Inversion, rotation, charge distribution, and resonance in nitramide

Molecular orbital calculations were performed for nitramide in several geometries. At 3-21G, nitramide is predicted erroneously to be planar; bigger basis sets including polarization functions correct this, yielding an inversion barrier of about 1 kcal/mol at HF/6-31G*//HF/6-31G*. Consideration of electron correlation effects and zero-point energies yields an inversion barrier of 2.2 kcal/mol at RMP2/6-31G*//RMP2/6-31G*, in good agreement with experiment. The rotational barrier is calculated to be about 10-12 kcal, with HF calculations giving a larger barrier than MP2. In addition, charge distributions were obtained and the thermodynamic stabilization due to resonance was estimated. Neither of these quantities suggested an important role for resonance.