Computational Study of Deprotonation of Cyclopropa-Fused Quinones

The acidities of cyclopropa-fused quinones 1H–3H were calculated by employing MP2 and B3LYP methods utilizing the 6-31+G(d) basis set. Analysis of the results shows that all three isomers are considerably more acidic than the previously studied cyclopropabenzene. It is also shown that acidity of1His significantly higher than acidity of 2H and 3H. The acidity ordering of the studied species is rationalized by a triadic formula, which is capable of delineating the initial, intermediate and the final state effects in the deprotonation process. It is found that the ordering of the calculated proton affinities is mainly determined by an interplay of two terms: Koopmans’ionization energy and the relaxation energy.