LACK OF ENHANCed REACTIVITY OF α-NUCLEOPHILES In THE S_N2 REACTIONS OF BENZYL BROMIDES AND SMALL α-EFFECT In THE MICHAEL ADDITION RECTION OF AMIDES TO P-TOLYL VINYL SULFONE

Abstract

Both second-order rate constants of S_N2 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 sp³carbon this may be due to the lack of tight σ-bond formation at the transition state. A very small positive deviation from the Brønsted plots was observed in the Michael addition of hydrazine and other amines to p-tolyl vinyl sulfone. This may be due to the small β-value associated with the reaction.

Key Words:

• Vinyl sulfone
• Michael addition
• hydrazine
• Brønsted plots