Structure of formamide and its force constants

V. Summary

A new procedure has been adopted in subjecting formamide—a molecule which has no symmetry—to normal co-ordinate treatment by the Wilson’s F-G matrix method. The molecule is split into two parts for the purposes of calculation. One part is

and the other is

where R is the CHO group. Both the parts have C-N bond in common. Assuming the part one to be planar and the part two to be pryamidal as suggested by Costain and Dowling, the normal co-ordinate treatment of both the parts has been carried out and the fundamental frequencies calculated. The close agreement between the observed and the calculated values confirms the non-planar structure of formamide. Among all the fundamental frequencies, the frequency due to C-N stretch alone appears to be mass sensitive. On the basis of all these considerations some of the frequencies have been assigned to the wagging and twisting modes, which are different from those that are assigned by Evans.