Carbon distinctive features

The chain and branched chain saturated hydrocarbons make up a family called the alkanes. Some saturated hydrocarbons with five carbon atoms are shown in Figure 18-11. The first example, containing no branches, is called normal-pentane or, briefly, n-pentane. The second example has a single branch at the end of the chain. Such a structural type is commonly identified by the prefix iso- . Hence this isomer is called /50-pentane. The third example in Figure 18-11 also contains five carbon atoms but it contains the distinctive feature of a cyclic carbon structure. Such a compound is identified by the prefix cyclo in its name—in the case shown, cyclopentane. 

The most distinctive features of the H and 13C n.m.r. spectra of bicyclic peroxides are provided by their bridgehead nuclei. An analysis of the data on over thirty compounds indicates that the characteristic chemical shift ranges are 5 3.7-4.8 for bridgehead protons and 8 72-89 for bridgehead carbons. 

Some distinctive features of the insertion reactions reported in Table VII can be summarized as follows First, carbon monoxide gives rise by insertion (5, 195a) to acyl bonds which are easily cleaved by water, alcohols, or compounds with mobile hydrogen. The metal is thus easily removed from the organic part and, being eliminated in its reduced state, can undergo a further oxidative addition, leading to a catalytic cycle. Thus, use of CO is very favorable for catalytic reactions. 

Substituents larger than hydrogen atoms cannot generally occupy intraannular positions. We have seen about transannular reactions which are special distinctive feature of medium-sized rings. The transannular reactions do not occur at the carbon atom of the chain and they also do not involve the neighbouring atoms. They take place between atoms on opposite sides of the ring. 

ALHA 84001 is a unique Martian meteorite with an ancient age of 4.5 billion years. It consists mostly of orthopyroxene crystals that accumulated in basaltic magma. Its most distinctive feature, however, is the occurrence of small globules of carbonates with unusual compositions and textures. The controversial (now largely discredited) hypothesis that the carbonates contain evidence of extraterrestrial life (McKay et al., 1996) made this the most famous meteorite on Earth. ALHA 84001 has also experienced intense shock metamorphism. 

Most attention has been devoted to an exploration of the chemistry of the borazaromatics. In these compounds, two neighboring carbon atoms of an aromatic system are replaced by the isoelectronic boron-nitrogen groups as illustrated by the 2,1-borazaronaphthalene, 7 2>3>. Their great chemical stability is a distinct feature of heteroaromatic materials and several reviews of their chemistry have been published 4 6>. 

The distinctive feature of the discussed method for nanostructural carbon material synthesis is that there is a possibility to produce these materials without catalysts owing to a very quick synthesis (competing with velocity of light). An example of such type of process is synthesis of carbon nanotubes by evaporation of pure graphite in liquid media. 

We have carried out tunneling conductance measurements on a large number of N-doped Y-junction carbon nanotubes. The junction (JA) in Fig. 5a exhibits a rectification behavior with distinct change of slope in the I-V data at —1.5 and +1 V. A high value of rectification ratio of 4.75 is obtained for bias voltages of 1.5 V. Coulomb blockade is easily identifiable in the bias range, -0.4 to +0.6 V. The arms of the tube, however, are devoid of blockade but exhibit varied behavior. The arm-1 shows distinct features at 0.4 V. In the case of arm-2, similar... 

A distinctive feature of the H NMR spectra of homotropenylium ion derivatives is that the magnitude of the chemical shift difference (A ) between the S-exo and S-endo proton resonances is found to be dependent on the nature and position of substituents on the seven-membered ring . In all cases, a donor substituent on one of the basal ring carbons attenuates the chemical shift difference. For example, the 1- and 2-hydroxy substituted homotropenylium ions, 16 and 17, have values only some 50-55% of that found for the parent cation Systematic variation in the donor properties of the oxygen substituent using the Lewis acid scale developed by Childs and colleagues led to a linear change in A. ... 

In recent years various new experimental techniques and computerized procedures have become available for the determination and analysis of physisorption data. It is perhaps all the more surprising that some wddely used methods are still based on old and over-simplified principles. This short overview is not intended to provide a critical survey of current research on gas adsorption by carbons and indeed the recent advances in research and development are amply described in the following chapters of this book. However, it is pertinent in this introductory overview to draw attention to some of the major obstacles, which have restricted progress and which now offer the opportunity for further research. The distinctive features of gas/carbon physisorption systems are also briefly compared with the adsorptive behavior of oxides and zeolites. 

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