Frieder Birnstock

Quantum chemical calculations for the determination of the molecular structure of conjugated compounds: Part XIV. On the conformational structure of α-diimine ligands

Abstract The conformational structure of some typical α-diimine ligands (2,2′-bipyridyl, glyoxaldiimine, glyoxal-N,N′-dimethyldiimine) is examined using the NDDO method. An analysis of the potential energy curves indicates the influence of specific lone-pair effects on the molecular structure. Based on a continuum model, changes of the molecular arrangement caused by solvent effects are estimated.

Quantum chemical calculations for the determination of the molecular structure of conjugated compounds: Part XIII. On the conformational structure of rans-benzylideneaniline in the gas phase and in solution

Abstract Contrary to the results of other semi-empirical all-valence electron methods, the main features concerning the conformation of trans -benzylideneaniline are correctly accounted for using the NDDO method. Based on a modified continuum model the influence of solvents on the molecular structure was estimated.

The electrostatical molecular potential — A tool for the prediction of electrostatic molecular interaction properties

Starting from the molecular potential we get, by using elementary electrostatics, information about energetically favoured regions for interaction with ions and dipoles around H2O and H2CO. The molecule-dipole interaction is represented by the electric field patterns.

Influence of solvents on the properties of chemical compounds: I. Determination of the conformational structure of biphenyl, butadiene, benzaldehyde, propionaldehyde, furfural and formamide by means of a continuum model

Based on Sinanoğlus solvent theory in connection with a method for the calculation of the molecular volume given by Beveridge a modified continuum model is suggested. The model is tested by the determination of the conformational structure of the title compounds. The predictions obtained by this model are in good agreement with the experimentally determined data.

Calculation of second-order properties with improved virtual orbitals

Abstract 13 CH nuclear spin coupling and 13 C shielding constants of CH 4 , C 2 H 6 , C 2 H 4 , C 2 H 2 are calculated by means of the second-order perturbation theory and MO LCAO wavefunctions. The aim of this paper is to test the ability of the recently proposed virtual orbitals to accelerte the convergence of the sum over states, compared to the calculation with canonical MOs. The 13 CH nuclear spin coupling constants show a significant improvement, the changes of the 13 C shielding are insignificant.

Calculations with an extended CNDO APSG procedure

Abstract An extension of the CNDO APSG procedure is given by adding one-electron transfer terms and doubly excited APSG wavefunctions, following Kapuys formalism. This configuration interaction is treated perturbationally using a Rayleigh-Schrodinger expansion. Preliminary test calculations including one-electron transfer to third order of perturbation energy are performed and compared with PCILO results.

Simplified ab initio calculations on small molecules with an extended balanced approximate MO formalism

Abstract Based on a test of different known simplified ab initio methods an approximate LCAO MO formalism is proposed which gives reasonable results in a minimal STO basis in comparison with ab initio calculations.