ELECTRONIC INTERACTIONS IN ARYNE BIRADICALS - AB-INITIO CALCULATIONS OF THE STRUCTURES, THERMOCHEMICAL PROPERTIES, AND SINGLET-TRIPLET SPLITTINGS OF THE DIDEHYDRONAPHTHALENES

Structural and energetic properties for the lowest energy singlet and triplet states of the 10 didehydronaphthalene isomers are predicted us ing density functional and multireference second-order perturbation th eories. These levels of theory offer excellent agreement with known he ats of formation for three singlet isomers when appropriate isodesmic equations are used for prediction. Singlet-tripler splittings and bira dical stabilization energies are examined to gain insight into the deg ree of interaction between the biradical centers. This interaction ope rates via three distinct mechanisms, namely, through space (overlap), through sigma-bonds, and through pi-bonds, in order of increasing dist ance over which quantitative impact is predicted. The first two effect s are especially sensitive to the relative orientations of the biradic al centers and the shape of the molecular framework that joins them. S impler models are examined for their utility in predicting singlet-tri plet splittings; proton hyperfine splittings in antecedent monoradical s are the best predictors of biradical-state energy splittings.