Ingegerd Wennerbeck

Studies of polarized ethylenes.: PART VII.1 experimental and theoretical dipole moments and electronic structures by CNDO/2 calculations

Abstract The dipole moments of a number of representative “push-pull” ethylenes have been calculated by the CNDO/2 method, and a comparison is made with experimental dipole moments, which are in general surprisingly well reproduced. An analysis of the calculated charge distributions shows that the π-electron displacements are in agreement with qualitative expectations, but no back-polarization of the σ-electrons can be observed. Instead, the distribution of the σ-electrons seems to be governed by atom electronegativities. The experimental dipole moments of some more or less flexible analogues are discussed in relation to conformations and expected charge distributions.

CNDO/2 calculations of rotational barriers in N.N-dimethylamino-azines: Lineshape study of the barrier in 3-dimethylamino-1,2,4-triazine

Abstract 3-Dimethylamino-1,2,4-triazine has been prepared and the hindered rotation around the exocyclic C-N bond has been studied by a complete lineshape method. CNDO/2 calculations on dimethylamino derivatives of pyridine, pyrimidine, 1,2,4-triazine and 1,3,5-triazine have been performed, and it is found that the calculations satisfactorily reproduce the experimental data. The barrier heights are also discussed in terms of total and π-charge densities obtained from CNDO/2 calculations.

Conformational study of twisted ethylenes by nuclear magnetic resonance spectroscopy

The temperature-dependent n.m.r. spectra of 2-(diacylmethylene)-1,3-dialkylimidazolidines show that the molecules are twisted around the carbon–carbon double bonds and that the planar states represent energy maxima; in the 1,3-dibenzyl derivatives the benzylic protons are non-equivalent at ambient temperature and hindered rotation of the acyl groups is also observed.