In order to explore polymers with precisly defined molecular architecture and to better explore structure-propertie relationships, spectroscopic results are combined with theoretical ones in order to describe the copolymerization mechanism of poly(vinyl)carbazole and 3-methylthiophene. The umpaired electron spin densities of radical cations are determined at the differents steps during the oligomerization using DFT calculations. The purpose is to propose an oligomer model that reflect properties of the copolymer (PVKMeT).

It has been demonstrated that five-membered aromatic heterocycles are capable of undergoing normal electron demand Diels-Alder reactions with a variety of dienes. The global electrophilicity index of these dienophiles have been studied in order to predict the relative reactivity towards cycloaddition reactions. Influence of the type of substitution have also been discussed and compared with experimental results.

A comprehensive B3LYP/6-31+G* study of the influence of BF3 on the [4 + 2] cycloaddition of vinylketene with formaldimine was conducted. For this purpose, the complete pathway was determined and changes in different magnetic properties (magnetic susceptibility, χ, magnetic susceptibility anisotropy, χanis, and the nucleus-independent chemical shifts, NICS) were monitored along the reaction profile with a view to estimating the aromatization associated to the process. We have also applied the ACID (anisotropy of the current-induced density) method with the same intention.

A theoretical study of the "walk" rearrangement in bicyclo[2.1.0]pentene and perfluorotetramethyl (Dewar thiophene) exo-S-oxide has been carried out. In order to analyze the pericyclic character of these two reactions, some magnetic properties (NICS and ACID) have been calculated in the reactant/product and in the transition state of each reaction. Despite the differences between them, the results for both reactions show an enhancement of aromaticity in the transition state, which is consistent with a pericyclic behavior. NBO calculations show that the small activation energy for the second reaction can be interpreted in terms of a strongly stabilization of the transition state by the exo-oxide substituent. No evidence of any pseudopericyclic character has been found. Although the walk rearrangement in erfluorotetramethyl (Dewar thiophene) exo-S-oxide has special characteristics, the process of [1,3]-sigmatropic shift remains with a fundamental role in its mechanism. So, the mechanism proposed by Lemal et al, should be revised.

Electrocyclization reactions of 1,2-divinylbenzene and several related molecules were studied by performing density functional theory (DFT) calculations together with the 6-31+G* basis set. Reactants, products, and transition states for each reaction were localized and the IRC connecting reactants and products was also obtained. Magnetic properties were evaluated along the reaction path to elucidate the characteristics of the reactions studied with respect to their aromaticity and pericyclic character. Though reactions B and C seem to be borderline cases between pericyclic andpseudopericyclic behaviour, the analysis of different magnetic properties allow us to conclude that all reactions studied are pericyclic.

Density functional theory computations elucidated the ring opening of benzoannulated derivatives of bicycle[4.1.0]hept-7-ylidene (6). The B3LYP geometry optimizations and single-point energies employed a 6-31G (d) basis set. The ring opening barrier leading to cycloallenes, 11 and 15 is predicted to be 11.11 and 9.52 kcal/mol, respectively, which are lower than that for the ring opening of cyclopropylidene 6 (15.1 kcal/mol). This explains that 11 and 15 could be generated if Doering-Moore-Skattebol reaction is carried out for this purpose.