Chemistry - GOC Question with Solution | TestHub

Deprotonation at carbon 4 gives an anion that is allylic to the C₂=C₃ double bond, which is itself conjugated with the carbonyl group : the charge delocalises over the whole O=C-C=C-C system and finishes on the carbonyl oxygen (a dienolate, charge on O). Deprotonation at carbon 5 gives an anion stabilised only by the nitrile (charge on N at best). Carbons 2 and 3 are vinylic and have no acidic protons. Oxygen stabilises the charge far better than nitrogen, so carbon 4 is deprotonated first.