Preferential interactions in the formamide/tetrahydrofuran/dioxane system: a study by Raman spectroscopy

Significant changes observed in the Raman spectra of formamide (FA)-tetrahydrofuran (THF)-dioxane (DX) mixtures have been interpreted in terms of preferential interactions. The Gutmann's donor (DN) and acceptor (AN) number values of these solvents give a good interpretation for the differences observed. In the ternary system, THF behaves as a stronger base than DX and the band at similar to 442 cm(-1), recently assigned to the FA-DX adduct is only observed at the highest FA concentration. Quantitative analyses performed at the C=O (FA) and C-O (THF) stretching regions show that the extent of the association for the [FA](n) adduct is significantly larger than for the FA-THF adduct. Electrostatic parameters, such as dipole moment and dielectric constant, are also regarded as a better interpretation of these associations. The good correlation between DN and electrostatic parameters indicates that the basic strength increases in the order DX < THIF < FA. Copyright (C) 2008 John Wiley & Sons, Ltd.