The effect of steric hindrance on the S_RN1 reaction of some α-Alkyl-p-nitrobenzyl chlorides

Abstract

The reactions of a series of α-substituted p-nitrobenzyl chlorides, p- NO₂C₆H₄CH(Cl)R (R = Me, Et, Pr^t, Bu^t), with the lithium salt of 2- nitropropane in dimethyl sulphoxide and dimethylformamide have been studied. When R = Me or Et, competing S_RN1 and S_N2 processes take place, giving C- and O-alkylated products respectively. In the more sterically hindered cases where R = Prⁱ or Bu^t, the only reaction taking place has been shown to be an S_RN1 reaction with exclusive O-alkylation. These observations indicate that the S_RN1 reaction is prone to steric hindrance, and that radical alkylation of the ambident nitronate ion occurs on the more accessible oxygen atom in sterically hindered situations.