Zwitterionic and canonical isomers of a novel quinonoid species were studied using second-order Moller-Plesset perturbation theory with 6-31+G**+5(sp)4d basis sets. An experimental report on the zwitterion being the most stable isomer was confirmed. In particular, the zwitterionic isomer is lower than the lowest canonical tautomer by 1.42 kcal/ mol. Binding an electron to all isomers studied was considered, and the corresponding anionic species were studied. The lowest neutral isomer (zwitterion) forms a stable dipole-bound anion as do three out of four canonical isomers. However, the electron binding energy estimated for the zwitterion (521 cm(-1)) is the largest among all tautomers. (C) 2002 Elsevier Science B.V. All rights reserved.