Influence of dielectric environments on Raman non-coincidence effects in the CO stretching and NH2 bending modes of formamide

Abstract

This paper investigates the vibrational properties and intermolecular interactions of formamide (FA) in polar solvents with varying dielectric constants and dipole moments, including dimethyl sulfoxide (DMSO), acetonitrile (AcN), and 1,4-dioxane (DiX). Raman non-coincidence effects (NCE) in the CO stretching and NH₂ bending modes were observed to decrease monotonically in all solvents, indicating a systematic solute-solvent interaction trend. To explain such trends, experimental results were compared with the Onsager-Fröhlich dielectric continuum model, revealing strong agreement in solvents with high dielectric constants and dipole moments. Complementary DFT analyses of the Raman spectra for various FA self-associations identified a closer match with experimental results in odd-numbered molecular associations. The nature and strength of intermolecular forces in FA-solvent complexes were further investigated by topological methods (AIM, NCI, RDG), which confirmed findings from experiments. These findings advance our understanding of solute-solvent dynamics in polar environments and have broad implications for studies of intermolecular forces in chemical and biological systems.