Peripheral carbon atoms

The conclusion from this observation is that the acidic groups are bound only to the peripheral carbon atoms of each layer, as had been expected. 

It is remarkable that the oxygen content exceeded the number of peripheral carbon atoms significantly. Hennig thought it likely that part of the oxygen was bound in between the carbon layers forming ether links between adjacent layers which are puckered at the periphery. 

Further substitution of the peripheral carbon atoms of the cyclazines by heteroatoms (N, S, etc.) is indicated in this chapter according to the replacement nomenclature system (aza, thia, etc.). Although, strictly, this runs contrary to the rules,lc since it is a heterocyclic, not a hydrocarbon, system which is replaced, the connection between closely related compounds can more clearly be seen. It should be noted that Chemical Abstracts employs the systematic fusion nomenclature I, for instance, is pyrrolo[2,l,5-cd]indolizine. 

Cyclazinium salts with an odd number of peripheral carbon atoms do not rank among the class of cyclazines in the narrow sense. 

Iley and Riley (36) have prepared graphite by cracking hydrocarbons in the presence of a fused silica support at 800° to 1300° C. Both moist and dry preparations at 1000° to 1200° C. contain from 0.5 to 1% hydrogen. They propose that these hydrogen atoms are on peripheral carbon atoms and probably inhibit crystal growth. 

Bernstein et al. have used IR spectroscopy and mass spectrometry to study the products formed from photochemical transformation of naphthalene, anthracene, chrysene, phenanthrene, pyrene, tetracene, pentacene, perylene, benzo(e)pyrene, benzo(ghi)perylene, and coronene in water ices using ultraviolet radiation under astrophysical conditions [27]. The results of their investigation have revealed that peripheral carbon atoms can be oxidized to produce aromatic alcohols, ketones, ethers (when bay region is present,... 

The electron-transfer mechanism supposes that the unpaired electrons in the G -band of a transition metal will pair up with tt electrons of the graphite in contact with the metal. As a result, the number of mobile n electrons in the graphite decreases. This, in turn, will weaken the average strength of the bonds between peripheral carbon atoms and carbon-oxygen complexes that are intermediates in the gasification process. Hence, the liberation of these to the gas phase will be facilitated and gasification enhanced. 

Figure 28.3. Titanasiloxane frameworks for clarity, the peripheral carbon atoms of the substituents at silicon are omitted.

It is interesting to find nitrogen among the products evolved from graphite, for its presence as a stable compound in the lattice may mean that it replaces carbon atoms in the edges of graphite laminae, or is firmly attached to peripheral carbon atoms in the laminae. 

The most important pyrrole derivatives are macrocyclic rings with four pyrrole molecules, known as porphyrins. There are numerous groups, such as methyl, vinyl or acetic acid, attached to the peripheral carbon atoms. In the center - between the... 

Positional corrections (in- and out-of-plane movements) were also permitted for peripheral carbon atoms on rings II and IV of both dimer halves (see fig. 1). The positions of these atoms are particularly crucial for the hfc s of non-methyl /5-protons (two bonds away from the T-system) ... 

The presence of an external heteroatom on a PAH is sufficient to breack the symmetry of the isolated PAH, as discussed by Liu et al. [193] who evidenced some pseudo- Jahn-Teller effects on the ground and electronic excited states in metal-benzene complexes. Concerning structures of PAH and heteroatom, there is a competition between absorption sites on top of a carbon, on top of the middle of a C-C bond or on top of the center of an aromatic cycle. The most stable structure results from the competition between a stronger interaction with a single carbon atom in the first case and smaller but multiple interactions with 6 carbon atoms in the last case. For instance, the cycle center site is prefered for (Fe-PAH) complexes [201] while the site on top of a carbon atom is favoured in (Si-PAH) complexes [183]. In the latter structure, peripheral carbon atoms usually present better... 

Placing the chlorine atom on any of the peripheral carbon atoms will lead to the same compound ... 

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