Das Anushree, Lao Emily A, Gudmundsdottir Anna D
Department of Chemistry, University of Cincinnati, Cincinnati, OH.
Photochem Photobiol. 2016 May;92(3):388-98. doi: 10.1111/php.12590.
Photolysis of ester 1 in argon-saturated methanol and acetonitrile does not produce any product, whereas irradiation of 1 in oxygen-saturated methanol yields peroxide 2. Laser flash photolysis studies demonstrate that 1 undergoes intramolecular H atom abstraction to form biradical 3 (λmax ~340 nm), which intersystem crosses to form photoenols Z-4 and E-4 (λmax ~380 nm). Photoenols 4 decay by regenerating ester 1. With the aid of density functional theory calculations, it was concluded the photoenol E-4 does not undergo spontaneous lactonization or electrocyclic ring closure because the transition state barriers for these reactions are too large to compete with reketonization of E-4 to form 1.
在氩气饱和的甲醇和乙腈中，酯1的光解不产生任何产物，而在氧气饱和的甲醇中照射1则生成过氧化物2。激光闪光光解研究表明，1发生分子内氢原子夺取反应形成双自由基3（最大吸收波长约340 nm），该双自由基经系间窜越形成光烯醇Z-4和E-4（最大吸收波长约380 nm）。光烯醇4通过再生酯1而衰变。借助密度泛函理论计算得出，光烯醇E-4不会发生自发内酯化或电环化闭环反应，因为这些反应的过渡态能垒太大，无法与E-4再酮化形成1的反应竞争。
