It has been shown that thermolysis of naphthocyclopropane 8 yields the singlet 1, 8- naphthoquinodimethane 7 by disrotatory ring opening. In fluid solution the singlet biradical prefers to ring close to regenerate the starting material rather than under a 1, 2-hydrogen shift to yield phenalene (9). It has been demonstrated that the singlet 7 does not react with O2 or undergo intersystem crossing to ground state triplet 7. It has also been shown by an ...