Elimination Reactions in Organic Chemistry

Abstract

MECHANISM

IN classical organic chemistry, two empirical rules, each of limited application, summarize the regularities which have been observed to govern the formation of olefins from alkyl compounds. Hof-mann's rule (an extendBd form of the rule originally given by Hofmann), applying to primary alkyl groups in ammonium or sulphonium hydroxides, refers to the preferential production of the least alkylated of the possible alkyl ethylenes. Saytzeff's rule, relating to secondary and tertiary alkyl groups in alkyl halides, expresses the predominating formation of the most alkylated of the possible alkyl ethylenes. Having regard to the close analogy of the elimination reactions of ‘onium salts and halides, the contrary tendencies of these two rules is striking. The need for an explanation was strongly emphasized when in 1927 Hofmann's rule was rationalized as a manifestation of the inductive effect1, that is, of a very general type of molecular polarization, which must from its nature oppose the operation ofSaytzeff's rule. We have since been much concerned with the problem of reconciling and rationalizing the two rules, but the work has not been published, because, until comparatively recently, the solution was not established. An outline is now given as it may still be some time before detailed publication is possible.