The perfectly resonating state: A chemical model for the transition state

Avital Shurki*, Sason Shaik

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


This paper describes the perfectly resonating state (PRS) as a chemical model for the saddle point (the "transition state"). The perfectly resonating state is typified by a pairwise resonance (or avoided crossing) between two of the principal valence bond structures which describe the electronic structure of the reaction complex. A search procedure of the PRS is devised within the same quantum chemical scheme which locates the saddle point. The idea is applied to Menschutkin and anionic SN2 reactions which span a wide range (> 100 kcal mol-1) of reaction energy. A topological property of all the reactions is the "phase diagram" appearance of the potential energy surface, where the PRS situations, which define lines with one degree of freedom, meet at a single point: the globally resonating state that possesses no degrees of freedom. In all cases the saddle point is found to be located near the minimum energy PRS that is typified by perfect resonance between the covalent valence bond structures.

Original languageAmerican English
Pages (from-to)37-45
Number of pages9
JournalJournal of Molecular Structure: THEOCHEM
Issue number1-2
StatePublished - 9 Feb 1998

Bibliographical note

Funding Information:
This work was supportedb y a grant from the Israel Science Foundation (ISF).


  • Avoided crossing
  • Perfectly resonating state
  • S2 reactions
  • Saddle point
  • Transition state


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