This is the wireframe of DMA (N,N-dimethylformamide). The animation starts with the structure computed by Kimball.exe. It has a pyramidal N-Atom. The successive frames show the steps of an optimization run with a RHF/6-31G(d) model chemistry using Gaussian98. The plotting software is Molden V.3.6. The main feature is the flattening of the N-atom pyramid caused by conjugation of the N-p_z orbital with the C=O p-orbital (and, perhaps, additionally some hyperconjugation with CH-bonds), not modelled with the actual Kimball.exe program. However, DMA is not flat: Electron diffraction of the gaseous molecule showed a slightly pyramidal N-atom (sum of the three CNC angles 357 deg) which is not borne out at the level of the RHF/6-31G(d) nor the B3LYP/6-31++G(d,p) model chemistries (both with angle sum 360 deg, no imaginary frequencies). Except for this feature Kimball's other structural parameters are nearly the same as those of the Gaussian result. The total energies are -245.80451(K) and -246.875037(G) hartree, respectively. Look up DMA conformer for another DMA structure, parametrized with one of the other sets of Kimball prefactors and being the lowest in energy.
Feb. 27, 2000 by ES