Symmetry numbers and chemical reaction rates

Antonio Fernández-Ramos, Benjamin A. Ellingson, Rubén Meana-Pañeda, Jorge M.C. Marques, Donald G. Truhlar

Research output: Contribution to journalArticlepeer-review

208 Scopus citations


This article shows how to evaluate rotational symmetry numbers for different molecular configurations and how to apply them to transition state theory. In general, the symmetry number is given by the ratio of the reactant and transition state rotational symmetry numbers. However, special care is advised in the evaluation of symmetry numbers in the following situations: (i) if the reaction is symmetric, (ii) if reactants and/or transition states are chiral, (iii) if the reaction has multiple conformers for reactants and/or transition states and, (iv) if there is an internal rotation of part of the molecular system. All these four situations are treated systematically and analyzed in detail in the present article. We also include a large number of examples to clarify some complicated situations, and in the last section we discuss an example involving an achiral diasteroisomer.

Original languageEnglish (US)
Pages (from-to)813-826
Number of pages14
JournalTheoretical Chemistry Accounts
Issue number4
StatePublished - Oct 2007


  • Chemical reactions
  • Chiral molecules
  • Internal rotation
  • Multiple conformers
  • Symmetry numbers
  • Transition state theory

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