Directed Gas-Phase Synthesis of Triafulvene under Single-Collision Conditions.

The triafulvene molecule (c-C4 H4 )-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 (CH3 CCH) and allene (H2 CCCH2 ) 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 C3 H4 isomer followed by unimolecular decomposition through elimination of atomic hydrogen from the CH3 or CH2 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).