Diatomic carbon
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| Names | |
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IUPAC name
Diatomic carbon
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Systematic IUPAC name
Ethenediylidene (substitutive)
Dicarbon(C—C) (additive) |
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| Identifiers | |
12070-15-4 
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| 3D model (Jmol) | Interactive image |
| ChEBI | CHEBI:30083 |
| ChemSpider |
122807 
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| 196 | |
| PubChem | 139247 |
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| Properties | |
| C2 | |
| Molar mass | 24.02 g·mol−1 |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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| Infobox references | |
Diatomic carbon (systematically named ethenediylidene and dicarbon(C—C)), also called dicarbon, is an inorganic chemical with the chemical formula C=C (also written [C
2] or C
2). It is a gas that only exists above 3,642 °C (6,588 °F)), below which it aggregates into graphite or fullerenes. It occurs in carbon vapor, for example in electric arcs; in comets, stellar atmospheres and the interstellar medium; and in blue hydrocarbon flames.
Dicarbon is the preferred IUPAC name. The systematic names ethenediylidene and dicarbon(C—C), valid IUPAC names, are constructed according to the substitutive and additive nomenclatures, respectively.
Ethenediylidene is viewed as ethylene with four hydrogen atoms removed. By default, this name pays no regard to the electronic state of the diatomic carbon. When the electronic state is considered, the states with no unpaired electrons are named ethenediylidene, whereas the states with two unpaired electrons are named ethenediyldiylidene, and the states with four unpaired electrons are named ethenetetrayl.
Molecular orbital theory shows that there are two sets of paired electrons in a degenerate pi bonding set of orbitals. This gives a bond order of 2, meaning that there should exist a double bond between the two carbons in a C2 molecule. However, a recent paper by S. Shaik has suggested that a quadruple bond exists in diatomic carbon, a conclusion that was opposed by J. Grunenberg.
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