半片呐醇和环庚烷正离子重排反应的从头算研究

Study on rearrangement of semipinacone and cycloheptane cation with ab initio method

用HF方法,基组采用STO-3G*,分别对半片呐醇和环庚烷正离子的重排机理进行了从头算研究,计算了半片呐醇和环庚烷正离子重排过程中的各个状态的几何构型、零点能,同时对反应路径也进行了计算。得出的结论是:半片呐醇重排是环的扩大过程,在扩环过程中,N≡N逐渐远离C7,键角C7-C6-O8发生很大变化,导致C7与C1之间的距离变短,同时C1-C6之间的键长变长;而环庚烷正离子的重排则是环的缩小过程,在缩环过程中,经历了两个过渡态;首先是C1-C7的键长变长,C1-C6的键长变短,形成State2结构,然后是H17的位置移动,两面角C(7)-C(6)-C(5)-C(1)发生很大变化,产生甲基环己烷正碳离子的椅式结构。

Mechanism of rearrangement of semipinacone and cycloheptane cation were studied with HF method and STO-3G* basis set. All kinds of states in the process of rearrangement were calculated including geometry optimizing and zero point energy calculations. Meantime, the reaction coordinates were also calculated. It was concluded that rearrangement of semipinacone was a process of ring-expanding during N≡N detached from C7 and bond angle C7-C6-O8 changed greatly resulting in the distance of C7-C1 became shorter and distance of C1-C6 became longer. Whereas the rearrangement of cycloheptane cation was a process of ring-reducing which had two transition states. During its rearrangement, bond length of C1-C7 became longer and C1-C6 became shorter and thus formed geometry of State2, then H17 transformed resulting in the dihedral of C(7)-C(6)-C(5)-C (1) changed apparently and formed chair conformation of methyl hexamethylene cation.