Question

Keto-enol tautomerism is not observed in

• A. CH\(_3\)COCH\(_2\)COCH\(_3\)
• B. C\(_6\)H\(_5\)COCH\(_2\)COCH\(_3\)
• C. C\(_6\)H\(_5\)COCH=CH\(_2\)
• D. C\(_6\)H\(_5\)COC\(_6\)H\(_5\)

Hint:

For tautomerism to occur, there must be at least one \(\alpha\)-hydrogen atom relative to the carbonyl group.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Keto-enol tautomerism involves the interconversion of a ketone (or aldehyde) and an enol. It requires the presence of an \(\alpha\)-hydrogen atom (a hydrogen atom attached to the carbon adjacent to the carbonyl group).

Step 2: Detailed Explanation:
• (A) CH\(_3\)COCH\(_2\)COCH\(_3\): Contains \(\alpha\)-hydrogens, shows tautomerism. • (B) C\(_6\)H\(_5\)COCH\(_2\)COCH\(_3\): Contains \(\alpha\)-hydrogens (on the -CH\(_2\)- group), shows tautomerism. • (C) C\(_6\)H\(_5\)COCH=CH\(_2\): This is an enone. The \(\alpha\)-carbon is the one attached to the carbonyl, but the question is likely checking for a compound without \(\alpha\)-H. While it can tautomerize under certain conditions, the absence of an \(\alpha\)-hydrogen in the ketone form is key. • (D) C\(_6\)H\(_5\)COC\(_6\)H\(_5\): Benzophenone. The carbon atom directly attached to the carbonyl (the carbonyl carbon itself) has no \(\alpha\)-hydrogens attached to it (it is attached to two phenyl rings). Therefore, keto-enol tautomerism is not possible.

Step 3: Final Answer:
Keto-enol tautomerism is not observed in C\(_6\)H\(_5\)COC\(_6\)H\(_5\), which corresponds to option (D).