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Understanding the mechanism of the decomposition reaction of nitroethyl benzoate through the Molecular Electron Density Theory

Research paper by Agnieszka Kącka-Zych, Luis R. Domingo, Mar Ríos-Gutiérrez, Radomir Jasiński

Indexed on: 26 Oct '17Published on: 20 Oct '17Published in: Theoretical Chemistry Accounts



Abstract

The molecular mechanism of the decomposition reaction of nitroethyl benzoate (NEB) 1 yielding nitroethylene 2 and benzoic acid 3 has been studied within the Molecular Electron Density Theory (MEDT) using DFT methods at the B3LYP/6-31G(d) computational level. This decomposition reaction takes place through a one-step mechanism. Bonding Evolution Theory (BET) analysis of this reaction provides a complete characterisation of the electron density changes along the reaction. The reaction begins through the synchronous rupture of the O–C and C–H single bonds of NEB 1. Interestingly, while the rupture of the O–C single bond takes place heterolytically, that of the C5–H6 one takes place homolytically, yielding the formation of a pseudoradical hydrogen atom. These changes, which demand a high energy cost of 37.1 kcal mol−1, are responsible for the high activation energy associated with this decomposition reaction. Formation of the C–C double bond present in nitroethylene 2 takes place at the end of the reaction. The six differentiated phases in which the IRC associated with this reaction is divided clearly point out its non-concerted nature, thus ruling out the proposed pericyclic mechanism. This reaction, whose associated TS presents a more or less distorted six-membered cyclic structure in which all atoms may not necessarily be bound, is categorised as a pseudocyclic reaction.