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 o f the higher efficiency of an o-carboxamido group with respect to an o -carbomethoxy group in activating the benzenethiolate-dehalogenation r eactions in methanol (k(CONH2)/k(CO2Me) 2.2-3.0) as due to an interact ion between the anionic nucleophile and the hydrogen atoms of the carb oxamido group. An inversion of the activating power of the two groups (kCONH(2)/k(CO2Me) 0.14) in the reactions with the same nucleophile ha s been observed when they are in a para-position. Moreover, for piperi dino-dehalogenation reactions in methanol k(CONH2)/k(CO2Me) ratios les s than unity (0.2-0.6) have been observed independently of the positio n (ortho or para) of the carboxamido and carbomethoxy groups with resp ect to the reaction center.