C_(59)H_3N异构体的结构与稳定性的理论研究

Studies on the Structures and Stabilities of C_(59)H_3N Isomers

分别用MNDO,AM1和PM3三种半经验方法对C_(59)HN所有1-2,1-4和1-6氢加成物C_(59)H_3N的异构体进行几何构型全优化,结合频率分析及HF/6-31G单点能计算,确定了各异构体的基态结构及其相对稳定性,计算结果表明,C_(59)HN氢加成物的立体选择性规律与C_(60)和C_(60)H_2的不同,最稳定异构体不是1-2加成物,而是1-4加成的6,18-或12,15-异构体,次稳定异构体为1-2加成物,三种半经验方法计算得到的两者能量差为13～15kJ/mol,N原子取代碳笼骨架C原子后,改变了碳笼氢加成物的立体选择性规律。

The structures and stabilities of all 1-2, 1-4 and 1-6 hydrogen adducts of C59HN were studied by using semiempirical MNDO, AMI and PM3 methods. In order to verify the reliability of the semiem-pirical methods, some energetically favored isomers of these hydrogen adducts were calculated by using HF/6-31G for single-point energy. The calculation results indicate that in general, 1-2 adducts are more stable than 1-4 adducts and far more stable than 1-6 adducts. However, the most stable isomer is 6,18- or 12,15- isomer which is a 1-4 adduct and the second most stable isomer is a 1-2 adduct, calculated by the three semiempirical methods the energy of the former is lower than that of the latter by 13-15 kJ/mol. The computed nucleus independent chemical shifts(NICS) indicate that the more stable the isomer, the more aromatic the molecule, aromaticity may be the primary factor governing the stabilities of C59H3N isomers. By replacing one C atom of the fullerene skeleton with an N atom, the regioselectivity of the carbon cage has been changed. According to the result of frequency analysis, we have predicted the IR spectrum of the most stable isomer.