Aromatic Electrophilic Substitution VIII [1]. Ortho Effects in the Iododestannylation of Phenyltrialkyltins

Abstract

It is shown that one ortho methyl group has a weaker accelerating effect than a para methyl group in the iododestannylation of phenyltrialkyltins, whatever the size of the alkyl chains bound to the tin atom. Two ortho methyl groups lead to a rate which is exactly that calculated assuming additivity of the effects, when the leaving group is Sn(CH3)3. If Sn(nPr)3 is the leaving group, 2, 6‐disubstitution leads to a small but significant increase in rate. The results are interpreted in terms of overcrowding in the reactant, and of relief of strain in the transition state; the observed effects are however smaller here than in the case of similar silicon derivatives, and the difference is attributed to the difference in carbon‐metal bond lengths.