Abstract: The structures and stabilities of all 1-2, 1-4 and 1-6 hydrogen adducts of C₅₉HN were studied by using semiempirical MNDO, AMIand 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 Catom of the fullerene skeleton with an Natom, the regioselectivity of the carbon cage has been changed. According to the result of frequency analysis, we have predicted the IRspectrum of the most stable isomer.

Key words: C₅₉H₃N, Semi-empirical methods, Relative stabilities, Structures of isomers