The influence of the nitro-group upon side-chain reactivity. Part IV. The inhibition of α-proton extraction from 4-nitrobenzyl chloride by the steric effect of methyl groups in the 3- and 5-positions

Abstract

The fast α-proton extraction from 4-nitrobenzyl chloride by alkali in dioxan, leading to the formation of 4,4′-dinitrostilbene by the α-E1cB mechanism (the rate-determining step is formation of a carbene intermediate), is greatly retarded by one methyl group in the 3-position and completely inhibited by two methyl groups in the 3- and 5-positions; instead, alcohols and ethers are formed by the S_N2 displacement of the halogen by the alkali and by the formed alkoxides. Kinetic investigations, and evaluation of the Arrhenius parameters, on the chlorides with the alkali in dioxan, alone or in presence of added alkoxides, demonstrate clearly the steric effect of the methyl groups. Infrared and ultraviolet spectra of the chlorides and related structures throw much light on the results.