Results of Ab Initio Calculations on Formamide

Ab initio calculations on formamide, HCONH2, have been carried out for 44 nuclear configurations with a (s, p) = (11, 7) basis set for C, O, and N and a (s, p) = (5, 3) set for the hydrogens, and for three nuclear configurations with a (s, p, d) = (11, 7, 1) basis set for C, O, and N and a (s, p) = (5, 3) set for the hydrogens. Primarily, a structure from microwave work was assumed. Within the range of experimental errors of the C=O, the C–N, and the N–H distances the molecular energy was shown to pass through minima. The calculated dipole moment and the barrier to internal rotation around the C, N bond are in satisfactory agreement with experiments. Also, the changes of molecular geometry occurring if HCONH2 is twisted around its amide CN bond are consistent with qualitative expectations. The calculated barrier to NH2 inversion in HCONH2 of 30–40 cm−1 is too low by a factor of ∼ 10.

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