STABILITIES OF TRIVALENT CARBON SPECIES .5. EQUILIBRIA OF EXCITED SINGLET ALCOHOLS AND CARBOCATIONS

Fluorescence titrations were carried out with four alcohols whose greatly enhanced reactivity to form carbocations in the excited singlet state is predicted by Forster cycle calculations. Analysis of the fluorescence titration of 5H-dibenzo[a, d]cycloheptatrien-5-ol indicates that the alcohol reacts with acid in the excited singlet state, but not the ground state, at HR between +1 and -3. Formation of the cation at very low acid concentrations, as predicted by the Forster cycle, is precluded by the short lifetime of the excited singlet alcohol. The behavior of the fluorescence intensities of the alcohol and corresponding cation implies the involvement of another, nonfluorescing species in the excited-state reactions. Preparative photolyses of the cation indicate that its principal photoreactions are hydride transfer and ether formation. © 1979, American Chemical Society. All rights reserved.