Hindered rotation in xanthenyl-type radicals

Abstract

The e.s.r. spectra of the 9-phenylxanthenyl, 9-phenylthioxanthenyl, and 9-phenylselenoxanthenyl radicals have been interpreted; unambiguous assignments of the hyperfine splitting constants have been made by use of a number of selectively deuteriated derivatives. Although the theoretical models used to interpret the experimental data failed to explain all the details of the spin-density distribution, they allowed certain conclusions to be drawn with respect to the stereochemistry of the molecules.

The results show that the phenyl groups do not rotate freely, but are locked at an angle of ca. 70–80° degrees to the heterocyclic plane.