Stone-Wales

Hawkins J M, Nambu M and Meyer A 1994 Resolution and configurational stability of the chiral fullerenes C-g, C g, and Cg. A limit for the activation energy of the Stone-Wales transformation J. Am. Chem. Soc. 116 7642-5... 

The possible fatigue failure mechanisms of SWCNT in the composite were also reported (Ren et al., 2004). Possible failure modes mainly include three stages, that is, splitting of SWCNT bundles, kink formation, and subsequent failure in SWCNTs, and the fracture of SWCNT bundles. As shown in Fig. 9.12, for zigzag SWCNT, failure of defect-free tube and tubes with Stone-Wales defect of either A or B mode all resulted in brittle-like, flat fracture surface. A kinetic model for time-dependent fracture of CNTs is also reported (Satapathy et al., 2005). These simulation results are almost consistent with the observed fracture surfaces, which can be reproduced reasonably well, suggesting the possible mechanism should exist in CNT-polymer composites. 

Fig. 9.12 Results of molecular mechanics simulations (a) A Stone-Wales defect (A mode) in a zigzag SWCNT, (b) a Stone-Wales defect (B mode) in a zigzag SWCNT, the bonds with highest potential energy are indicated by arrows. Propagating cracks in (c) A defect-fiee zigzag tube, and (d) defect-lfee armchair tube. Fracture mode of armchair tube with (e) Stone-Wales defect (A mode), and (f) Stone-Wales defect (B mode). Fracture mode of zigzag tube with (g) Stone-Wales defect (A mode), and (h) Stone-Wales defect (B mode) (Huynh et al., 2002. With permission from Wiley)...

In general, differences in chemical bonding and electron configuration between carbon atoms and dopants mandate the deviation from the geometric and electronic equilibrium structure of the aromatic layers in CNTs. As a consequence, topological defects such as Stone-Wales defects are formed with increased probability [37]. 

Fig. 4.4 Molecular model of (a) surface containing positive and negative curvature induced by a pentagon (red) and a heptagon (blue), respectively (b) molecular model of 5-7 defects (yellow) and a Thrower-Stone-Wales defect (green) [82] (c) high-resolution transmission electron microscopy (HRTEM) images of bond rotations V2 (555-777) divacancy, and (d) V2(5555-6-7777) divacancy within graphene scale bar is 1 nm [75].

Stone Wales (1986) considered the ring rearrangement shown in figure 3a. They concluded that as a concerted process it has a Hiickel four-centre transition state and thus will have a substantial activation barrier. The existence of such an activation barrier has been confirmed by the calculations of Yi Bernholc (1992) who found activation energies in excess of 500 kJ mol-1 (5 eV). 

T.C. Dinadayalane, J. Leszczynski, Stone-Wales defects with two different orientations in (5, 5) single-walled carbon nanotubes A theoretical study. Chem. Phys. Lett. 434, 86 (2007)... 

To make investigations more complete we consider also the same fragment of (12,0) CNT with Stone-Wales D0D2a defect [5-7]. 

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... 

Figure 13 The interconversion of pairs of pentagonal and hexagonal rings through the thermally forbidden Stone-Wales transformation...

Restricted Stone-Wales isomerization (i.e. between IPR structures only) has been invoked to explain why relatively few isomers of the higher IPR fidlerenes have been found three of the possible five for C78 have been reported, at least three out of nine for Cg2, and two out of 24 for Cg4. It is postulated that near the carbon arc those isomers which are interconvertable are annealed to the thermodynamically most stable one. At first sight the experimental facts appear to contradict this proposal since all nine of the Cg2 isomers can interconvert, yet at least three isomers have been shown to coexist. It is possible, however, that if these three isomers are of similar energy then a statistical distribution of products would be expected, and this distribution would naturally be dependent upon the temperature at which the Stone-Wales interconversion ceases. As a consequence, whenever a particular fiillerene is isolated the isomer distribution should be reproducible. Results consistent with this idea have indeed been reported for mixtures of the two Stone-Wales interconvertable Cg4 isomers prepared in different laboratories. ... 

Figure 6.24. The potential energy surface of the Stone—Wales transformation before/after the addition of catalyzing moieties such as (a) carbon, and (b) hydrogen atoms. Reproduced with permission from (a) Eggen, B. R. Heggie, M. 1. Jungnickel, G. Latham, C. D. Jones, R. Briddon, R R- Science 1996, 272, 87, Copyright 1996 AAAS and (b) Nimlos, M. R. Filley, J. McKinnon, J. T. J. Phys. Chem. A 2005, 109, 9896. Copyright 2005 American Chemical Society.

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... 

Figure 1.19. The pyracylene or Stone-Wales (SW) rearrangement in Ceo. Top schematic view of the atoms in the SW patch. Bottom pathway calculated with the density-functional tight-binding potential described in the text.

Figure 1.20. A representative monotonic sequence fo the Cgo potential energy surface, showing the energies of minima and the transition states that connect them as a function of the Stone-Wales stack.

Figure 1.21. Disconnectivity graph for minima and transition states in the five lowest Stone-Wales stacks of Ceo- Energy is in hartree relative to the global minimum Buckminsterfullerence structure. The graph including results up to stack seven has the same appearance.

Figure 1.22. The equilibrium occupation probabilities for Stone-Wales stacks up to stack 7 as a function of the total energy relative to Buckminsterfullerene.

Figure 1.23. The occupation probability of Buckminsterfullerene (BF) as a function of energy (relative to the global minimum) and time, starting from an initial uniform distribution in Stone-Wales stack 7. The curves represent times (from left to right) of 3000, 2000, 1000, 500, 100, 1, and 0.1 ps.

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