Carbon-rich, definition

There is no precise definition of an active carbon , but it is generally understood to be a carbonaceous material of appreciable specific surface area. If it is to be an effective adsorbent, an active carbon must have a surface area of at least 5 m2 g1. Active carbons used as industrial adsorbents have much larger BET-areas, which may extend well above 2000 m2 g1. In accordance with this broad definition, an active carbon may be porous or non-porous. The term activated carbon has a more specific connotation, however, since it is reserved for a highly porous carbon produced from a carbon-rich material by some form of chemical or physical activation. 

Observations from studies of surface sediments have allowed definition of regionally varying levels in the ocean at which pronounced changes in the presence or preservation of calcium carbonate result from the depth-dependent increase of dissolution on the seafloor. The first such level to be identified was simply the depth boundary in the ocean separating carbonate-rich sediments above from carbonate-free sediments below. This level is termed the calcite (or carbonate) compensation depth (CCD) and represents the depth at which the rate of carbonate dissolution on the seafloor exactly balances the rate of carbonate supply from the overlying surface waters. Because the supply and dissolution rates of carbonate differ from place to place in the ocean, the depth of the CCD is variable. In the Pacific, the CCD is typically found at depths between about 3500 and 4500 m. In the North Atlantic and parts of the South Atlantic, it is found... 

Many low molecular weight benchmark structures such as adamantane (1), dia-mantane (2) as well as the next several higher diamondoids (3-6), cubane (7), al-lene (8), propyne (9), benzene (10), naphthalene (11), and anthracene (12) (Scheme 8.1) are not all carbon-rich per definition but they serve as excellent models to test the underlying theory and to extrapolate to the much larger carbon-rich, often infinite stmctures. A further distinction can be made according to hybridization, whereby conjugated (sp and sp ) structures are best put in one category and non-... 

In contrast to molecular mechanics force fields, modern semiempirical methods are classified as an SCF electron-structure theory (wavefunction-based) method [12]. Older (pre-HF) semiempirical approaches such as extended Hvickel theory, which can be classified as a one-electron effective Hamiltonian approach, involve drastic approximations but rely on the researcher s intuition and ability to extrapolate from simple computations to meaningful chemistry. This method is not used much these days but still plays a role in determining the band structures of organic polymers, most of which are carbon-rich by definition [13]. 

Redox reactions are better defined in terms of the concept of electron transfer. Thus an atom is said to be oxidized if, as the result of a reaction, it experiences a net loss of electrons and is reduced if it experiences a net gain of electrons. This simple definition can be used to identify oxidation or reduction processes at carbon in terms of a scale of oxidation states for carbon based on the electronegativities of the atoms attached to carbon. The idea is to find out whether in a given reaction carbon becomes more, or less, electron-rich. We will use the following somewhat arbitrary rules ... 

As discussed in the preceding sections of this chapter, the key to living cationic polymerization is to reduce the effect of chain transfer reactions (Scheme 4) because termination is much less important in the cationic polymerization of vinyl monomers. The primary reason for frequent chain transfer reactions of the growing carbocation (1) is the acidity of the /3-H atoms, next to the carbocationic center, where a considerable part of the positive charge is localized. Because of their electron deficiency, the protons can readily be abstracted by monomers, the counteranion (B ), and other basic components of the systems, to induce chain transfer reactions. It is particularly important to note that cationically polymerizable monomers are, by definition, basic or nucleophilic. Namely, they have an electron-rich carbon-carbon double bond that can be effectively poly-... 

Calcite is the dominant cement in all of the sandstones except the chlorite cement-rich Ran-zano. The absence of volumetrically significant cements other than carbonate precludes a definitive placement of carbonate cementation within a progression of diagenetic events. No petrographic evidence marks any particular group of concretions as temporally distinct from another. IGV provides a crude estimate of burial at the time of cementation, and suggests that most of the concretions formed after considerable compaction. 

The definite amount of greenhouse gases in the atmosphere has yet to be calculated. It depends on population, the per capita consumption of fossil fuel, deforestation, forestation activities and countermeasures that balance the extra carbon dioxide in the air. This could include planting more trees. Another factor is the use of alternative energy and conservation. Trades in fuel carbon will also have an effect. Transfers may occur from coal-rich to coal-poor nations. 

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