Chemistry - STRUCTURAL ISOMERISM Question with Solution | TestHub

The compound is cyclohex-3-en-1-one. The alpha positions C-2 and C-6 (2H each, 4H) exchange first. The enol formed at C-2 is conjugated with the ring double bond (O-C=C-C=C), so C-4 acts as a gamma position through this dienol and its hydrogen (1H) also exchanges on prolonged treatment; the enol at C-6 is not conjugated with the $\mathrm{C}=\mathrm{C}$ (an sp3 $\mathrm{C}{\mathrm{H}}_2$ lies between), so the far vinylic hydrogen does not exchange. Total = 4 + 1 = 5.