富勒烯衍生物C50X(X=SiH2, PH, S)的结构及稳定性的理论研究

用从头算HF/3-21G方法研究了C50的环加成衍生物C50X(X=SiH2, PH, S)所有可能的异构体的结构与稳定性, 计算结果表明, SiH2基团、PH基团与S原子在C50上环加成的优先加成位置相同, 都为C3—C4类键和C4—C4类键, 并且相应形成5,6]-闭环和5,5]-闭环结构的最稳定异构体; 决定C50X(X=SiH2, PH, S)各异构体稳定性的主要因素, 因加成位置以及发生加成反应的C—C键的单双键类型的不同, 可能是张力、共轭效应或者二者的共同作用. 进一步比较了C50X(X=SiH2, PH, S)与C50X(X=CH2, NH, O)的结构和稳定性等, 并总结出规律性的结论, 即加成原子的大小和加成位置C—C键的类型是影响形成开环或闭环结构的C50环加成衍生物的两种主要因素.

Theoretical Study of Structure and Stability of Fuilerene Derivatives C50X (X=SiH2, PH, S)

The structure and stability of all possible isomers of C50X(X=SiH2, PH, S) were investigated by ab initio HF/3-21G calculations. The calculation results indicate that the preferred position for cycloaddition of SiH2, PH, and S on C50 is consistent, i.e. on the C3—C4 and C4—C4 sites of C50, and the resultant most stable cycloaddition isomers are 5,6]-closed and 5,5]-closed structures. The main driving force governing the stability of the C50X(X=SiH2, PH, S) isomers is the strain, or the conjugative effect, or the combination of strain and conjugative effect, depending on the addition positions and the types of the attacked C—C bonds. Further, the structures and stabilities of C50X(X=SiH2, PH, S) are compared with those of the C50X(X=CH2, NH, O), and a general conclusion are drawn: the size of the attacking atom and the type of the attacked C—C bond are two decisive factors for the formation of open or closed structure of the C50X isomer.