Substituent effects in the electrophilic substitution of deactivated systems. Part II. The Mills–Nixon effect and the nitration of strained 1,2,3,4-tetrahydroquinolinium ions

Abstract

Second-order rate coefficients have been measured for the nitration in 82% aqueous sulphuric acid of a series of strained 2-alkyl-1-methyl- and 2-alkyl-1,4-dimethyl-tetrahydroquinolines. Product analysis reveals the surprising absence of 5-nitro-compounds and this, together with variations in the ratios of 6- to 7-nitrated products, is consistent with the explanation of the Mills–Nixon effect in terms of strain in bonds common to fused rings. Varying initial state strain does not appreciably affect the overall rate of nitration.