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Electron reorganization in allowed and forbidden pericyclic reactions: multicenter bond indices as a measure of aromaticity and/or anti‐aromaticity in transition states of pericyclic electrocyclizations
Author(s) -
Mandado Marcos,
Ponec Robert
Publication year - 2009
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.1589
Subject(s) - pericyclic reaction , chemistry , delocalized electron , aromaticity , electrocyclic reaction , electron delocalization , computational chemistry , transition state , photochemistry , ring (chemistry) , molecule , organic chemistry , catalysis
The multicenter bond indices (MCI), recently proposed as quantitative measures of cyclic delocalization in aromatic systems, have been applied to characterize the differences in the nature of the electron reorganization in a series of allowed and forbidden electrocyclic reactions of linear neutral polyenes of general formula C n H n +2 and related charged systems of formula C n H n +2 (+) and C n H n +2 (−) for n ranging from 4 to 7. The proposed methodology, which is based on the monitoring of the variation of the extent of cyclic delocalization along the concerted reaction paths, is shown to be completely consistent with the empirical Evans/Dewar classification anticipating aromatic transition states for allowed and anti‐aromatic transition states for forbidden electrocyclic reactions. Although the study reports the results of the analysis of electron reorganization just for the above‐mentioned particular class of electrocyclic reactions, the proposed approach is completely general and its conclusions remain valid for any pericyclic reaction. Copyright © 2009 John Wiley & Sons, Ltd.