Pyranyl Radicals and Their Dimers

Article abstract of DOI:10.1246/bcsj.62.2279

Photochemical and chemical reduction of pyrylium salts in THF solution gave their corresponding radicals which were in equilibrium with dimers.The quantum yields for radical formation and the standard enthalpy change ΔH₀ for dimerization decrease with increasing the electron-donating character of the substituting groups in the pyrylium ring.Specially ΔH₀ for pentaphenylpyranyl and pentaphenylthiopyranyl radicals, in which all carbons in the ring are substituted by phenyl groups, become possitive.The absorption maxima and their extinction coefficients of pyranyl radicals, and concurrently the equilibrium constants for the dimerization were determined spectrophotomerically.