Complex formation of HCONH 2 in CH 3OH environment and investigation of linewidth changes of ν(C [dbnd]O) stretching and NH 2 bending modes

Abstract

The isotropic part of the Raman bands corresponding to NH 2 bending and ν(C O) stretching modes of formamide (HCONH 2) at ∼1593 and 1668 cm −1, respectively, in neat HCONH 2 as well as in binary mixtures with methanol (CH 3OH) were reinvestigated. Variations of their linewidths exclusively with mole fractions of HCONH 2, in the range C = 0.1–0.9 were studied. The linewidth variation of the NH 2 bending mode shows a departure from the trend expected on the basis of concentration fluctuation model and this has been explained using a recently suggested empirical model by invoking the concept of microviscosities of the solute, HCONH 2 and the solvent, CH 3OH. The other peak at ∼1668 cm −1 shows a peculiar variation of the linewidth with concentration having two minima at C = 0.8 and 0.4, which have been explained in terms of formation of hydrogen bonded complexes, NH 2HCO⋯HOCH 3, and NH 2HCO⋯(HOCH 3) 2 and the two phenomena, namely motional narrowing and diffusion dynamics being simultaneously operative. The equilibrium constants have been evaluated from the spectral data and their variation with total molar concentration has been presented.