C3H3

C3H3 is a chemical formula representing several hydrocarbon species with three carbon atoms and three hydrogen atoms. In neutral form, it corresponds to multiple isomers and reactive intermediates, and the formula can also describe charged species such as the cyclopropenyl cation (C3H3+).

Among the best known neutral C3H3 species are the cyclopropenyl radical (a three-membered ring carrying a radical center), the allenyl radical (H2C=C=CH•, a linear cumulated-diene radical), and the propargyl radical (HC≡C–CH2•). These radicals are highly reactive and are studied in combustion chemistry, flame spectroscopy, and astrochemistry.

The chemistry of C3H3 involves various isomers with different bonding, including cyclic and linear arrangements. The cyclopropenyl radical and the allenyl radical illustrate how small hydrocarbon frameworks can host radicals in distinct bonding motifs. The cyclopropenyl cation (C3H3+) is an important aromatic-type cation in theoretical discussions of 2π-electron systems.

Because these species are typically short-lived, they are characterized spectroscopically in low-pressure discharges or high-temperature flames, and predicted by quantum chemical calculations. Their study helps to understand reaction mechanisms in combustion and the formation of larger hydrocarbon networks.

See also: cyclopropenyl radical; propargyl radical; allenyl radical; cyclopropenyl cation.