To augment the elucidation of the dependence of enthalpy of stabilization on configuration among the pentadienyl radicals, a designer pentaene of the (Z,Z) type, (R,R)-5,5’,6,6’,7,7’,8, 8’-octahydro-4a,4a’-dimethyl-2,2’-bi-4a(H)-naphrhylidene, has been prepared and subjected to a kinetic study of cis, trans isomerization about its central double bond. The resulting activation parameters and those of a more complicated example, 3,3’-bicholesta-1,4-dienylidene, are essentially identical, their mean values being Delta H-double dagger = 36.8 kcal/mol and Delta S-double dagger = +1.8 eu. This enthalpy of activation is significantly higher than those of pentaenes of the (E,E) and (E,Z) configuration. Conjugative interaction in coplanar cross-conjugated systems of the bis-homofulvalene type not having been experimentally evaluated or estimated by theoretical calculation, an enthalpy of stabilization for the cyclohexadienyl radical is not definitively to be extract-ed at the present lime. if conjugative interactions are to be equated to four Kistiakowsky buradiene units and the difference in steric energies between educt and 90 degrees-twisted state are to be estimated by the MMEVBH program, an enthalpy of stabilization of the cyclohexadienyl radical of similar to 20 kcal/mol results.