New methods for the regioselective formation of radical anions are described. Dicarboxylates are generated by electrospray ionization mass spectrometry and lose carbon dioxide and an electron upon collision-induced dissociation to afford distonic ions. These radical anions also can be synthesized via laser desorption, chemical ionization, and electron ionization of dibenzyl esters. Subsequent fragmentation of the remaining CO2 affords new radical anions corresponding to neutral reactive intermediates. By measuring the proton affinities and electron binding energies of these species, quantitative energetic information on carbenes, biradicals, and other transient molecules can be obtained. This approach is demonstrated by measuring the heats of formation of 2,3- and 2,6-dehydronaphthalene, ancillary thermochemical data also are derived, and the results are compared to either o- or p-benzyne.