Question

Among the given compounds, which can exhibit tautomerism ?

• A. $I$ only
• B. $II$ only
• C. $III$ only
• D. All of the above

Answer 1

The correct option is B $II$ only

Conditions for tautomerism :
1. If a carbonyl compound having an H atom at its $s{p}^3$ hybridised $\alpha$-C atom
2. If an $\alpha ,\beta$ unsaturated carbonyl
compound contains a $\gamma$-H at its $s{p}^3$
hybridized $\gamma$-C atom.
Only in structure $II$, $\alpha$-Hydrogens attached to $s{p}^3$ hybridised carbons are present.
This is not the case in structure $I$ and $III$
Enol form of structure $II$ (as given below), is aromatic and thus stable.