Infrared and Raman spectroscopic studies of the association of formamide

The infrared and Raman spectra of liquid formamide and of its solutions as function of the concentration in each solvent have been investigated. As formamide is very sparingly soluble in CCl4, the infrared spectra of the amide have been studied in solvents such as chloroform, dioxane, and ethylene dichloride. The Raman spectrum of the amide has been investigated in solutions of dioxane, methanol, ethanol, and water. Significant changes have been observed both in Raman and infrared frequencies of the amide. The NH and the CO frequencies of the monomer and the trimer have been assigned and the manifestation of the trimeric state of the amide has been spectroscopically observed. The frequencies at 3364, 3280, and 3210 cm−1 have been shown to arise from the combinations of NH stretching vibrations at 3536 cm−1 with a vibration of a frequency of 86 cm−1. This low frequency line has been recorded for the first time in the Raman spectrum of the amide. The intensity of the CO band is calculated at various concentrations and the constant value of the integrated absorption intensity of the CO band below 0.009999 molar concentration is an indication of the fact that the amide does not dissociate below this concentration. The solution of formamide in dioxane—when the amide is predominantly in the monomer state—is mixed with an acceptor like phenol, and the shift in the infrared frequency of the CO band due to hydrogen bond formation is studied.