Studies of Reaction Mechanisms by All-valence Electron Semi-Empirical SCF MO Theories. VIII. Electronic Structure and Valence Isomerization of <I>syn</I>- and <I>anti</I>-Tricyclo[4.2.0.0<SUP>2,5</SUP>]octa-3,7-dienes
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概要
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The theoretical structures and heats of formation of <I>syn</I>- and <I>anti</I>-tricyclo[4.2.0.0<SUP>2,5</SUP>]octa-3,7-dienes (<B>1</B> and <B>2</B>) have been investigated by the MINDO methods. An examination of their MO's reveals that there is an extensive mixing between the highlying σ-orbitals of the four-membered rings and the ethylenic π-orbitals, which makes the highest occupied MO's devoid of any ethylenic π-character. A degenerate valence isomerization (Eq. (7)) rather than the [2+2] cycloaddition is suggested as an excited-state reaction. An intermediately facile (<I>ΔH</I><SUP>\neweq</SUP>=23.1 kcal/mol) degenerate Cope rearrangement (Eq. (1)) is predicted for <B>1</B> under thermal conditions. The transition-state structure (<B>1</B>′) and the partitioned activation energy values obtained by the MINDO/2 methods are compared with those for the Cope rearrangement of semibullvalene (<B>3</B>) and 1,5-hexadiene. The deviation from planarity of the allyl groups in <B>1</B>′ is the reason for the activation energy calculated for <B>1</B> being higher than that for <B>3</B>. The hypothetical paths from <B>1</B> to cubane in the electronic ground state are characteristic of the reaction with an anti-aromatic transition state.
- 公益社団法人 日本化学会の論文
著者
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Iwamura Hiizu
Department Of Chemistry Faculty Of Science The University Of Tokyo
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Kunii Tosiyasu
Information Science Laboratory Faculty Of Science And The Computer Center The University Of Tokyo
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Kihara Hiroshi
Department of Chemistry, Faculty of Scienc, The University of Tokyo
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Iwamura Hiizu
Department of Chemistry, Faculty of Scienc, The University of Tokyo
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Morio Kazuhiko
Department of Chemistry, Faculty of Scienc, The University of Tokyo
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