Results of Ab Initio Calculations on Formamide

Abstract

Ab initio calculations on formamide, HCONH₂, have been carried out for 44 nuclear configurations with a $\text{(s, p)\hspace{0.17em}=\hspace{0.17em}(11, 7)}$ basis set for C, O, and N and a $\text{(s, p)\hspace{0.17em}=\hspace{0.17em}(5, 3)}$ set for the hydrogens, and for three nuclear configurations with a $\text{(s, p, d)\hspace{0.17em}=\hspace{0.17em}(11, 7, 1)}$ basis set for C, O, and N and a $\text{(s, p)\hspace{0.17em}=\hspace{0.17em}(5, 3)}$ 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.