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A computational study of the chemical kinetics and thermodynamics study of the S N Ar between 3,5-dinitroethoxypyridine  1a  and 3,5-dinitromethoxypyridine  1b  with piperidine  2  in the gas phase is reported using hybrid density functional theory method B3PW91 and 6–31G(d,p) basis set. The reaction was modeled via both the catalyzed and base-catalyzed pathways which proceeded with the initial attack of the nucleophile  2  on the substrates  1  to yield the Meisenheimer complex intermediate that is stabilized with hydrogen bonding. Calculations show that the reaction goes  via  the formation and decomposition of a Meisenheimer complex, which was observed to be stabilized by hydrogen bonding. Along the uncatalyzed pathway, the decomposition of the Meisenheimer complex was the slow step and requires about 28 kcal/mol. This barrier was reduced to about 14.8 kcal/mol with the intervention of the base catalyst, thus making the formation of the Meisenheimer complex rate determining. All reactions were calculated to be exothermic, about −6.5 kcal/mol and −0.6 kcal/mol, respectively, for the reaction of  1a  and  1b  with  2 .

A computational study of the S N Ar reaction of 2-ethoxy-3,5-dinitropyridine and 2-methoxy-3,5-dinitropyridine with piperidine