THEORETICAL-STUDY OF SIMPLE PUSH-PULL ETHYLENES IN SOLUTION

The influence of solvation on the Z-E isomerization process of three representative molecules of simple push-pull ethylenes [H2N(H)C1=C2(H)R, R = NO2, COH and CN] derived from aminoethylene was investigated by means of RHF-SCF ab initio calculations at the 3-21 + G level. Solute-solvent interactions were modelled by a cavity model. The shape of the cavity is based on electronic isodensity surfaces. By using an ellipsoidal cavity very close to the isodensity surface, the perturbation due to the solvent takes an analytical form which is incorporated into the Hartree-Fock equations and leads to efficient quantum chemical computations. The polarization of the solutes under the influence of the solvent is noticeable and was analysed in detail. Similarly, the barriers to internal rotations are substantially modified by the solvent: the barrier around the C=C double bond is appreciably decreased in the thermal mechanism whereas its lowering is less important in the anionic mechanism; in contrast, the barrier around the C-1-N bond is slightly increased. The variation of the barriers with the nature of the acceptor group is fairly well reproduced by the computations. The electronic structure of the push-pull ethylene molecules and the modifications of this structure under the influence of the solvent are analysed in detail.