Carbon sheets aromaticity

So long as the proportion of carbon atoms involved in bonds with fluorine rmains small— in C4F it is one quarter—the aromatic character of graphite with plane carbon sheets is retained. Bonding of fluorine, however, certainly produces tension within the layers and this may be the reason for the low thermal stability. The carbon planes become puckered when, as in carbon monofluoride, the majority of the carbon atoms become involved in sp bonds. The fact that no further compound occurs in the region between CF0.28 (= Cs.eF) and CFo.es and that there is no continuous transition from the one compound to the other is in keeping with this view. For the monofluoride the most stable preparations are those which approximate most closely to CFi.o, as the puckered carbon planes are then free of strain. The further the composition deviates from the ideal formula the greater is the strain, as is shown by the observed increase in thermal instability with decreasing fluorine content. 

Structural Parameters. Average structural parameters include aromaticity (fa), degree of substitution of the aromatic sheet(a), number of carbon atoms per alkyl substituent (n), ratio of peripheral carbons per aromatic sheet to total aromatic carbons (Haru/Car) and aliphatic H/C ratio can be calculated according to Eq. (1)-(5)... 

Figure 2. Proposed mechanism for carbonization of cyclicized PAN fiber into aromatic carbon sheets. (Reprinted with permission from Ref. 22. Copyright 1975 Elsevier).

Fig. 4.12 The structural relationship between graphene sheet and single-walled carbon nanotube arrows point to two alternative directions of rolling circles inside rings reflect on aromatic character of carbon rings and delocalization of resonant electrons inside them...

Graphite is perhaps the simplest layered structure. The intralayer C—C distance (142 pm) is twice the covalent radius of aromatic carbon (cf. 139 pm in benzene) and the Interlayer C—C distance is 335 pm, twice the van dcr Wools radius of carbon. The sheets are held together by weak van der Waals forces. Many substances can be... 

Fig. 6. Model of asphaltene structure (wavy lines represent the zigzag configuration of a saturated carbon chain or a loose net of naphthenic rings and straight lines represent the edge of flat sheets of condensed aromatic rings) (Yen et at., 1961).

Graphite, which is one of the allotropes in carbon, has unique features characterized by two-dimensionality and amphoteric nature. This is based on the 2D layered structure with the Ji-electronic structure extended in the constituent graphene sheets. The electronic structure of graphene, which is described in terms of the extrapolation of condensed polycyclic aromatic molecules to infinite size,... 

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