The Effect of Steric Hindrance on Radical and Ionic Substitution Reactions of Nucleophiles with Some α-Alkyl-p-Nitrobenzyl Chlorides

Abstract

The reactions of the α-alkyl p-nitrobenzyl chlorides, p-NO₂C₆H₄CH(CI)R(R = Me, Pr¹, Bu^t), with nucleophiles, e.g, nitrite, nitroethanide, benzenethiolate and p-toluenesulfinate ions and the anion derived from diethyl 2-methylmalonate, in dimethyl sulfoxide have been studied. When R = Bu^t, S_RNl reactions take place and give, in the reaction with p-toluenesulfinate and the anion from diethyl 2-methylmalonate, extremely sterically crowded molecules, which, as a result of bond formation between the more hindered atom in the ambident nucleophile and the benzylic carbon, display dynamic ¹H N.M.R. effects. The derivatives where R = Me or Prⁱ undergo radical and/or ionic processes depending on the nucleophile being used. Pathways accounting for some of the unusual compounds produced, e.g. 5-methyl-3,5-bis(p-nitropheny1)-2-isoxazoline N-oxide and (E)- and (Z)-p-nitroiso-butyrophenone O-(p-nitrobenzoyl) oximes from reaction of nitrite ion with the α-methyl and α- isopropyl compounds respectively, are proposed.