Calculations on 1,8-naphthoquinone predict that the ground state of this diradical is a singlet.

(12/12)CASPT2, (16/14)CASPT2, B3LYP, and CCSD(T) calculations have been carried out on 1,8-Naphthoquinone (1,8-NQ), to predict the low-lying electronic states and their relative energies in this non-Kekule quinone diradical. CASPT2 predicts a (1)A(1) ground state, with three other electronic states-B-3(2), B-3(1), and B-1(1)-within about 10 kcal/mol of the ground state in energy. On the basis of the results of these calculations, it is predicted that NIPES experiments on 1,8-NQ(center dot-) will find that 1,8-NQ is a diradical with a singlet ground state. (C) 2018 Wiley Periodicals, Inc.