Manifestation of intermolecular hydrogen bonding in heterocyclic compounds of pyrrol derivatives according to infrared spectroscopy and quantum chemical calculations

The formation of H-complexes in solutions of nitrogen-containing heterocyclic compounds of the pyrrole group (pyrrole, indole, carbazole) with a proton-acceptor solvent (acetone) has been studied. Based on the results of IR spectroscopic studies and quantum chemical calculations, it has been shown that intermolecular hydrogen bonds of the N-H O = C type are formed between carbazole and acetone molecules, which leads to a shift in the vibration frequency of N-H groups of free molecules towards low frequencies with simultaneous broadening and strengthening of this band. The magnitude of the change in the spectroscopic and energy parameters of the H-complexes depends on the type of structural elements introduced into the pyrrole cycle. It has been found that the donor capacity of the studied compounds, which has been determined by their equilibrium electronic structure, is low and increases upon going from pyrrole to its derivatives. (author)