Michel Pesquer

A theoretical study of aniline and some derivatives in their ground states

Abstract Geometries and energies of some para-substituted N , N -dimethylaniline derivatives have been calculated using AM1 and ab initio methods for planar and various pyramidal structures with full geometry optimization. The calculated geometry characteristics for aniline show the ability of some theoretical methods to reproduce accurately the experimental data. The influence and interdependence of rotation and inversion angles around C-NX 2 of the amino group are discussed in relation to the nature of the substituents on dimethylaniline. Qualitative and quantitative rules are formulated for the structural properties of these compounds.

Structural and energy properties study using the AM1 calculations of aza-azulenes in their ground state

Abstract AM1 calculations with complete optimization have been carried out on the azulene molecule and its derivatives such as 1-aza-azulene and 1,3-diaza-azulene. We show that AM1 is an appropriate method for predicting the structure and energy properties of azulene. Experimental values are found with good accuracy and computer results are analogous to those obtained by sophisticated methods such as the ab initio method (6-31G ∗ ). We describe a complete theoretical study of the structural and energy properties of 1-aza-azulene and 1,3-diaza-azulene in their ground states using the same method with full geometry optimization. From the theoretical finding, the most stable conformations are proposed. Otherwise, these geometrical conformations are preserved in order to determine some spectroscopic values of these compounds using the CNDO/M method. Our results are in qualitative agreement with the experimental data.

Extended Huckel calculations of carbon chemical shifts with the aid of Gauge-Invariant Atomic Orbitals

Abstract 13 C shielding constants have been calculated by means of the Extended Huckel Theory using Gauge-Invariant Atomic Orbitals (GIAO) and including a large number of terms arising from the Hamiltonian and orbital expansions. The results indicate that the method can account for the general trends of 13 C chemical shifts. It is shown that an approximation in which the paramagnetic contribution is calculated, by retaining a determined type of two-centre terms, gives a correct description of the observed effects.

Extended London theory of diamagnetism. I. General theory and saturated hydrocarbons

In this paper a method is proposed to calculate diamagnetic susceptibilities of organic compounds. This method uses the extended Huckel formalism generalized to include the perturbation due to a magnetic field H. Parameters are varied to obtain agreement with experimental results. The diamagnetic properties of the alkanes are examined and all the terms contributing to the susceptibility are analyzed. The importance of a coupling term between matrix elements of first order in H and London terms is shown. Some results are discussed, particular to methane and the cycloalkanes.

Extended Hückel calculation of proton chemical shifts with the aid of gauge invariant atomic orbitals. Application to hydrocarbons

A theory of proton magnetic shielding constants is developed within the Extended Huckel formalism using gauge invariant atomic orbitals. The major part of the terms arising from the hamiltonian and orbitals expansions is evaluated. The method is applicable to relatively large molecules and the calculated chemical shifts agree to generally better than 1 p.p.m. with the experimental values. The results for alkanes, ethylenic compounds and benzene are analysed.

Extended London theory of diamagnetism Unsaturated hydrocarbons

The extended London theory of diamagnetism is applied to the calculation of the susceptibilities and the anisotropies of unsaturated hydrocarbons. The agreement with experimental results is good.

The use of Fraga's potential with AM1 atomic point charges in the evaluation of spectral shifts: application to TICT molecules

Fraga potential calculations with atomic point charges and geometrical parameters calculated from AM1 calculations have been used to calculate spectral shifts upon electronic excitation in twisted intramolecular charge transfer (TICT) systems due to intermolecular interactions. Changes of atomic polarizabilities have also been taken into account. Present calculations deal with absorption transitions of the p‐N,N‐dimethylaminobenzonitrile (DMABN) surrounded by methane, water, acetone, or acetonitrile solvent molecules. The methodology permits us to evaluate the influence of the solvent molecule on DMABN dimethylamino motions and to find the most stable conformation of a cluster configuration which can lead to a blue or red shift. The results have been compared with the experimental work of Warren et al.7 and confirm their analysis.

Extended London theory of diamagnetism Analysis of theoretical magnetic susceptibilities

Magnetic susceptibilities and anisotropies of unsaturated hydrocarbons are analysed in connection with the extended London theory framework. Five principal contributions are discussed and their additive character is examined. Their relative importance characterizes the structural particularities of the different studied compounds. For aromatic molecules a coupling term, of the same order of magnitude as the contribution from π electrons ring currents, represents 50 per cent of the anisotropy. The diamagnetism of fulvene, pentalene, cyclopentadiene, allene, acetylenic and ethylenic compounds is examined in detail. An appendix discusses contributions to the anisotropy of linear alkanes.