Zwitterion formation and subsequent carboxylate–pyridinium NH synthon generation through isomerization of 2-anilinonicotinic acid?

CrystEngComm Pub Date: 2018-09-12 DOI: 10.1039/C8CE01255E

Abstract

Through structural modification of 2-anilinonicotinic acid by isomerization, the ΔpKa between the carboxylic acid and pyridinium NH increased dramatically over the threshold to form zwitterions in the newly designed 4-anilinonicotinic acids. This in turn led to the formation of a hydrogen bond between carboxylate and pyridinium NH, and the absence of two commonly observed synthons, i.e., the acid–acid homosynthon and acid–pyridine heterosynthon. The new synthon has a stronger hydrogen bond than the acid–acid homosynthon and the acid–pyridine heterosynthon, as suggested by theoretical calculations. This, together with the much larger ΔpKa, explains its formation.

Graphical abstract: Zwitterion formation and subsequent carboxylate–pyridinium NH synthon generation through isomerization of 2-anilinonicotinic acid
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