Intramolecular hydrogen bond-driven conformational preferences in pyridine-containing dibenzamide and dicarboxamide derivatives: evidence from NMR and DFT-based computation

Abstract

The hydrogen bond (HB) plays a pivotal role in controlling numerous chemical and biological processes. The impact of inter- or intramolecular interactions is well established in supramolecular chemistry as well as in the structural organization of proteins, peptides, foldamers, etc. Fluorine involved in hydrogen bonding is particularly important in the pharmaceutical industry due to its influence on molecular stability and biological activity. Considering this, a series of pyridine-containing benzamide and carboxamide derivatives with ortho-substituted phenyl rings were synthesized to study the influence of intramolecular hydrogen bonding on molecular conformation. The existence of weak molecular interactions and their control on molecular conformations are investigated through experimental NMR techniques and density functional theory (DFT)-based theoretical calculations. The detection of HB-mediated 1hJFH and 2hJFN couplings, monitoring the effect of dilution, temperature, and polarity variation on the chemical shifts of HB-involved labile –NH protons, confirmed the existence of intramolecular HBs in the investigated molecules. The experimental findings are further validated by DFT calculations, Boltzmann population distribution and relaxed potential energy surface (PES) scans, Quantum Theory of Atoms in Molecules (QTAIM), non-covalent interaction (NCI), and natural bond orbital (NBO) analyses.