Carbon subnitride or dicyanoacetylene (C₄N₂) is a compound of carbon and nitrogen. It has a linear structure, NCCCCN, with alternating triple and single covalent bonds. In other words, it is acetylene with the two hydrogen atoms replaced by cyanide groups.

At room temperature, carbon subnitride is a clear liquid. Because of its high endothermic heat of formation, it can explode to carbon powder and nitrogen gas, and it burns in oxygen with a bright blue-white flame at a temperature of 5260 K (4987 °C, 9008 °F), which is the hottest flame of any chemical, according to Guinness World Records.

As a reagent in organic chemistry

Dicyanoacetylene is a powerful dienophile because the cyanide groups are electron-withdrawing, so it is a useful reagent for Diels-Alder reactions with unreactive dienes. It even adds to the aromatic compound durene (1,2,4,5-tetramethylbenzene) to form a substituted bicyclooctatriene. Only the most reactive of dienophiles can attack aromatic dienes.

In outer space

Solid dicyanoacetylene has been detected in Titan's atmosphere by infrared spectroscopy. As the seasons change on Titan, the C₄N₂ condenses and evaporates in a cycle, which allows scientists on Earth to discover things about Titanian meteorology.

As of 2006, the detection of dicyanoacetylene in the interstellar medium has been impossible, because its symmetry means it has no rotational microwave spectrum. However, similar asymmetric molecules like cyanoacetylene have been observed, and it is suspected that advances in astronomical infrared spectroscopy will lead to the detection of interstellar C₄N₂.

References

Inorganic carbon compounds | Nitrides