An extremely short-lived 1,4-biradical as intermediate in the photo-cycloaddition reactions of triplet state aromatic thiones with allenes
作者:Johan Kamphuis、Hendrik J. T. Bos、Robert J. Visser、Bert H. Huizer、Cyril A. G. O. Varma
DOI:10.1039/p29860001867
日期:——
of the aromatic thione in the thermal reaction with an allene and log ka depend linearly on the ionization energy of the allene. Previous suggestions that the 1,4-biradical has a triplet state exciplex as precursor are rejected on the basis of the similarity of these relations and because of the fact that there is no difference in the effect on ka and kt caused by deuteriation of the allene.
通过以308 nm激光闪光引发反应并遵循纳秒级的瞬态uv-可见光吸收,研究了x吨9-硫酮,硫代二苯甲酮和噻吨9-硫酮与丙二烯的光化学反应。在波长范围320 <λ<800nm的存在只能从硫酮在其最低三重态引起的瞬态吸收Ť 1(Ñ π*)。由Stern–Volmer曲线确定了在此状态下用丙二烯淬灭硫酮的速率常数k a。可以用NN清除作为反应中间体的1,4-双自由基′-二甲基-4,4′-联吡啶二氯化物(甲基紫精,MV)。已经确定了由清除产生的甲基紫精自由基阳离子MVRC的产率与MV浓度的关系。由此,对于1,4-双自由基(8),寿命为90 ps 。短寿命归因于两个不成对电子在硫原子上的大自旋密度,从而导致有效的局部自旋-轨道耦合。与烯丙基的热反应中芳族硫酮消失的速率常数k t的对数和log k a线性依赖于丙二烯的电离能。上一页建议,1,4-双基具有三重态激基复合物的前体,这些关系的相似性的基础上