An investigation of the transmission of electronic effects in a series of 5- and 6-substituted benzazoles by the methods of basic deuterium exchange and nmr spectroscopy

The kinetics of deuterium exchange at the methyl groups in 5- and 6-substituted 2-methylbenzothiazoles, 6-substituted 2-methylbenzoxazoles, and 5-substituted 1,2-dimethylbenzimidazoles have been studied. A quantitative estimate of the influence of the substituents on the free energy of activation of deuterium exchange and on the chemical shifts in the 1H, 13C, and 19F NMR spectra of the benzazoles investigated and of the substituted quinolines and napthalenes used as standard systems has been made with the aid of correlation analysis. It has been shown that the decrease in the transmission capacity of the benzazole nucleus in the transition state of the reaction as compared with the initial state is due to the influence of cross-conjugation effects disturbing the additive nature of the electronic interactions. The question of the probable structure of the transition state of the reaction is discussed