Aromaticity in Pericyclic Transition State Structures? A Critical Rationalisation Based on the Topological Analysis of Electron Density

Luis R. Domingo, Mar Ríos-Gutiérrez, Eduardo Chamorro, Patricia Pérez

Research output: Contribution to journalArticlepeer-review

18 Citations (Scopus)

Abstract

The nature of the electron delocalisation pattern within a cyclic structure, i. e. the aromatic character, is examined for six-membered pseudocyclic transition state structures (TSs) involved in five representative examples of so-called pericyclic reactions. Results of the electron localisation function (ELF) and the quantum theory of atoms in molecules (QTAIM) analyses of the electron density evidence that in four of the cases, at least one pair of atoms are not bound at the TS configuration, thus precluding a possible cyclic conjugation. These findings make it possible to rule out the aromatic character of these TSs. High values of the synchronicity Sy index at the TSs contrast with the bonding changes evidenced by ELF topological analysis. The magnitude of the nucleus independent chemical shift (NICS) computed for the five TSs becomes much more negative than that of the reference system, benzene, with no obvious relation to the strong evidence of the pattern of delocalisation revealed by the topological analysis of ELF and QTAIM for each TS. The topology of the anisotropy of current induced density (ACID) at each TS reveals the actual existence of strong non-symmetrical patterns of electron delocalisation of the five TSs.

Original languageEnglish
Pages (from-to)6026-6039
Number of pages14
JournalChemistrySelect
Volume1
Issue number18
DOIs
Publication statusPublished - 1 Jan 2016

Keywords

  • aromaticity
  • electron density
  • electron localisation function
  • pseudocyclic reactions
  • quantum theory of atoms in molecules

ASJC Scopus subject areas

  • Chemistry(all)

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