The SN Mechanism in aromatic compounds. 25. Substituent effects of multiple-bond nitrogen.

Abstract

The substituent effects in aromatic nucleophilic substitution of groups attached to the benzene ring by a multiple-bond nitrogen atom are considered. Attachment is para to a replaceable halogen atom, and generally as a 4-substituent to l-chloro-2-nitrobenzene. Comparisons with some other groups are shown. Reasons are given for the greater T effect of a triple than of a double bond. Hammett substituent constants (σ*) are computed. Those for the nitroso and diazonium groups .are the largest so far obtained for electrically neutral and cationic groups respectively. The activating power of four of the nitrogen groups in electrophilic as well as nucleophilic substitution is discussed briefly.