Aromatic reactivity. Part LIX. Substituent effects of groups of type CH2Y in acid cleavage of p-YCH2·C6H4SiMe3compounds and on the charge-transfer maxima of YCH2Ph–tetracyanoethylene complexes

Abstract

The rates of cleavage of p-YCH₂·C₆H₄·SiMe₃ compounds by a mixture of acetic acid (4 vol.) and aqueous sulphuric acid (3 vol.) have been measured in order to provide information about the influence of substituents of the type p-CH₂Y in electrophilic aromatic substitution; the rates at 50° relative to that for trimethyl(phenyl)silane, with, in parentheses, the approximate derived values of σ⁺ for CH₂Y, are: (Y =) CN, 0·20 (+0·12); Br, 1·35 (–0·06); OH, 0·64 (+0·01); OMe, 1·27 (–0·05); OEt, 0·70 (0·00); CO₂H, 0·93 (–0·02); CO₂Me, 0·84 (–0·01); NMe₂H⁺, 0·0043 (+0·50); NMe₃ ⁺, 0·0042 (+0·50). The charge-transfer maxima for YCH₂Ph–tetracyano-ethylene complexes have been determined for the Y groups mentioned above and also for Y = Cl and SH; the effects of the substituents are in accord with those on the cleavage, and the frequencies of the charge-transfer maxima are linearly related to the σ_I constants for Y.