Question

can you suggest a reason why p-cyanobenzaldehyde does not undergo the benzoin condensatior symmetrical benzoin product?

Answer 1

In the 4-NitrobenzaldehydeNO₂ is the electron withdrawing group soit is deactivated the reactivity of compound.In thebenzoin condensation the CN^- ion attacks on carboncenter which is having +ve charge actually. But here the +ve chargeon carbon center is too small because the NO₂ grouppulls the electrons towards its side.Resulting the nucliophilewhould not attack at carbon center favourably . Hence the reactionis not followed under benzoin condensation.