Acetic acid-benzaldehyde solutions: FTIR studies, DFT, isosurface, NBO and QTAIM analyses

Fourier Transform Infrared (FTIR) spectra of pure Acetic acid (AcOH), Benzaldehyde (PhCHO) and their binary solutions at various concentration have been recorded. Density functional theory (DFT) calculations using the functional B3LYP/6-311++G (d, p), isosurface, natural bond orbital analysis (NBO) and quantum theory of atoms in molecules (QTAIM) analyses have been performed on dimers of AcOH, PhCHO and their complexes in gas phase. The results of FTIR and DFT calculations have been analysed to identify the dimers present in liquid AcOH/PhCHO and the PhCHO-AcOH complexes present in the binary solutions. The liquid AcOH consists of closed nine dimers with the different interaction schemes. The frequency shift suffered by vibrational bands of AcOH or PhCHO suggest the formation of 1:1 (PhCHO:AcOH) and 1:2 complexes in the binary solutions. The 1:2 complex exist even in 1:3/3:1 binary solution and this indicates that the AcOH dimers remains stable in the diluted solutions.