Nucleophilic substitution reactions of 1-halogeno-4-COR-2-nitrobenzenes and 1-halogeno-6-COR-2-nitrobenzenes with sodium benzenethiolate and piperidine. Can an ''inverted built-in solvation'' be responsible for the peculiar activation by an o-carboxamido group in SNAr reactions with an anionic nucleophile?

A kinetic study of the title reactions has allowed an interpretation of the higher efficiency of an o-carboxamido group with respect to an o-carbomethoxy group in activating the benzenethiolate-dehalogenation reactions in methanol (k(CONH2)/k(CO2Me) 2.2-3.0) as due to an interaction between the anionic nucleophile and the hydrogen atoms of the carboxamido group. An inversion of the activating power of the two groups (kCONH(2)/k(CO2Me) 0.14) in the reactions with the same nucleophile has been observed when they are in a para-position. Moreover, for piperidino-dehalogenation reactions in methanol k(CONH2)/k(CO2Me) ratios less than unity (0.2-0.6) have been observed independently of the position (ortho or para) of the carboxamido and carbomethoxy groups with respect to the reaction center.