Theory of Induced Polarities in Benzene

Abstract

RECENTLY in this periodical, Lapworth and Robinson¹ gave a criticism of the theory developed by Erich Hückel² of the induced polarities in benzene. This criticism referred mainly to three points, which may be shortly reviewed here. (For the details see the note of Lapworth and Robinson.) First, the authors claim that any theory of the influence of groups on the course taken by substitution in benzene must be able to correlate this influence with the influence of the groups on the additive reactions of unsaturated compounds, since these reactions are said to obey the same laws as those that govern aromatic substitution, although in the case of substitution a hydrogen atom^* is expelled, which does not occur in the case of addition. Secondly, they correlate the influence of the different groups on the strength of binding of the H-atoms in benzene with the influence of such groups on the relative strengths of acids and bases. From this correlation they derive certain contradictions. Thirdly, they direct attention to the fact that in certain cases of substitution the loss of the hydrogen atom may happen at some other carbon atom than that which is to be the point of attachment of the new substituent.