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Carbon Compounds
Carbon has the ability to form very long chains of interconnecting
C-C bonds. This property is called catenation.
Carbon-carbon bonds are strong, and stable. This property allows carbon to form an almost infinite number of compounds; in fact, there are more known carbon-containing compounds than all the compounds of the other chemical elements combined except those of hydrogen (because almost all organic compounds contain hydrogen too).
The simplest form of an organic molecule is the hydrocarbon—a large family of organic molecules that are composed of hydrogen atoms bonded to a chain of carbon atoms.
Chain length, side chains and functional groups all affect the properties of organic molecules. By
IUPAC's definition, all the other organic compounds are functionalized compounds of hydrocarbons.[citation needed]
Carbon occurs in all known organic life and is the basis of organic chemistry. When united with hydrogen, it forms various flammable compounds called hydrocarbons which are important to industry as refrigerants, lubricants, solvents, as chemical feedstock for the manufacture of plastics and petrochemicals and as fossil fuels.
When combined with oxygen and hydrogen, carbon can form many groups of important biological compounds including sugars, lignans, chitins, alcohols, fats, and aromatic esters, carotenoids and terpenes. With nitrogen it forms alkaloids, and with the addition of sulfur also it forms antibiotics, amino acids, and rubber products. With the addition of phosphorus to these other elements, it forms
DNA and RNA, the chemical-code carriers of life, and adenosine triphosphate (
ATP), the most important energy-transfer molecule in all living cells.
Inorganic compounds
Main article:
Compounds of carbon
Commonly carbon-containing compounds which are associated with minerals or which do not contain hydrogen or fluorine, are treated separately from classical organic compounds; however the definition is not rigid (see reference articles above). Among these are the simple oxides of carbon. The most prominent oxide is carbon dioxide (
CO2). This was once the principal constituent of the paleoatmosphere, but is a minor component of the
Earth's atmosphere today. Dissolved in water, it forms carbonic acid (
H2CO3), but as most compounds with multiple single-bonded oxygens on a single carbon it is unstable. Through this intermediate, though, resonance-stabilized carbonate ions are produced. Some important minerals are carbonates, notably calcite.
Carbon disulfide (
CS2) is similar.
The other common oxide is carbon monoxide (CO). It is formed by incomplete combustion, and is a colorless, odorless gas. The molecules each contain a triple bond and are fairly polar, resulting in a tendency to bind permanently to hemoglobin molecules, displacing oxygen, which has a lower binding affinity.
Cyanide (CN), has a similar structure, but behaves much like a halide ion (pseudohalogen). For example it can form the nitride cyanogen molecule ((CN)2), similar to diatomic halides. Other uncommon oxides are carbon suboxide (
C3O2), the unstable dicarbon monoxide (
C2O),[48][49] carbon trioxide (
CO3), cyclopentanepentone (
C5O5) cyclohexanehexone (
C6O6) [52], and mellitic anhydride (
C12O9).
With reactive metals, such as tungsten, carbon forms either carbides (C4), or acetylides (C2−2) to form alloys with high melting points. These anions are also associated with methane and acetylene, both very weak acids. With an electronegativity of 2.5, carbon prefers to form covalent bonds. A few carbides are covalent lattices, like carborundum (SiC), which resembles diamond.
Organometallic compounds
Main article:
Organometallic chemistry
Organometallic compounds by definition contain at least one carbon-metal bond. A wide range of such compounds exist; major classes include simple alkyl-metal compounds (e.g. tetraethyl lead), η2-alkene compounds (e.g.
Zeise's salt, and η3-allyl compounds (e.g. allylpalladium chloride dimer; metallocenes containing cyclopentadienyl ligands (e.g. ferrocene); and transition metal carbene complexes. Many metal carbonyls exist (e.g. tetracarbonylnickel); some workers consider the carbon monoxide ligand to be purely inorganic, and not organometallic.
While carbon is understood to exclusively form four bonds, an interesting compound containing an octahedral hexacoordinated carbon atom has been reported. The cation of the compound is [(Ph3PAu)6C]2+. This phenomenon has been attributed to the aurophilicity of the gold ligands.
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- published: 05 May 2010
- views: 73990