ABINITIO CALCULATIONS ON META-QUINONE - THE GROUND-STATE IS A TRIPLET

The geometries of the B-3(2), B-1(2), and 1A1 states of m-quinone (2) have been optimized, using the 6-31G* basis set at, respectively, the UHF, ROHF, and GVB levels. Partial geometry reoptimization was carried out at the pi-SDCI level. Calculations that included sigma,pi correlation also were performed. The triplet is predicted to be the ground state by 10.4 kcal/mol at the pi-SDCI level and by 7.6 kcal/mol at the sigma-S, pi-SDCI level of theory. A value of 9.5 kcal/mol is calculated for the singlet-triplet splitting in m-quinodimethane (1) at the pi-SDCI level. The apparent lack of effect on the singlet-triplet splitting of replacing the CH2 groups in 1 by the oxygens in 2 is discussed.