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The principle of nonperfect synchronization: how does it apply to aromatic systems?
Author(s) -
Bernasconi C. F.
Publication year - 2004
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.810
Subject(s) - delocalized electron , chemistry , aromaticity , chemical physics , resonance (particle physics) , computational chemistry , proton , charge (physics) , molecule , atomic physics , organic chemistry , quantum mechanics , physics
According to the Principle of Nonperfect Synchronization (PNS), a product‐stabilizing factor, the development of which at the transition state lags behind bond changes, increases the intrinsic barrier of a reaction, but lowers it if it develops ahead of bond changes. Because of the generality of this principle, details of transition state structures can be deduced from comparisons of intrinsic barriers within classes of reactions. A major conclusion that has emerged from such comparisons is that reactions that lead to charge delocalization/resonance stabilized products have transition states in which the development of charge delocalization/resonance stabilization lags behind bond changes and, hence, have relatively high intrinsic barriers. This paper deals with reactions that lead to aromatic molecules or ions. The question we are asking is whether or not aromaticity follows the pattern of common resonance effects and lags behind bond changes at the transition state. Evidence based on experimentally determined intrinsic barriers of proton transfers from rhenium carbene complexes in solution, as well as that based on ab initio calculations of proton transfers in the gas phase, suggests that aromaticity development at the transition state may actually be ahead of bond changes. Copyright © 2004 John Wiley & Sons, Ltd.