ORTHO-BENZYNE, META-BENZYNE, AND PARA-BENZYNE - A COMPARATIVE CCSD(T) INVESTIGATION

Geometries and energies of ortho-benzyne (1), meta-benzyne (2), and para-benzyne (3) have been calculated at the CCSD(T), GVB, GVB-LSDC, and MBPT(2) levels of theory employing the 6-31G(d, p) basis. Calculations suggest relative energies of O, 13.7, and 25.3 kcal/mol, respectively, and Delta H-f(o) (298) values of 110.8, 123.9, and 135.7 kcal/mol for 1, 2, and 3. With the Delta H-f(o) (298) value of 3, the reaction enthalpy 6RH(298) and the activation enthalpy Delta H-#(298) for the Bergman cyclization of (Z)-hexa-1,5-diyn-3-ene to 3 are calculated to be 9.1 and 28.5 kcal/mol.