Mass Spectrometry of Benzyne and Cyclopentadienylideneketene

The formation of cyclopentadienylideneketene 2 and benzyne 1 in flash vacuum thermolysis reactions is investigated by on-line mass spectrometry. Compounds 13, 14, and 15 all afford ketene 2, which decomposes to benzyne and CO in the high-temperature regime. Cyclopentadienylideneketene 2 is stable on the microsecond time-scale of neutralization-reionization experiments. Collisional activation mass spectrometry of m/z 76 from 14, 15, and 5 indicates that the C6H4 center dot+ ions most likely undergo ring opening in the mass spectrometer.