CryptoCope rearrangement of 1,3-dicyano-5-phenyl-4,4-d(2)-hexa-2,5-diene. Chameleonic or centauric?

The "centauric" model for evaluation of the effect of radical-stabilizing p erturbations on the Cope rearrangement conjectures independent action of su bstituents that make conflicting electronic demands on the two halves of th e transition region. The present test of this conjecture compares 1,3-dicya no-[5-protio]-hexa-1,5-diene (1(H)) and 2-phenylhexa-1,5-diene, with 1,3-di cyano-5-phenylhexa- 1,5-diene (1(Ph)). Thermochemical information required for a proper comparison includes new data of the van't Hoff type on conjuga tive interaction of cyano with the carbon-carbon double bond, reevaluation of the radical-stabilizing potential of the cyano group on secondary and al lyl radicals, comparison with the (reevaluated) stabilizing effect of cyano in "nodal" positions of the Cope transition region, and determination of t he enthalpy and entropy of activation of the cryptoCope rearrangement of ot herwise Cope-incompetent, thermodynamically more stable hexa-2,5-dienes rel ated by prototropy to the Cope-competent hexa-1,5-dienes above. The "chamel eonic" model is concluded to be unsatisfactory, while the "centauric" is in better, if not complete, accord with experiment.