sp^3杂化碳中心自由基进攻腈基环合成反应的理论研究

Theoretical investigation on the cyclization reaction of sp～3-hybridized C-central radical onto nitriles

应用密度泛函理论对4个sp3杂化的碳中心自由基进攻腈基的环合成反应做了理论研究。结果表明,生成五元环过程在动力学和热力学方面均是有利的过程,而生成六元环的过程是难于进行的。反应过程的难易可以用进攻角度在反应过程中的变化来定性地判断,并用以定性地解释Baldwin规则的结论。同时,对于6-endo-dig和5-exo-dig过程,C中心自由基的自旋电子密度高低对进攻势垒有较大的影响。此外,研究也表明,吸热反应的热力学过程会使动力学势垒升高,而放热反应则可以降低反应的动力学势垒。

Four cyclization reactions of sp^3-hybridized C-central radical onto nitriles were investigated by use of density functional theory. The computation results show that the channel leading to the five-membered cyclic product is kinetically and thermodynamically more favorable than the pathway towards six-membered ring product. That if it is favorable can be evaluated by the change of the attacking angle in the reaction trajectory, and the kind of reaction can be qualitatively explained by Baldwin rule. Also, for the 6-endo-dig and 5-exo-dig reaction pathways, the spin electron density should be responsible for the kinetic barrier. Furthermore, the computed results also indicated that an endothermic process can increase the reaction kinetic barrier, while an exothermic process can decrease it.