Studying of van der Waals Influence of Media on Absorption Stretching Vibration Frequencies in IR-spectra

M. A. Varfolomeev ; D. I. Abaidullina ; K. V. Zaitseva ; B. N. Solomonov

Učënye zapiski Kazanskogo universiteta. Seriâ Fiziko-matematičeskie nauki, Kazanskii Gosudarstvennyi Universitet. Uchenye Zapiski. Seriya Fiziko-Matematichaskie Nauki, Tome 150 (2008) no. 2, pp. 72-78

Résumé

The work regards the solvent effects on absorption stretching vibration frequencies of free molecules, complexes 1 : 1 and more complicated associated species in solution. It was shown that the solvent significantly influences band position. A model based on thermochemical solvent parameter $S_{VW}$ for solvent effect analysis was used. Frequencies of free C=O groups of acetone and free O–H groups of methanol, butanol-1 and phenol in inert (not capable of strong specific interaction) solvents were measured. Obtained values linearly depend on parameter $S_{VW}$. In these systems, solvent effect is induced by van der Waarls interactions between solute and solvent molecules. Sensitivity of stretching vibration frequencies of studied molecules to media influence is increased in series C=O (acetone) O–H (methanol) $\approx$ O–H (butanol-1) O–H (phenol). The reason of this growth is the large-scale polarization ability of O–H group. Also, the influence of non-specific solvation on stretching vibration frequencies of H-bonded O–H group of butanol-1 was studied. Frequencies of O–H group of complexes ROH\ldots B of butanol-1 with several bases B (acetone, acetonitrile, diethyl ether, dimethylsulphoxide, N,N-dimethylformamide, 3-methylpyridine, pyridine) in series of solvents were measured. Linear dependencies between obtained frequency values and solvent parameter $S_{VW}$ were observed ($\nu^{\mathrm{ROH\dots B}}=a_B \cdot S_{VW}+b_B $). For some systems, values of van der Waals interaction with solvent are similar to frequency shifts induced by hydrogen bond formation. The largest value of solvent effect is observed for complexes of butanol-1 with strong proton acceptors. From these results we can conclude that there exists a proportionality between proton acceptor ability of bases (B) and sensitivity to solvation effect. Van der Waals interaction influence on frequencies of complicated complexes with cooperative hydrogen bond was studied. In order to analyze solvent effects frequencies of H-bonded O–H groups ($\nu_b$) in ternary complexes (ROH)$_2$\ldots B of ethanol, butanol-1, butanol-2 and 2-methylpropanol-1 with pyridine and 3-methylpyridine were measured. The solvent shifts of $\nu_b$ were found to correlate with an empirical thermochemical parameter of the solvent, $S_{VW}$. In case of complicated complexes, the contribution of van der Waals interactions with solvent is also additive but it is larger than that for free molecules and binary complexes ROH\ldots B.

Détail

Keywords: solvent effect, van de Waals interactions, cooperativity, hydrogen bonding, FTIR spectroscopy, thermochemical parameter $S_{VW}$.