclopropanones and
α- halo ketones, which leads to formation
of carboxylic acids, or carboxylic acid
derivatives.
RCH2 C CH2Cl
BASE RCH2 CH2COO-
O
Listen Carefully

3. Hydroxide(OH) Carboxylic Acid(-COOH)
Amine (NH2) Amide -CONH2
Alkoxide(-OR) Ester(-COOR)
Listen Carefully

4. OH
Base
O
Cl
Cyclic α-halo ketones, the Favorskii
rearrangement constitutes a ring
contraction.
6-Membered 5-Membered
Listen Carefully

5. Mechanism of Cyclic α-halo ketone-
Listen Carefully

6. OH
Base
O
Cl
When there is a group on non-halogenated
alpha position

7. •When there is no α-Hydrogen
then migration of the group will
take place
Listen Carefully

8. Mechanism
Listen Carefully