Electrophilicity parameters theoretical studies

A systematic and intensive theoretical study of reactivity has been reported by Brown and his colleagues,8,115,139-142 who discussed the reactivity of pyridine, quinoline, and isoquinoline in terms of localization energies. They investigated the values of these indices, first of all for electrophilic substitution, with regard to the value of the Coulomb integral of the heteroatom orbital and the orbitals adjacent to it (auxiliary inductive parameters). They demonstrated that the course of electrophilic substitution can be estimated from theoretical reactivity indices if 77-electron densities are used for reactions that occur readily and localization energies for those occurring only reluctantly. 

An L-shaped arrangement of bromine atoms has been identified by spectroscopy and theoretical studies on the 2 1 71-complex (8) generated by electrophilic bromination of tetraneopentylethylene (6). The reaction stops at the stage (8) which, for the first time, allowed its detection and determination of its thermodynamic parameters by UV spectroscopy (Scheme 1). Theoretical calculations predict an alkene-Br2 Br2 rather than the Br2-alkene-Br2 structure.22... 

A DFT study addressed the relationship between electrophilicity and electro-fugality. A number of descriptors obtained by semi-empirical and DFT methods were evaluated for estimations of the Mayr electrophilicity parameters. For a set of 64 electrophiles, good correlations were found using reactivity descriptors calculated by the PM6 semi-empirical and DFT methods. Rate constants for reactions of amines and benzhydrylium ions were calculated using various theoretical methods. A combined ONIOM/DFT approach gave good agreement with experiment. 

Several reactivity parameters adopted from theoretical chemistry have been used to predict the position at which electrophilic reagents will attack higher aromatics l37). The applicability of such parameters to the non-planar hexahelicene was studied qualitatively in bromination, nitration and acetylation reactions 169), and in a quantitative way in the protiodetritiation of the eight monotritiohexahelicenes 170). 

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