[2+1] Cycloaddition of Ketene Radical Cation and Ethylene

The reaction of the ketene radical cation and neutral ethylene has been investigated by using tandem mass spectrometry and Fourier transform mass spectrometry. The reaction was conducted at high pressures (150–500 mtorr) in the presence of an inert bath gas which permitted collisional stabilization and isolation of the adduct for study by collisionally activated dissociation (CAD) and metastable ion spectroscopy. The structure of the adduct was established to be that of the cyclobutanone radical cation. Thus, the mechanism of the reaction is a facile [2+1] cycloaddition across the carbon-carbon double bond of the ketene radical cation.