Directed Gas‐Phase Synthesis of Triafulvene under Single‐Collision Conditions

The triafulvene molecule (c‐C 4 H 4 )—the simplest representative of the fulvene family—has been synthesized for the first time in the gas phase through the reaction of the methylidyne radical (CH) with methylacetylene (CH 3 CCH) and allene (H 2 CCCH 2 ) under single‐collision conditions. The experimental and computational data suggest triafulvene is formed by the barrierless cycloaddition of the methylidyne radical to the π‐electron density of either C 3 H 4 isomer followed by unimolecular decomposition through elimination of atomic hydrogen from the CH 3 or CH 2 groups of the reactants. The dipole moment of triafulvene of 1.90 D suggests that this molecule could represent a critical tracer of microwave‐inactive allene in cold molecular clouds, thus defining constraints on the largely elusive hydrocarbon chemistry in low‐temperature interstellar environments, such as that of the Taurus Molecular Cloud 1 (TMC‐1).