Alkanethioimidoyl Radicals: Evaluation of β-Scission Rates and of Cyclization onto <i>S</i>-Alkenyl Substituents
作者:Matteo Minozzi、Daniele Nanni、John C. Walton
DOI:10.1021/jo0353637
日期:2004.3.1
Thioimidoyl radicals were generated by addition of alkylsulfanyl radicals to alkyl isonitriles and were characterized by electron paramagnetic resonance (EPR) spectroscopy. The β-scissions of their C•S−C bonds were studied by variable-temperature EPR spectroscopy and the fragmentation rate constants and activation energies were calculated. The scission rates depend on the stability of the released alkyl radicals
硫代亚氨基基团是通过将烷基硫基基团加到烷基异腈中而生成的,并通过电子顺磁共振(EPR)光谱进行了表征。通过变温EPR光谱研究了它们的C • S–C键的β断裂,并计算了断裂速率常数和活化能。断裂速率取决于所释放的烷基的稳定性,但是在任何情况下,在室温下,该过程都是快速的。收集到的类似氧基亚酰亚胺基的数据表明,与类似的硫代酰亚胺基相比,它们的裂解略慢。EPR无法研究硒代亚酰胺的断裂速率,而无法通过理论计算进行评估。EPR实验还启用了β分裂和5-exo待测定的两个S-丁-3-烯基取代的亚甲基酰基的闭环速率常数,表明环化仅在低温下盛行。密度泛函理论(DFT)理论计算预测,断裂过程优先发生在亚氨基的s-顺式旋转异构体(X-C键)上。硫代和硒代亚氨基(而不是氧亚氨基)更喜欢s-反式构象,因此它们的断裂涉及事先围绕X-C键的旋转。