A theoretical study on dimerization and dissociation of acetic acid in ethanol solvent

Electronic structure calculations are applied on acetic acid monomers, dimers and clusters in water and ethanol solvent. Acetic acid is normally existed as dimeric structure in gas, vapor and liquid phase. It is predicted that sufficient ethanol molecules can dissociate this dimeric structure, while stable clusters can be formed by acetic acid units and ethanol units. To investigate this process, optimized structures, geometry parameters, interaction energy values and simulated Raman spectra of acetic acid dimers and clusters are discussed. Geometry parameters indicates that at least three ethanol molecules can break the dimeric structures, while just two H2O molecules are needed to dissociate acetic acid dimer. Interaction energy parameters justify the minimum number of solvent molecules to break dimeric structures further. Energy decomposition analysis of interaction suggests that hydrogen-bond interaction plays a central role in interaction and acetic acid clusters with ethanol units have higher value of electrostatic energy than that of hydrated clusters, which causes that more ethanol molecules are needed to break acetic acid dimer than water molecules. Reduced density gradient function analysis investigates the position and strength of H-bond interaction. The red shifts of the O-H peak position of theoretical spectra for acetic acid clusters imply the weakening of O-H stretching and the strengthen of H-bond interaction while clusters' size enlarging. Experimental Raman spectra justify the result of theoretical spectra.