• Fulltext

       

        Click here to view fulltext PDF


      Permanent link:
      https://www.ias.ac.in/article/fulltext/jcsc/105/01/0053-0062

    • Keywords

       

      Tetramethyleneethane; biradical; singlet-triplet gap; MO calculations; electronic structure

    • Abstract

       

      We have examined a number of possible ways by which tetramethyleneethane (TME) can be a ground state triplet, as claimed by experimental studies, in violation of Ovchinnikov’s theorem for alternant hydrocarbons of equal bond lengths. Model exact π calculations of the low-lying states of TME, 3,4-dimethylenefuran and 3,4-dimethylenepyrrole were carried out using a diagrammatic valence bond approach. The calculations failed to yield a triplet ground state even after (a) tuning of electron correlation, (b) breaking alternancy symmetry, and (c) allowing for geometric distortions. In contrast to earlier studies of fine structure constants in other conjugated systems, the computedD andE values of all the low-lying triplet states of TME for various geometries are at least an order of magnitude different from the experimentally reported values. Incorporation of σ mixing by means of UHF MNDO calculations is found to favour a singlet ground state even further. A reinterpretation of the experimental results of TME is therefore suggested to resolve the conflict.

    • Author Affiliations

       

      Aparna Chakrabarti1 I D L Albert1 S Ramasesha1 S Lalitha2 Jayaraman Chandrasekhar2

      1. Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore - 560 012, India
      2. Department of Organic Chemistry, Indian Institute of Science, Bangalore - 560 012, India
    • Dates

       
  • Journal of Chemical Sciences | News

© 2021-2022 Indian Academy of Sciences, Bengaluru.