Far-infrared studies of the molecular dynamics and interactions in N-methyl formamide

Abstract

The effect of diln. in carbon tetrachloride on the far-IR spectra (5-150 cm-1) of N-Me formamide (NMF) was investigated over the whole miscibility range. The data were combined with (literature) microwave data to enable total dipole d. correlation functions to be computed. These emphasize any differences in short time dynamics which occur due to the breaking of hydrogen-bonds with diln. The data were fitted to current models for libration in a solvent "cage". The most obvious reflection of the changing intermol. potential is a large decrease in the av. intermol. torques and a corresponding change of shape of the absorption spectrum in the region of interest - esp. at lower frequencies. The rate of fluctuation of the intermol. forces is changed only marginally so the short range (repulsive) part of the potential is not severely affected. The rate of diffusion (mostly a long ranged phenomenon) is very sensitive to diln. in a non-polar solvent since co-operatively is extremely dependent on aggregate concn. The contrasting behavior of NMF and DMF (which cannot form hydrogen-bonded multimers in soln.) is emphasized and explained.