
%0 Journal Article
%A Radom, L 
%A Riggs, NV 
%T Saddle-point geometries and barriers to internal rotation of formamide : an <I>ab initio</I> study
%J Australian Journal of Chemistry
%D 1980/02/01
%V 33
%N 2
%P 249-255
%K 
%R https://doi.org/10.1071/CH9800249
%U https://www.publish.csiro.au/paper/CH9800249 
%X By use of a direct transition-state program and the STO-3G minimal basis set, two saddle-points are detected on the energy surface for internal motion of formamide. These correspond mainly to rotation about the C-N bond along with some lengthening of this bond and increased pyramidal distortion at nitrogen as compared with that in the ground state. The STO-3G estimates of the barrier height (34-39 kJ mol-1) are in very poor agreement with experimental values (70-90 kJ mol-1), but 4- 31G energy evaluations for the STO-3G-optimized structures give much better estimates (62-80 kJ mol-1). Contrary to a previous report, use of the 4-31G extended basis set for geometry optimization suggests that only the lower-energy member (NH2 cis to CO) of the above pair is a true transition state for internal motion of formamide; its energy relative to that of the 4-31G-optimized ground state (planar) is 83.5 kJ mol-1, very close to the midpoint of the experimental range. The transition state appears to lie in a region of the 4-31G energy surface that is relatively flat with respect to pyramidal distortion at nitrogen; constraining the amino group to planarity raises the calculated energy by only 6.5kJmol-1. 
