Recently, Chiang's group have prepared water-soluble polyhydroxylated C60 derivatives (Fullerenols) in fuming sulfuric acid via hydrolysis of polycyclosulfated precursors. A suggested reaction mechanism is proposed. The calculation of different isomers of C60(OH)6 and C60(OH)12 fullerenols has been carried out using the semiempirical MNDO and MM2 methods with two different approaches:
1.(a) consideration of the geometries and thermodynamic stabilities;
2.(b) consideration of the cyclosulfation and hydrolysis reaction mechanisms.
For (a), the double bonds in the pentagon lead to a decrease in the electron delocalization energy. Thus, the ΔHfO values of fullerenol are predicted to increase for each double bond placed in the pentagon for these fullerenols. According to the ΔHfo values, the most stable structures of C60(OH)6 and C60(OH)12 with externally bound hydroxyl groups have been generated, with Cs and S6 symmetries respectively. The ΔHfOvalues for these fullerenols are 503 kcal mol−1 (C60(OH)6) and 131.8 kcal mol−1 (C60(OH)12). According to the geometric structure of C60(OH)6 and C60(OH)12 fullerenol, multi-hydroxy additions follow 1,2- or 1,4- addition to a cyclohexatriene. For (b) the most likely products in this reaction are C60(OH)6 (Cs) and C60(OH)12 (S6), whose ΔHfOvalues are 573 and 141.5 kcal mol−1, respectively. These stable structures could contain exact hydroxyl group sites in C60, and they may be helpful in the investigation of the physical properties of polymers or other groups substituted onto fullerenols (called star-like polymers).
Journal of Molecular Structure : Theochem 391(1-2), pp.179-187