Lack of enhanced reactivity of α-nucleophiles in the SN2 reactions of benzyl bromides and small α-effect in the Michael addition reaction of amides to P-tolyl vinyl sulfone

Both second-order rate constants of S(N)2 reactions on benzyl bromide and p-nitrobenzyl bromide with hydroxy nucleophiles and those of the Michael addition reactions of a few amines to p-tolyl vinyl sulfone have been determined. The values of k(HOO)-/k(HO)- for benzyl and p-nitrobenzyl bromide were very small, i.e., 1.3 and 1.2 respectively; in the S(N)2 reaction on sp(3) carbon this may be due to the lack of tight sigma-bond formation at the transition state. A very small positive deviation from the Bronsted plots was observed in the Michael addition of hydrazine and other amines to p-tolyl vinyl sulfone. This may be due to the small beta-value associated with the reaction.