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Unveiling substituent effects in [3+2] cycloaddition reactions of benzonitrile N-oxide and benzylideneanilines from the molecular electron density theory perspective

Mondal Asmita, Mohammad-Salim Haydar A., Acharjee Nivedita

Scientiae Radices

2023

Vol. 2, Iss. 1

75--92

The zw- type [3+2] cycloaddition (32CA) reactions of benzonitrile N-oxide with a series of substituted benzylideneanilines have been studied within the Molecular Electron Density Theory (MEDT) at the B3LYP/6-31G(d) computational level. The presence of dimethylamino and methoxy substituents in the aromatic rings of benzylideneaniline makes the reaction more facile relative to the unsubstituted one, while the electron withdrawing nitro substituents relatively induce minimal changes in the energy profile complying with the experimentally observed reaction rates. The presence of non-bonding electron density at the nitrogen atom and the formation of pseudoradical centre at the carbon atom of benzonitrile N-oxide characterise the difference in electronic structure of the TSs relative to the reagents, while the topological analysis of the electron localization function (ELF) and the atoms-in-molecules (AIM) reveal no covalent bond formation at the early TSs. The present MEDT study analyses the experimentally observed substituent effects and complete regioselectivity in the studied 32CA reactions.

Zastosowanie topologicznej analizy funkcji lokalizacji elektronów (ELF) do badania struktury elektronowej molekuł

Berski Sławomir

Wiadomości Chemiczne

2019

[Z] 73, 1-2

5--32

In 1990 Becke and Edgecombe proposed a description of electron localisation in atomic and molecular systems based on the formalism of the second-order reduced density matrices in the form of Electron Localisation Function, ELF. In 1994 Silvi and Savin, of Pierre and Marie Curie University in Paris, presented how to describe local electronic structure of chemical bonds and how to classify them based on topological analysis of ELF, thereby used the methodology developed in 1970s by Bader to study the topology of molecular electron density. In 2003 Popelier formulated a capacious methodology: „Quantum Chemical Topology”, which groups under one umbrella all methods of computational quantum chemistry using concepts such as: attractor, basin of attractor, gradient vector field, gradient path, and in 2010 a conference was held, entitled: „Twenty Years ELF” referring to the 20 year period of reserach using the topological analysis of ELF. The author, since 1994 working – in collaboration with Prof. Silvi – on the application of the topological analysis of ELF for elucidation of electronic structure of molecules and mechanism of chemical reactions, discusses the methodology of research and presents example of the results concerning the nature of chemical bonding in molecular systems.