Michel Rajzmann

Calculs «a priori» de constantes physiques moléculaires à partir de méthodes SCF sémi-empiriques. I. Influence des orbitales d dans la série des chloréthylènes

CNDO/S method has been employed to evaluate different physical observables in chloroethylenic compounds: dipolar moments, transition energies in u.v. region and C-13 N.M.R. chemical shifts.Introduction of d orbitals in the basis improve the computed values, and the CNDO/S method appears to be better than CNDO/2 to evaluate these physical constants.

Localized virtual and occupied molecular orbitals

This report describes the generation of localized from canonical molecular orbitals such that the method (1) be consistently applicable to occupied bond, lone pair and unoccupied orbitals and (2) permit symmetry related orbitals in molecules of two-fold or higher symmetry. Minimization of populations completely external to each local pair region effectively meets these criteria. Finally, conventional strategy for finding the global extremization point is costly in time and memory to implement; a much more efficient numerical search procedure for the global extremum is described. Results for ethylene, butadiene and benzene are presented to clarify the difficulties and their resolution.

Moments dipolaires et conformations de l'hexaméthyl-phosphotriamide (HMPT) et des dérivés aziridinylés correspondants

Abstract Some physical properties (density, refractive index, dielectric constant, dipole moment) have been determined for the phosphoramides Variations of dielectric constant and dipole moment as a function of the structure show a minimum for n = 2. In order to explain this minimum, the dipole moments are evaluated for various conformations, using both a rigid dipoles summation and quantum calculations (CNDO/2). The values adopted for the bond angles and for the interatomic distances are discussed. The conformation in which the three nitrogen lone pairs are essentially parallel to the PO axis (one in the same direction, two in the opposite direction) seems to be applicable to all the phosphoramides studied. In the case of HMPT ( n = 0), however, the arrangement in which the nitrogen lone pair is parallel to the PO axis in the opposite direction, and the two others in a plane perpendicular to PO, seems to be more reasonable. These structures are compared with those for some related compounds. Relationships between the basicity (deduced from proton NMR chemical shifts of hcci 3 ) and the orientation of dipole moment are discussed.

A theoretical and comparative CNDO study of chlorophylls a and b and their beryllium homologs.

Abstract CNDO/II calculations of chlorophylls a and b and their beryllium homologs show that the 3d atomic orbitals of the metal atoms contribute significantly to the σ and π bonding energies. In both chlorophylls a and b replacement of magnesium by beryllium stabilizes the total molecular energy by 40 kcal/mol.