Dispersion interaction stabilizes sterically hindered double fullerenes.

By state-of-the-art quantum chemical methods, we show that for bulky functional groups like cyclohexane, [20]fullerene, dodecahedrane, and C60, the attractive dispersion interaction can have a greater impact on stereochemistry than the repulsive steric effect, making the compact isomer the more stable one. In particular, for the double C60 adduct of pentacene 1, the syn isomer should be the main product instead of the anti one inferred in the original synthesis experiment (Y. Murata et al., J. Org. Chem. 1999, 64, 3483). With and without dispersion interactions taken into account, the Gibbs energy difference ΔG(syn-anti) is -6.36 and +1.15 kcal mol(-1), respectively. This study reminds us that dispersion interactions as well as electrostatic or hyperconjugation effects, etc. can lead to some unusual stereochemical phenomena.