Self-association of formamide in carbon tetrachloride solutions: An experimental and quantum chemistry vibrational and thermodynamic study

Dilute solutions of formamide in carbon tetrachloride were studied by infrared spectroscopy in order to detect, characterize, and measure the bands of the formamide dimers. The structural and spectroscopic properties of these dimers, open or cyclic, were calculated using DFT procedures, with the B3LYP functional and 6-31G(d,p) or 6-31++G(d.p) basis sets, allowing proper assignments for the mentioned bands. Although a planar structure was predicted by the calculations for the monomer and cyclic dimer of formamide, in agreement with other authors, a nonplanar structure was found for the donor formamide molecule in the open dimer. Measurements made with solutions of different concentrations and at different temperatures allowed an estimation of the equilibrium constants between formamide and its dimers and of the corresponding dimerization enthalpies. Acceptable agreement was found between these experimental enthalpies and theoretical values after taking into account the solvation effects.