Acid–base interactions between formamide and tetrahydrofuran molecules: Raman investigation of speciation in a binary system of biological interest

Raman spectra of formamide (FA) and tetrahydrofuran (THF) mixtures at different compositions were obtained. The appearance of new bands at 897 and 1612 cm⁻¹, whose intensities show large dependence on the FA concentration, are assigned to an FA–THF adduct. This assignment is supported by the Lewis acid–base theory, where the two H‐bond donor sites of FA and the strong donor character of THF became the environment propitious for the donor‐acceptor reaction. Quantitative measurements performed in the band envelope at ∼915 cm⁻¹ allowed to determine the stoichiometry of the Lewis acid–base adduct. The experimental evidence of the 2:1 FA–THF adduct is presented for the first time using Raman spectroscopy and our results show an excellent agreement with similar systems. The present work also shows hydrogen interactions which can be involved in systems containing peptide groups and constituents of nucleic acids. Copyright © 2008 John Wiley & Sons, Ltd.