On the pairing of molecular orbital energy levels of heteroconjugated molecules

Ivan Gutman*, Swarna M. Patra, Rama K. Mishra

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The pairing theorem (discovered by Coulson and Rushbrooke in 1940) predicts pairing of the molecular orbital energy levels of alternant hydrocarbons, as calculated within the Hückel molecular orbital (HMO) model. In the general case, the pairing theorem does not apply to nonalternant hydrocarbons or alternant conjugated systems containing heteroatoms. It was recently observed that, in certain heteroconjugated molecules (both alternant and nonalternant), some HMO energy levels remain paired irrespective of the nature of the heteroatoms, i.e., irrespective of the values of the HMO parameters h and k. We now provide an explanation of this regularity.

Original languageEnglish (US)
Pages (from-to)25-30
Number of pages6
JournalJournal of the Serbian Chemical Society
Issue number1
StatePublished - 1998


  • Chemical graph theory
  • Heteroconjugated molecules
  • Hückel molecular orbital theory
  • Pairing theorem

ASJC Scopus subject areas

  • Chemistry(all)


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