Chains of sp-Hybridized Carbon Atoms

Chains of sp-hybridized carbon atoms one-dimensional system 

The reports of Sladkov [36] on a carbon allotrope (carbyne) which would add to the two known carbon hybridization states a third one, namely sp-hybridization in macromolecular chains, were followed by data collected by Whittaker et al. [37] who preferred the name chaoite. 

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Much current research is centering on polyynes—linear carbon chains of sp-hybridized carbon atoms. Polyynes with up to eight triple bonds have been detected in interstellar space, and evidence has been presented for the existence of carbyne, an allotrope of carbon consisting of repeating triple bonds in long chains of indefinite length. 

Cumulenylidene complexes constitute a class of organometallic compounds in which a chain of sp-hybridized carbon atoms is terminated by a sp -hybridized carbon atom (CR2 group) at one end and by a metal-ligand fragment (Lr,M) at the other end. 

Carbynes are supposed to be formed of sp-hybridized carbon atoms bound linearly, where two n electrons have to be involved, giving two possibilities, i.e., an alternative repetition of single and triple bonds (polyyne) and a simple repetition of double bonds (cumulene) (Figure 2.1) [19]. The detailed structure of carbynes is not yet clarified, but some structural models have been proposed [19-22], A structural model is illustrated in Figure 2.11, where some numbers of sp-hybridized carbon atoms form chains that associate together by van der Waals interaction between jr-electron clouds to make layers, and then the layers are stacked. Foreign atoms are intercalated between the layers that are supposed to stabilize the carbyne structure. In the carbyne family, the variety of structures seems to be mainly due to the number of carbon atoms forming a linear chain, in other words, to the layer thickness, and to the density of chains in a layer. 

The flexibility of an individual chain of an elastomer depends on the structure of the intervening unit of sp -hybridized carbon atoms. Some rotation can occur around the O bonds. The... 

The results demonstrated that both compression and shear can induce the formation of C-C bonds between sp-hybridized carbons atoms, which leads to polymerization within the SAM. Interestingly, it was found that the location of these reactive sites within the film could influence the calculated friction. For instance, if the diacetylene components in the chains were close to the tip/film interface, reactions between the film and tip could occur, which led to wear and high friction. On the other hand, if the diacetylene moieties were far from the tip, the reactions did not lead to wear and had little effect on the average calculated friction. These observations demonstrate that a proper treatment of the chemical reactivity of the system may be necessary in some cases to calculate friction accurately. 

In the 1H noise-decoupled 75.5 MHz 13C NMR spectrum of 72, the signals of the sp-hybridized carbon atoms C15 and C. 15 are found at 98.3 and 97.3 ppm. This is in the expected region for substituted alkynes and the chemical shifts agree very well with those of other didehydrocarotenoids. As can be seen in Table 21, the 15,15 -triple bond leads to an upheld shift of ca 22 ppm for the directly connected C14 and C. 14. The chemical shifts of the other carbon atoms of the polyene chain are also affected a downheld shift is observed for the odd carbon atoms and a (shght) upheld shift for the even carbon atoms, both decreasing with increasing distance from the central part. 

Linear carbon chains with variable crystal lattice parameters could be obtained. The carbon film is composed of a mixture of spb and sp-hybridized carbon atoms. Therefore we are dealing with carbynoid structures. Carbynoid crystals of 1 pm size were obtained. 

Decreasing the ratio acetylene/oxygen from T=1.15tor=l.l causes a decrease in the content of sp-carbon atoms in the films but increases the chain length of sp-hybridized carbon. 

It has been generally accepted that polyacetylene has a planar structure, irrespective of cis and trans forms, due to ir-conjugation between the sp hybridized carbon atoms in the polymer chain [1,4]. If it were possible to modify such a planar structure of pofyacetylene into a hehcal one [13], one might expect novel magnetic and optical properties [14]. Here, we report polymerization of acetylene in asymmetric reaction field constructed with chiral nematic LCs, and show that pofyacetylene films formed by helical chains and fibrils can be synthesized [15]. Polymerization mechanism giving hehcal structure from primary to higher order and hierarchical spiral morphology is discussed. 

It has been generally accepted that PA has a planar structure, irrespective of cis and irans forms. This is due to 7i-conjugation between the sp -hybridized carbon atoms in the polymer chain. If it were possible to modify this planar structure of PA into a helical one, novel magnetic and optical properties might... 

Assume for the purposes of this problem that to be an alcohol (-0I) or an amine (-amine), the hydroxyl or amino group must be bonded to a tetrahedral sp hybridized) carbon atom. Write the structural formula of a compound with an unbranched chain of four carbon atoms that is an ... 

Alkyl groups bonded to the sp -hybridized carbon atoms of alkenes affect the stability of the double bond. The chemical reactivity of alkenes also is often affected by the number of alkyl groups bonded to the sp -hybridized carbon atoms. Thus, it is useful to classify alkenes by the number of alkyl groups attached to the C=C structural unit. This feature is called the degree of substitution. An alkene that has a single alkyl group attached to the sp -hybridized carbon atom of the double bond is monosub-stituted. An alkene whose double bond is at the end of a chain of carbon atoms is also sometimes called a terminal alkene. Alkenes that have two, three, and four alkyl groups bonded to the carbon atoms of the double bond are disubstituted, trisubstituted, and tetrasubstituted, respectively. 

The classes of alkynes are more limited than the classes of alkenes because only one alkyl group can bond to each sp-hybridized carbon atom of the triple bond. If one alkyl group is bonded to one of the carbon atoms of the triple bond, the compound is a monosubstituted albyAe (R—C=C—H). This is also called a terniinal alhyne because the triple bond is at the end of the carbon chain. When alkyl groups are bonded to both carbon atoms of the triple bond, the compound is a disubstituted, or an intemal alkyne (R—C=C—R). 

The polymer is an elastomer. The sp -hybridized carbon atoms between double bonds provide some flexibility to the elastomer. However, the trans arrangement of the double bond, which resembles that of gutta-percha, allows chains to pack efficiently and leads to less flexibility in the elastomer. 

As discussed above, amorphous carbon consists of graphite crystallites and amorphous areas. In amorphous areas, there are micropores, sp -hybridized carbon atoms, and carbon chains, some of which also form part of large graphene molecules. Aroimd the micropores, some defects such as free carbon radicals may be foimd. Micropores are regarded as "reservoirs" for lithium... 

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