Photochemistry of Hydroxycyclohexadienyl Radicals : 2 Substituted Phenols
| Autor: | Sumiyoshi, Takashi |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2018 |
| Předmět: | |
| Zdroj: | 日本医療大学紀要. 4:25-36 |
| ISSN: | 2189-2830 |
| Popis: | 水溶液中でメチル，メトキシ置換フェノール類のOH付加体（ヒドロキシシクロヘキサジエニルラジカル）の光化学反応をパルスラジオリシスとレーザーフラッシュフォトリシスを組み合わせた方法により観測し，環炭素上の電荷密度を半経験的分子軌道法（MOPAC）で求め，置換基の位置が光化学反応機構に与える効果を調べた．OH付加体の光励起により量子収量0.11－0.16の永続的な光ブリーチが観測された．置換基のオルト-パラ配向性により置換基を有しない環炭素が比較的大きな負電荷密度を持つフェノール類の場合にはフェノキシルラジカルが優先的に生成する．一方，置換基の配置による電荷密度の変化が小さいフェノール類の場合は，メトキシ基からの水素引き抜き反応が競合的に起こることが，関連する反応のエンタルピー変化や分光学的考察から明らかになった． Photochemical reactions of OH-adducts（hydroxycyclohexadienyl radicals）of a variety of methyl- and methoxy-substituted phenols in aqueous solutions have been studied using the combined pulse radiolysislaser flash photolysis technique, and the effects of the position of substituents on the photochemical reaction mechanism have been investigated based on the charge distribution on ring carbons estimated by the semi-empirical molecular orbital method（MOPAC）．Upon laser flash photolysis of the OHadducts permanent photobleaching has been observed with quantum yields of 0.11－0.16. In the case of phenols which have higher electron density on the ring carbons due to the ortho–para clirecting nature, the photobleaching of OH-adducts leads exclusively to phenoxyl radicals formation. On the other hand, it is strongly suggested for phenols with relatively small charge localization changes on ring carbons, hydrogen abstraction from methoxy groups occurs competitively, based on the consideration of enthalpy changes of reactions concerned and the spectral characteristics of transient species. |
| Databáze: | OpenAIRE |
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