Stone-Wales rearrangements

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... 

Another transformation of one aromatic compound to another is the Stone-Wales rearrangement of pyracyclene (113), which is a bond-switching reaction. The rearrangement of bifluorenylidene (114) to dibenzo[g,p] chrysene (115) occurs at temperatures as low as 400° C and is accelerated in the presence of decomposing iodomethane, a convenient source of methyl radicals. This result suggested a... 

In summary, based on the available experimental and theoretical data, neither the existence nor the nonexistence of non-carbon fullerene polymorphs can be concluded. However, since sp bonding is energetically more favorable for Cn than for SIn, in the latter there are no caps and no plane structures which play a crucial role in fullerene formation. It seems that the mechanism of formation of such complexes for carbon and silicon is different. Taking into account the fact that the fullerene structure is not the global minimum for either carbon or silicon and in combination with the observable tendency of silicon clusters to have a spherical form, one can assume that under certain conditions processes similar to Stone-Wales rearrangement from polycyclic carbon structures to fullerene is also possible for silicon. Currently there is no common opinion on this issue. However, in addition to the notes about direct syntheses of non-carbon fullerenes, it is possible to specify some new synthetic approaches to the formation of silicon clusters. 

Fig. 17. Generalized Stone-Wales rearrangement the first row indicates the pyracylene automerization, the next two rows the generalization for proper fullerenes, and the last two rows the generalization for any size of polygons of the cage.

There are other possible fairly local rearrangement processes conceivable, such as in Figure 22, which has been suggested by CurP as a possibility to correspond to a physically realized mechanism. Moreover, it interconnects " all 1812 fullerenes of 60 atoms, though not so for 70-atom fullerenes. Still this is much better than for the ordinary Stone-Wales rearrangement. There are several other at least formally conceivably rearrangement processes. 

Stone-Wales Rearrangement on Picosecond and Nanosecond Timescales... 

Fig. 7.10 Illustration of Stone-Wales rearrangement (SWR) and fragmentation from the non-IPR structure C to F via D. Fragmentation along the broken line is dynamically unfavorable. The kinetic energies of the six carbons with filled circles are monitored as a local eneigy that can be used for SWR. See Fig. 7.12...

Fig. 7.11 Snapshots of Stone-Wales rearrangement in 606 ps after the initial injection of 63 eV into the ag(l) mode. The single bonds C2-C3 and C2-C4 cleave, and then the double bond between Cl and C2 rotates. The bond network structure of C(,o is changed to a non-IPR structure...

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