The structure of liquid formamide studied by means of X-ray diffraction and NMR at high temperatures and high pressures

Abstract

Abstract The structure of liquid formamide has been investigated by means of X-ray diffraction and NMR at high temperatures and high pressures (HTHP). The temperatures were fixed at 298 K and 373 K, and the pressures employed were 0.1, 20, and 40 MPa for the X-ray diffraction studies, while the NMR measurements were carried out over the temperature range from 300 K to 395 K at 0.1 MPa and over the pressure range from 0.1 to 200 MPa at 298 K. Formamide has a network structure consisting of a mixed ring and head-and-tail-type linear structures through N-H⋯O hydrogen bonds at 298 K and 0.1 MPa, and the ring structure, which has weaker hydrogen bonds than the linear structure, is broken with increasing temperature to change to the linear-type structure. On the other hand, the linear structure changes to the ring structure, having a more compact molecular arrangement than the linear one, with the increase in pressure.