Raman Spectra and Quantum-Chemical Computational Analysis of Intermolecular Interactions in Ortho-Xylene and Its Solutions with Chloroform

We report a study of the vibrational spectra of ortho-xylene in pure form and in solutions with chloroform at room temperature and atmospheric pressure. Raman spectra of binary mixtures of ortho-xylene and chloroform with concentrations of 0.9, 0.7, 0.5, 0.3 and 0.1 mole fractions are analyzed. It is found that the 733 cm‒1 band of symmetrical stretching vibrations of CH3 groups in pure ortho-xylene shifts toward lower frequencies (728 cm‒1) when chloroform is added to the solution. The main reason for the shift is the interaction of the π-electrons of the aromatic ring with the hydrogen of the CH-group of chloroform (CH…π interaction), leading to a decrease in the vibration frequency. Furthermore, a noticeable shift of the band associated with C–H stretching vibrations is observed in the region of 3011 cm–1, which also indicates a change in the nature of the intermolecular interactions between the components of the solution. Furthermore, the spectrum reveals an additional shift in the region of 3044 cm–1, confirming the influence of solvation effects: the C–H dipole of chloroform interacts with the π-electrons of ortho-xylene, changing the C–H bond length and, consequently, shifting the vibrational frequency toward higher frequencies. The exchange of charges between atoms during the formation of the complex is analyzed. The structural parameters of molecules, molecular electrostatic potential (MEP), and Mulliken distribution of atomic charges are studied using the density functional theory (DFT) method.