carbon

A nonmetallic tetravalent element, atomic no. 6, atomic wt. 12.011; the major bioelement. It has two natural isotopes, ¹²C and ¹³C (the former, set at 12.00000, being the standard for all molecular weights), and two artificial, radioactive isotopes of interest, ¹¹C and ¹⁴C. The element occurs in three pure forms (diamond, graphite, and in the fullerines), in amorphous form (in charcoal, coke, and soot), and in the atmosphere as CO₂. Its compounds are found in all living tissues, and the study of its vast number of compounds constitutes most of organic chemistry. [L. carbo, coal]

- active c. dioxide, activated c. dioxide complex of N-carboxybiotin (biotin + CO₂) and an enzyme; the form in which c. dioxide is added to other molecules in carboxylations; e.g., to methylcrotonyl-CoA to form β-methylglutaconyl in the catabolism of leucine, and to acetyl-CoA to form malonyl-CoA. SEE ALSO: acetyl-CoA carboxylase.

- anomeric c. the reducing c. of a sugar; C-1 of an aldose, C-2 of a 2-ketose.

- c. bisulfide SYN: c. disulfide.

- c. dichloride SYN: tetrachlorethylene.

- c. dioxide CO₂; the product of the combustion of c. with an excess of air; in concentrations not less than 99.0% by volume of CO₂, used as a respiratory stimulant. SYN: carbonic acid gas, carbonic anhydride.

- c. dioxide snow solid c. dioxide used in the treatment of warts, lupus, nevi, and other skin affections, and as a refrigerant. SYN: dry ice.

- c. disulfide an extremely flammable (flashpoint −30°C), colorless, toxic liquid with a characteristic ethereal odor (fetid when impure); it is a parasiticide. SYN: c. bisulfide.

- c. monoxide (CO) a colorless, practically odorless, and poisonous gas formed by the incomplete combustion of c.; its toxic action is due to its strong affinity for hemoglobin, myoglobin, and the cytochromes, reducing oxygen transport and blocking oxygen utilization.

- c. tetrachloride a colorless, mobile liquid having a characteristic ethereal odor resembling that of chloroform; it is used as a cleansing fluid and as a fire extinguisher, and has been used as an anthelmintic, especially against hookworm. SYN: tetrachloromethane.

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car·bon 'kär-bən n, often attrib a nonmetallic element found native (as in diamonds and graphite) or as a constituent of coal, petroleum, asphalt, limestone, and organic compounds or obtained artificially (as in activated charcoal) symbol C see ELEMENT (table)

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car·bon (C) (kahrґbən) [L. carbo charcoal] a nonmetallic tetrad element, found nearly pure in the diamond, and approximately pure in charcoal, graphite, and anthracite; atomic number 6, atomic weight 12.011. The two naturally occurring, stable isotopes are ¹²C (98.89 per cent) and ¹³C (1.11 per cent).