Factors affecting the selection of products from a photochemically generated singlet biradical
作者:David A. Broyles、Barry K. Carpenter
DOI:10.1039/b501422k
日期:——
The chemistries of a monoradical of the ultrafast "radical-clock" type and a structurally related singlet biradical, generated by Norrish type II photochemistry, are compared. The monoradical is found to undergo the characteristic ring-opening reaction of its class at about 10(10) s(-1) at room temperature. However, the singlet biradical shows no evidence of the analogous ring-opening reaction. The contrasting
比较了由Norrish II型光化学产生的超快“自由基钟”型单自由基和与结构相关的单线双自由基的化学性质。发现该自由基在室温下在约10(10)s(-1)时经历同类的特征性开环反应。但是,单线态双自由基没有显示类似开环反应的证据。形成对比的化学反应不仅可以追溯到两个中间体的电子结构的根本差异,还可以追溯到在开环过程中仅双自由基所必须经历的空间相互作用。尽管位阻的大小很小(估计为15-20 kJ mol(-1)),但足以终止反应,因为双自由基还具有其他易于形成的产物反应。