Enforcing Molecule’s π-Conjugation and Consequent Formation of the Acid−Acid Homosynthon over the Acid−Pyridine Heterosynthon in 2-Anilinonicotinic Acids

Two different synthons, acid−acid and acid−pyridine, are present in the crystal structures of 2-(phenylamino)nicotinic acid. The intermolecular hydrogen-bonding motifs are determined by molecular conformation and conformational energy. By covalently linking electron-withdrawing groups to the phenyl ring, it is possible to strengthen the molecule’s global π-conjugation and thereby lead to only the acid−acid homosynthon in crystal packing and prohibit the competing acid−pyridine heterosynthon.