C3H2

C3H2 is the chemical formula that can describe several hydrocarbon species, of which the best known is cyclopropenylidene (cyclopropen-1-ylidene). This compound is a cyclic carbene with a three‑carbon ring and two hydrogen atoms. The carbon framework features a divalent carbon center, giving cyclopropenylidene its highly reactive character. The three-membered ring and the electronic configuration have made it a subject of interest in carbene chemistry and in discussions of aromaticity in small rings.

In astrochemistry, cyclopropenylidene has been detected in interstellar and circumstellar environments through observations of its rotational transitions. Its presence in cold molecular clouds provides insight into carbon-rich chemistry under low temperatures and densities and helps constrain models of molecular growth in space. The molecule is typically present only in trace amounts and is mostly studied as a reactive intermediate rather than as a stable, isolated species.

C3H2 as a formula can correspond to several structural isomers, but cyclopropenylidene is the most extensively studied. In laboratory settings, cyclopropenylidene is generated transiently by photolysis or pyrolysis of suitable precursors and is often studied by gas-phase spectroscopy or matrix isolation techniques. Its high reactivity as a carbene makes it challenging to isolate, but its spectroscopic signatures enable its identification in both laboratory experiments and space.

Overall, C3H2 serves as a key example of a small, unsaturated hydrocarbon that straddles the line between fundamental carbene chemistry and astrochemical processes.