Influence des solvants sur la transition n → π * des cétones saturées

Abstract

It has been found that the positions of absorption maxima (ν s ) of the n → π * transition in the 33000–38000 cm −1 region for ketones in various solvents are also dependent on the structure of the ketone. The authors found that M acR ae's formula cannot be applied directly to the experimental observations without introducing serious restrictions as to generality. Their study based on the specific properties of a ketone series for a solvent coupled with a linear free energy postulate permits the development of an excellent description of these absorption maxima in terms of the nature of the solvent and of the structure of the ketone. This work has been carried out for eight aliphatic ketones (Me CO Me, Me CO Pr, Me CO i Bu, Pr CO Pr, Me CO neoPe, Pr CO neoPe, tBu CO neoPe and tBu CO tBu) in fourteen solvents (hexane, benzene, cyclohexane, isooctane, dioxane, diethyl ether, tetrahydrofuran, dimethyl-formamide, acetonitrile, chloroform, t-butyl alcohol, ethanol, methanol and water). The correlations ν s = f(ν H ), which relate the behavior of the ketone series in various solvents to their comportment in hexane, permit a meaningful generalized description of the solute-solvent system. All of the solvents, including water, may be described by a linear expression of the form ν s = A s ν H + B s . Numerical values of A s and B s have been calculated for the fourteen solvents investigated. A more refined treatment makes it possible to isolate the influence of the solvent on the n → π * transition of this series of ketones by means of the following equation ν s - ν H = F(ν H - ν I ) ν I = 33370 cm −1 which is applicable to all of the cases studied except water. The values of the parameter F of all the solvents are compared with the known G and Z spectroscopic functions. Furthermore this expression points to the existence of ketones for which ν s will be constant in different solvents and suggests therefore a certain steric inhibition of solvation.