Intermolecular interactions in water and ethanol solution of ethyl acetate: Raman, DFT, MEP, FMO, AIM, NCI-RDG, ELF, and LOL analyses

The intermolecular interactions of ethyl acetate (EtOAc)-water (H₂O)/ethanol (EtOH) mixtures were investigated using a combination of Raman spectroscopy and quantum chemical calculations. The computational approach was used to analyze the structure of hydrogen-bonded complexes of ethyl acetate with water/ethanol molecules, based on density functional theory (DFT). The calculated frequencies closely matched the experimental Raman values, with differences being under 4%. Experimental data show that when the concentrations of ethyl acetate in the ethyl acetate/water/ethanol solutions were reduced, almost all Raman spectral bands are blue-shifted. The AIM analysis reveals that all the given complexes possess a positive energy density, indicating that the molecules interact electrostatically. The energy and bond length indicate that the methyl group forms relatively weak hydrogen bonds. Analysis indicates that EtOAc forms weak H-bonding C = O∙∙∙H and C-H∙∙∙O, which are recognized as van der Waals interactions. As the amount of ethyl acetate decreases in the complex, the interaction forces also decrease. This could also explain why the bands are blue-shifted. It was discovered that the title complexes’ hydrogen bond energy decreased exponentially as bond length increased.

The geometries of the molecular complexes were optimized using the Gaussian 09W program and the B3LYP/6–311 +  + G(d,p) set of functions. The potential energy distribution (PED) analysis was performed using VEDA 4.0 software. Raman spectra were drawn using the Origin 8.5 software. The Multiwfn 3.8 software was used to calculate topological parameters of electron density in molecular systems. GaussView 6.0 and Visual Molecular Dynamics (VMD) 1.9.3 tools were used to visualize all computational results.