Question

Which among the given molecules can exhibit tautomerism?

• A. III only
• B. Both I and III
• C. Both I and II
• D. Both II and III

Answer 1

The Correct Option is A

Tautomerism is a phenomenon where a chemical compound exists in two (or more) readily interconvertible structures that differ notably in the position of at least one atomic nucleus, usually hydrogen. Generally, this involves the shift of a hydrogen atom between a carbon and a heteroatom. In keto-enol tautomerism, the shifts occur between a carbon atom and an oxygen atom, typically involving an alpha-hydrogen and the carbonyl group.

To determine which molecule can exhibit tautomerism, let's examine each option:

1. Molecule I: This is a cyclic ketone. Cyclic ketones generally do not exhibit keto-enol tautomerism unless there is an alpha-hydrogen available. In this case, the molecule does not have an alpha-hydrogen, so it cannot exhibit tautomerism.
2. Molecule II: This is a diketone with no alpha-hydrogen between the two ketone groups. The absence of an alpha-hydrogen adjacent to the carbonyl groups means it does not exhibit keto-enol tautomerism.
3. Molecule III: This cyclic ketone does have an alpha-hydrogen. It can ionize and transfer between the oxygen and carbon to form a tautomeric enol form. Therefore, this molecule can exhibit tautomerism.

Based on the analysis, Molecule III is the only compound capable of exhibiting tautomerism due to the presence of an alpha-hydrogen.

Thus, the correct answer is III only.