Photolysis of 1B in argon-saturated solutions yields 4B and releases methanol. Laser flash photolysis of 1B shows formation of biradical 2B, which has a lifetime of ~50 ns and a λmax at 330 nm. Biradical 2B undergoes an intersystem crossing to form photoenols E-3B and Z-3B with a λmax at 390 nm. Laser flash photolysis shows that the lifetimes of E-3B and Z-3B are affected by the solvent. Density functional theory calculations demonstrate that the transition-state barrier for a 1,5-H atom shift from Z-3B to regenerate 1B is affected by the ortho-alkyl substituents, whereas the stereoelectronics of the alkyl substituent affect the transition-state barrier of E-3B as it undergoes electrocyclic ring closure to form 4B. The photoreactivity of 1B was compared with its analogous methyl and isopropyl derivatives 1A and 1C, respectively, to better estimate the effect of the alkyl substituent on reactivity.
1B 在氩气饱和溶液中光解产生 4B,并释放出甲醇。1B 的激光闪烁光解显示出双拉子 2B 的形成,双拉子 2B 的寿命约为 50 毫微秒,λmax 波长为 330 纳米。双环戊二烯 2B 经过系统间交叉形成光烯醇 E-3B 和 Z-3B,其 λmax 为 390 nm。激光闪烁光解表明,E-3B 和 Z-3B 的寿命受溶剂影响。密度泛函理论计算表明,1,5-H 原子从 Z-3B 转移到再生 1B 的过渡态势垒受到正烷基取代基的影响,而烷基取代基的立体电子学则会影响 E-3B 的过渡态势垒,因为 E-3B 会发生电环闭环生成 4B。为了更好地估计烷基取代基对反应活性的影响,我们将 1B 的光反应活性分别与其类似的甲基和异丙基衍生物 1A 和 1C 进行了比较。