Substituent effects of positive poles in aromatic substitution. Part VII. Effect of nitrogen and arsenic poles on the orientation and rate of bromination by hypobromous acid

Abstract

The bromination of the phenyltrimethylammonium ion by hypobromous acid in aqueous sulphuric acid gives 66 ± 1%meta-substitution, 33 ± 1%para-substitution, and less than 2%ortho-substitution. Under the same conditions, bromination of the phenyltrimethylarsonium ion gives 90 ± 2%meta-substitution, 10 ± 2%ortho-substitution, and less than 3%para-substitution. The rates of bromination of these ions and of a number of other benzene derivatives with positively charged substituents have been measured. The results are compared with those obtained in nitration, and for the nitrogen poles are explained in terms of the electrostatic interaction between the pole and the charge on the aromatic ring or on the electrophile in the transition state. The substituent effects of other poles are shown to be consistent with the superposition of conjugative effects on this electrostatic interaction.