Reactive intermediates via Fourier transform mass spectrometry

A new method for the selective preparation of radical anions in the gas phase is described. Dicarboxylate anions are generated in a Fourier transform mass spectrometer via electrospray ionization, and both carboxylates and an electron are removed to afford odd-electron anions via sequential fragmentations. Energetic measurements on these species enable the heats of formation of neutral compounds to be determined. The heats of hydrogenation of benzocyclobutadiene and acenaphthyne are used to illustrate this methodology and the antiaromaticity and/or strain energy of these molecules are discussed.