Pyracylene transformation

As the enantiomers of D2-C84 can formally be interconverted by Stone-Wales pyracylene rearrangements91,92 via the achiral D2d-Cs4, they were ideal candidates to study the activation barrier of this transformation. However, taking into account the loss of material through decomposition, neither heating (600/700°C) nor irradiation (X = 193 nm) led to a significant loss of optical activity in samples of enantiomerically enriched D2-Cm or D2-C76. This shows that the activation barrier amounts to at least 83 kcalmol-1 for a potential Stone-Wales rearrangement.5... 

Stone and Wales examined rotation of C-C bonds in various fullerene structures using approximate Huckel calculations. The 90° rotation of C-C bond in fullerene is called Stone-Wales (SW) or pyracylene rearrangement (O Fig. 22-15) (Stone and Wales 1986). Austin et al. reported that 94% of all fullerene Ceo isomers can rearrange to Buckminsterfullerene by SW transformation (Austin et al. 1995). The C78 cage represents the smallest fullerene in which SW rearrangement can give stable IPR isomers C7s 5 (D3/,) <- C7s 3 (C2v) Cjr.l (C2v) C7s 4 (D3 ,) where... 

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