Gas-phase reactions of the dichlorocarbene radical cation

Abstract

The gaseous dichlorocarbene radical cation is reported to behave as a highly reactive electrophile rather than a radical toward various organic substrates in a Fourier-transform ion cyclotron resonance mass spectrometer. For example, the carbene ion reacts with alkyl halides (R–X) via fast electrophilic addition to form a covalently bonded, internally excited intermediate Cl₂C–X–R⁺˙. The intermediate fragments either homolytically or heterolytically to produce net halogen atom or halide ion transfer products, respectively. The observed ionic reaction product is determined by the ionization energies of the two possible neutral fragments (CCl₂X˙ and R˙). The fragment with the lower ionization energy preferentially retains the charge. Most reactions observed for heteroatom-containing organic compounds also appear to follow this electrophilic addition–elimination mechanism. In some cases, addition of carbonyl compounds to the carbene ion is followed by homolytic cleavage of the C–O bond to yield a new carbene radical cation.