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

Abstract 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 ∼442 cm −1 , recently assigned to the FA–DX adduct is only observed at the highest FA concentration. Quantitative analyses performed at the C (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 < THF < FA. Copyright © 2008 John Wiley & Sons, Ltd.

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