Intermolecular Dynamics of Aniline in Ethyl Acetate: A Raman Spectroscopy and DFT Approach

The intermolecular interactions between aniline (PhNH₂) and ethyl acetate (EtOAc) were investigated by using Raman spectroscopy and density functional theory (DFT) calculations. Experimental Raman spectra revealed red and blue shifts in the vibrational bands of PhNH₂, indicating the presence of weak hydrogen bonding and van der Waals interactions with EtOAc. A prominent hydrogen bonding was observed between the NH₂ group of PhNH₂ and the carbonyl (C=O) group of EtOAc. DFT calculations were performed to support the experimental findings, showing strong agreement. Molecular electrostatic potential (MEP) maps highlighted the electrophilic nature of the NH₂ group and the nucleophilic character of the C=O group, corroborating the observed hydrogen bonding. Frontier molecular orbital (FMO) analysis revealed that the HOMO–LUMO energy gap of PhNH₂···(EtOAc)_n (n = 1–3) complexes decreases with increasing number of EtOAc molecules, reaching a minimum of 4.69 eV. Quantum theory of atoms in molecules (QTAIM) analysis confirmed that the complexation is primarily governed by weak hydrogen bonding and van der Waals interactions involving N-H···O=C, H-N···H–C, and C-H···O=C contacts. This study provides valuable insights into solvent effects on the molecular behavior of aniline, with implications for both fundamental research and practical applications in physics and chemistry.