α,2-, α,3-, and α,4-dehydrophenol radical anions:: Formation, reactivity, and energetics leading to the heats of formation of α,2-, α,3-, and α,4-oxocyclohexadienylidene

We have regiospecifically generated the alpha,2-, alpha,3-, and alpha,4-dehydrophenoxide anions by collisional activation of o-, m-, and p-nitrobenzoate. The alpha,2 and alpha,4 isomers also were synthesized by reacting o-benzyne radical anion with carbon dioxide and electron ionization of p-diazophenol. All three dehydrophenol radical anions were differentiated from each other and identified by probing their chemical reactivity with several reagents. Each isomer was converted to phenoxide and its corresponding quinone as well. Thermochemical measurements were carried out on all three radical anions and their hydrogen-atom affinities, proton affinities, and electron binding energies are reported. These measured quantities are combined in thermodynamic cycles to derive the heats of formation of each of the radical anions and their corresponding carbenes (i.e., alpha,2-, alpha,3-, and alpha,4-dehydrophenol). These results are compared to MCQDPT2, G3, G2+(MP2), and B3LYP calculations and experimental data for appropriate reference compounds.