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Is tetramethyleneethane a ground state triplet?

Chakrabarti, Aparna and Albert, IDL and Ramasesha, S and Lalitha, S and Chandrasekhar, Jayaraman (1993) Is tetramethyleneethane a ground state triplet? In: Proceedings of the Indian Academy of Sciences - Chemical Sciences, 105 (1). pp. 53-62.

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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-π 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.

Item Type: Journal Article
Publication: Proceedings of the Indian Academy of Sciences - Chemical Sciences
Publisher: Indian Academy of Sciences
Additional Information: Copyright of this article belongs to Indian Academy of Sciences.
Keywords: Tetramethyleneethane;biradical;singlet;triplet gap;MO calculations;electronic structure.
Department/Centre: Division of Chemical Sciences > Organic Chemistry
Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited: 11 Feb 2011 06:23
Last Modified: 11 Feb 2011 06:23
URI: http://eprints.iisc.ac.in/id/eprint/35521

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