Parallelism between charge redistribution and delocalization. Applications to organic reactions



The study is devoted to interrelations between two perturbative expansions for molecules and molecular systems, namely between terms of power series for one-electron density matrices on the one hand, and those for respective representation matrices of non-canonical (localized) molecular orbitals (MOs) on the other hand, as well as to the relevant implications. As the most outstanding example of the latter, simple proportionalities are established between alterations in populations of basis orbitals due to chemical interaction and delocalization coefficients of respective localized MOs (LMOs). The proof of these proportionalities is valid for members of power series to within the fifth order inclusive that were shown previously to be sufficient for investigations of the most important organic reactions. As a result, classical interpretations of early stages of these reactions in terms of shifts of respective localized pairs of electrons (cf. the so-called ‘curly arrow chemistry’) acquire a quantum-chemical support. Moreover, the results of the present study allow comparisons of relative extents of delocalization of LMOs for alternative routes of the same process. On this basis, predominant (allowed) routes of organic reactions are shown to be characterized by enhanced delocalization of respective principal pairs of electrons as compared to alternative (forbidden) routes. Raktažodžiai: localized molecular orbitals, Brillouin theorem, organic reactions, delocalization, curly arrow chemistry
Atoms and Molecules