Thermal cis-to-trans isomerization of substituted azobenzenes. II. Substituent and solvent effects.
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概要
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The thermal <I>cis</I>-to-<I>trans</I> isomerization rate of various azobenzenes was followed by means of spectrophotometric and flash photolysis techniques. For <I>para</I>-donor/<I>para</I>′-acceptor-substituted azobenzenes such as 4-nitro-4′-dimethylaminoazobenzene, the rate was distinctly accelerated, the activation energy decreasing with the increase in the polarity of solvents. Introduction of substituents in <I>para</I> positions with respect to azo group increased the rate irrespective of substituent. The effect is additive and a Hammett-type equation holds. For 4-dimethylamino-and 4-nitroazobenzenes, while the 2-methyl group accelerated the rate, the 2′-methyl group did not. The results suggest that the isomerization proceeds <I>via</I> inversion mechanism and the rate is controlled mainly by the resonance stabilization in the coplanar transition state. The inversion center for asymmetric azobenzenes is discussed.
- 公益社団法人 日本化学会の論文
著者
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Yamamoto Shunzo
Department Of Chemistry Faculty Of Science Okayama University
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Hasegawa Shigeo
Department Of Cardiology Matsudo Municipal Hospital
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Nishimura Norio
Department Of Chemistry Faculty Of Science Okayama University
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Yamanaka Hideyuki
Department of Chemistry, Faculty of Science, Okayama University
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Sueyoshi Toshinobu
Department of Chemistry, Faculty of Science, Okayama University
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Imai Etsuko
Department of Chemistry, Faculty of Science, Okayama University
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