Polar effect

Abstract: Several 1,8-diarylnaphthalenes have been prepared, and the barrier to rotation around the arylhaphthalene bond has been measured. In these molecules steric congestion forces the aryls in a parallel stacked geometry. The barriers to rotation were used to evaluate the strength and to investigate the nature of the interaction between the arenes. The variance of the AG+ for the rotation upon arene substitution with electron donating or electron withdrawing groups indicates that polarh electrostatic effects dominate over charge-transfer effects in determining the arene/arene interaction.

Abstract: The traditional homogeneous access to aromatic amine derivatives is a nucleophilic aromatic substitution of the corresponding aryl halides. The halogen atom is usually relatively inert to amination reaction unless it is activated by the presence of electron withdrawing groups. Consequently, there has been particular emphasis over the past decade on the synthesis of metal complexes that are active catalysts for the preparation of aromatic amines. This tutorial review focuses on the use of metal-based complexes for the direct amination of aryl halides with ammonia.

Abstract: The Diels–Alder reaction leads to a mixture of two diastereomers, one called endo and the other one exo. The cyclo-reversion temperature of the first one is lower than the exo adduct and the ratio between endo and exo adducts varies according to the substituents of the Diels–Alder partners and experimental parameters. Therefore, the influence of some reaction parameters such as the substituents of furan and maleimide derivatives, the reaction temperature and the presence of a nucleophile on the endo/exo Diels–Alder ratio and/or the retro-Diels–Alder reaction have been studied. For instance, furan and maleimide derivatives with electron withdrawing substituents induced the creation of the endo adduct preferentially. Also the presence of a far electron withdrawing substituent on furan and/or an electron attracting mesomeric substituent on maleimide resulted in a faster reversibility of the endo adduct. Finally, a high temperature and the presence of a nucleophile (thiol) also induced faster retro-Diels–Alder kinetics. Moreover, it was proved that isomerization from the endo to the exo diastereomer is preceded by a retro-Diels–Alder reaction of the endo adduct. The presence of a nucleophile in the mixture confirmed this result. This study allowed the highlighting of different parameters of the Diels–Alder reaction to obtain as much endo adduct as possible, and a fast and/or full retro-Diels–Alder reaction of this adduct.

Abstract: The reactions between fifteen carbonyl oxides and water have been investigated with the aim of contributing to a better understanding of the effects of the substituents in the reactivity of carbonyl oxides We have employed density functional theory and large scale ab initio methods (CCSD(T), CASSCF, and CASPT2), combined with transition state theory, to investigate the addition of water to carbonyl oxide and, for those carbonyl oxides having a methyl substituent in syn, the hydrogen transfer from the methyl group to the terminal oxygen of carbonyl oxide In this case, the water acts as a catalyst and this reaction can contribute to the atmospheric formation of a hydroxyl radical Carbonyl oxides with electron withdrawing substituents and zwitterionic character have low energy barriers and react fast, whereas carbonyl oxides with electron releasing substituents have high energy barriers and react slowly The position of the substituents plays also an important role and carbonyl oxides having a hydrogen atom substituent in syn react faster than carbonyl oxides having a hydrogen atom substituent in anti The differences in the reactivity of different substituted carbonyl oxides raise up to ten orders of magnitude and the branching ratios for the two different reactions investigated are also reported