CLOSS DIRADICAL - SOME SURPRISES ON THE POTENTIAL-ENERGY HYPERSURFACE

The singlet and triplet potential energy surfaces for 1,3-cyclopentanediyl (Closs's diradical) have been investigated using ab initio electronic structure theory. The triplet C2v structure previously postulated to be an intermediate in the ring inversion of bicyclo[2.1.0]pentane (BCP) is found to correspond to a saddle point, rather than a minimum, on a potential energy surface more complex than that originally proposed by Closs. The singlet and triplet surfaces share several qualitative features, but the triplet stationary points lie approximately 1 kcal/mol below the corresponding singlets. The BCP ground state and the singlet and triplet stationary points for Closs's diradical have been fully optimized using a DZ + d basis set at the SCF and CISD levels of theory.