Most stable structure of fullerene[20] and its novel activity toward addition of alkene: a theoretical study

Structures and stabilities of fullerene C20 and C20- have been investigated by the density functional theory and CCSD(T) calculations. In consideration of the Jahn-Teller distortion of Ih-symmetric C20, possible subgroup symmetries have been used in the full geometry optimization. On the basis of relative energetics, vibrational analyses, and electron affinities, fullerenes C20 and C20- have most stable D2h and Ci structures, respectively. The controversy on the relative stability of fullerene[20] arises from the use of different subgroups in calculation and the basis set dependence in vibrational analysis. Predicted nucleus-independent chemical shift values show that the most stable fullerene C20 and its derivatives C20(C2H2)n and C20(C2H4)n (n=1-3) exhibit remarkable aromaticity, while C20(C2H2)4 and C20(C2H4)4 have no spherical aromaticity. The C20 (D2h) cage has remarkable activity toward the addition of olefin, and such feasibility of the addition reaction is ascribed to strong bonding interactions among frontier molecular orbitals from C20 and olefin. Calculations indicate that both C20(C2H2)n and C20(C2H4)n have similar features in electronic spectra.