Aromatization Energy and Strain Energy of Buckminsterfullerene from Homodesmotic Reactions

The amount of aromatic stabilization of C60 fullerene (E aroma) and the amount of its destabilizing strain effect (E strain) are unknown quantities because both are intimately connected and difficult to separate. Based on experimentally known transformation of C60H30 to C60 and conversion of a polycyclic aromatic hydrocarbon C60H20 to the nonaromatic linear conjugated C60H62, new homodesmotic reaction schemes have been proposed to evaluate E aroma and E strain. The E aroma values obtained at M06L/6-311G­(d,p), M062X/6-311G­(d,p), and B3LYP-D3/6-311G­(d,p) levels of density functional theory are 122.3, 169.8, and 152.4 kcal/mol, respectively, whereas E strain values at these levels are 327.3, 382.0, and 381.4 kcal/mol, respectively. These data suggest that a CC bond of C60 is destabilized by ∼2.28–2.54 kcal/mol compared to that of benzene, and this minor energetic effect explains the existence of C60 as a stable molecule.