Question

Which reaction give cyclic ketone as a product?
A.

B.

C.

D.

Answer 1

Hint: We know that the cyclic acetals are generally formed when the reaction between the two molecules i.e. a ketone and a diol take place. This reaction results in the formation of two main products i.e. a ketal and water.

Complete answer:
Cyclic acetals or cyclic acetals are more stable in comparison to acetals because of the presence of chelate effect that is majorly derived from having both groups of acetals being connected to each other in diol. Cyclic acetals have their major applications in carbohydrate chemistry. alkyl groups are close enough then we have the possibility of them interacting with each other and these reactions occur when the dicarboxylic are heated. When dicarboxylic acids are heated, they tend to undergo cyclization to form cyclic ketone. But for cyclization to happen the ring formed should not have strain which means that five and six membered rings are the most favored because of their least angle strain. Now in our question the first compound cannot undergo cyclization because a ring of two carbon atoms is not possible. Compound A which on cyclization will give a six membered ring which is stable, so this compound is capable of undergoing cyclization and will give cyclic ketone as shown below:

Therefore, the correct answer is option A.

Note:
Remember that a ketal refers to a functional group that has been derived from a ketone with the replacement of a carbonyl $\left( C=O \right)$ group by two alkoxy groups. In other words, a ketal can also be referred to as an acetal derived from the ketone. Therefore, a cyclic ketal is a ketal in which ketal carbon along with one or both oxygen atoms are members of a ring.