91Ó°ÊÓ

The process of enlarging the size of the ring is known as the ring expansion and is a type of rearrangement reaction (a special type of rearrangement of carbocation).

The ring enlargement process is mainly required in the 3,4-memberedring due to the presence of maximium angle strain.

The reaction of cyclohexanone with diazomethane in which the diazomethane acts as the nucleophile attacks the carbonyl carbon of cyclohexanone formation of the tetrahedral intermediate immediately loses the stable nitrogen atom$\left({\text{N}}_{\text{2}}\right)$, resulting in the formation of acarbocation.

Finally, carbon from the ring gets attached to the carbocation resulting in the ring expansion and formation of the given product, cycloheptanone.

The mechanism of forming the cycloheptanone is shown as follows:

Formation of cycloheptanone