User:Jorge Stolfi/Oxocarbon test

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Mellitic anhydride, one of the larger oxocarbons.

An oxocarbon is a chemical compound consisting only of carbon and oxygen.^♦

The simplest and most common oxocarbons are carbon monoxide (CO) and carbon dioxide (CO₂). There are however many other stable or metastable oxides of carbon which rarely occur outside chemical plants and laboratories, such as carbon suboxide (O=C=C=C=O), and mellitic anhydride (C₁₂O₉).^♦

Several new oxides, with various degrees of stability, have been synthesized since the 1990s. These include many oxides which are inherently unstable and can be observed only momentarily as intermediates in chemical reactions. Three important examples are the dicarbon monoxide radical (:C=C=O), carbon trioxide (CO₃),^♦ and 1,2-dioxetanedione (C₂O₄).^♦♦ There are also many oxocarbons which are very reactive, and can be studied only in the gas phase, or under matrix isolation conditions.^♦

Linear carbon dioxides

One family of carbon oxides has the general formula C_nO₂, or O=(C=)_nO --- namely a linear chain of carbon atoms connected by double bonds, capped by oxygen atoms at both ends. The first members are

• CO₂ or O=C=O, the well-known carbon dioxide.
• C₂O₂ or O=C=C=O, the extremely unstable ethylene dione.^♦
• C₃O₂ or O=C=C=C=O, the metastable carbon suboxide or tricarbon dioxide.^♦
• C₄O₂ or O=C=C=C=C=O, tetracarbon dioxide or 1,2,3-Butatriene-1,4-dione.^♦
• C₅O₂ or O=C=C=C=C=C=O, pentacarbon dioxide.^♦

Some higher member of this family (for n = 17,19,21) have been detected in trace amounts in cryogenic matrix experiment ^♦

Radialene-type cyclic polyketones

Cyclopentanepentone, a radialene-type oxocarbon.

Another family of oxocarbons that has attracted special attention are the cyclic radialene-type oxocarbons C_nO_n or (CO)_n.^♦ They can be regarded as cyclic polymers of carbon monoxide, or n-fold ketones of n-carbon cycloalkanes. The first two members are carbon monoxide itself (CO) and the extremely unstable ethylene dione C₂O₂ or O=C=C=O.^♦ Theoretical studies suggest that the next four members — C₃O₃, C₄O₄, C₅O₅, and C₆O₆ — may be stable, but so far they have been synthesized only in trace amounts.^♦

On the other hand, the anions of these oxocarbons are quite stable and have been known since the 19th century.^♦ They are, respectively, deltate (C₃O₃²⁻), squarate (C₄O₄²⁻), croconate (C₅O₅²⁻), and rhodizonate (C₆O₆²⁻). The aromaticity of these anions has been studied using theoretical methods.^♦

New oxides

Many new stable or metastable oxides have been synthesized since the 1990s, such as:

• C₂₄O₆ and C₃₂O₈, respectively cyclic trimer and tetramer of the biradical 3,4-dialkynyl-3-cyclobutene1,2-dione -C≡C-(C₄O₂)-C≡C- (1990)^♦
• C₄O₆, dioxane tetraketone or dimeric oxalic anhydride (1998)^♦
• C₁₂O₆ hexaoxotricyclobutabenzene (2006)^♦♦

Polymeric carbon oxides

Carbon-oxygen polymers of relatively high molecular weight, with 3:2 atomic ratio can be obtained from carbon suboxide (spontaneously)^♦♦ or carbon monoxide (by compression to 5 GPA). ^♦♦ Another carbon-oxygen polymer, with C:O ratio 5:1 or higher, is the classical graphite oxide (1859) ^♦ and its single-sheet version graphene oxide.

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Category:Oxocarbons Category:Carbon compounds Category:Oxygen compounds