Structure Elucidation of Polyene Systems with Extensive Charge DelocalizationCarbocations from Allylic Carotenols

The structures of two diastereomeric cations, readily prepared from β,β-caroten-4-ol (1) by treatment with trifluoroacetic acid, have been determined by NIR and NMR spectroscopy, resulting in the complete structure elucidation of the most extensively delocalized carbocations so far described. Higher partial charge was observed toward the center of the polyene chain (larger filled red circles). Bond reversion occurs in the central region of the molecule.