Substituent effects on hydrogen bonding of aromatic amide-carboxylate

Abstract

N-(p-benzoyl)-anthranilic acid (BAA) derivatives have been synthesized with different substituents (X: Br, Cl, OCH3, CH3), and their crystal structures have been analyzed in order to understand the variations in their molecular geometries with respect to the substituents by using H-1 NMR, C-13 NMR, IR and X-ray single-crystal diffraction. The carboxylic acid group forms classic O-H center dot center dot center dot O hydrogen bonded dimers in a centrosymmetric R-2(2)(8) ring motifs for BAA-Br and BAA-Cl. However, no carboxylic add group forms classic O-H center dot center dot center dot O hydrogen bonded dimers in BAA-OCH3 and BAA-CH3. The asymmetric unit consists of two crystallographically independent molecules in BAA-OCH3. DFT computations show that the interaction energies between monomer and dimer are in the range of 0.5-3.8 kcal/mol with the B3LYP/6-31 + G*, B3LYP/6-31 ++G*, B3LYP/6-31 ++G**, and B3LYP/AUG-cc-pVDZ levels of theory. The presence of different hydrogen bond patterns is also governed by the substrate. For monomeric compounds studied herein, theoretical calculations lead to two low-energy conformers; trans (a) and cis (b). Former one is more stable than latter by about 4 kcal/mol.