Characterization of Solvent Effects on C=O Stretching Vibrations of Ketoprofen by Empirical Solvent Parameters

The solvent effects on C=O stretching vibrational frequency, ν(C=O), of ketoprofen (KETO) were studied experimentally using attenuated total reflection infrared spectroscopy (ATR-IR). The experimental ν(C=O) of KETO were correlated with empirical solvent parameters, including the Kirkwood–Bauer–Magat (KBM) equation, the acceptor numbers (ANs) of the solvents, the Swain equation, linear solvation energy relationships (LSERs), and the quadratic equation (QE). The solvent-induced ν(C=O) shifts of KETO displayed a better correlation with the LSER equation than with the KBM equation, ANs of the solvents, and the Swain equation. The linear effect of the solvent hydrogen-bond donor acidity ( A j ) on ν(C=O) of KETO was found to be highly significant, whereas the hydrogen-bond acceptor basicity ( B j ) and the interaction effect of A j and B j were not significant. It was also observed that the quadratic effects of A j and B j were slightly significant. Additionally, the linear effect of LSER parameters (π*, δ, α, and β) and the interaction effect of π*β on the ν(C=O) of KETO were highly significant.