ESR OF ANTHRONYL RADICALS - EVIDENCE OF A TEMPERATURE-DEPENDENT PHENYL TWIST ANGLE IN THE 9-PHENYLANTHRONYL RADICAL

The ESR spectra of three anthronyl radicals are reported; their hyperfine splitting constants, checked by computer simulation, are assigned on the basis of McLachlan and INDO calculations. The 9-phenylanthronyl radical exhibits two particular features: (i) unusual phenyl proton hyperfine splittings, assigned by INDO, (ii) a temperature dependence of the hyperfine splitting constants, tentatively assigned to thermally activated oscillations of the phenyl ring around a locked twisted configuration. The twist phenyl ring angle is estimated on the basis of the decrease of the anthrone proton hyperfine splittings between the unsubstituted and the 9-phenyl substituted radicals rather than directly from the phenyl proton hyperfine splittings. © 1978.