OBSERVATION OF THE ONSET OF THE INPLANE ROTATION OF PERINAPHTHYL (PHENALENYL, PERINAPHTHENYL) IN THE SOLID-STATE BY EPR AND ENDOR

The onset of the in-plane rotation of perinaphthyl in polycrystalline perinaphthenone tosylhydrazone and perinaphthene (phenalene) has been observed in preliminary EPR and ENDOR experiments. The temperature range over which the spectra exhibit the transition from the stationary state of the molecule to the rotating form is 210-220 K (in perinaphthenone tosylhydrazone) and 205-210 K (in perinaphthene). The EPR proton hyperfine and proton ENDOR powder spectra of stationary perinaphthyl below the transition range have been simulated with g∥ (out-of-plane), g⊥ (in-plane) equal to 2.00278, 2.00226, respectively, principal hyperfine constants, Axxp, Ayyp, Azzp equal to 5.05(±0.30), 7.16(±0.30), 2.95(±0.35) MHz, respectively and Axxm, Ayym, Azzm equal to -8.84(±0.30), -26.04(±0.30), -17.68 (±0.25) MHz, respectively. (p and m refer to protons at ring positions para, meta, respectively, to the central C atom of the molecule.) Spectra above the transition range have been simulated with the same g and out-of-plane A∥ = Azz values and average in-plane values A⊥ = (Axx + Ayy)/2. The following observations provide evidence for the existence of the in-plane rotation of the perinaphthyl molecule above the transition range: (a) The principal values of Am below the transition range equal the corresponding values of the protons of the terminal CH groups of the glutaconic acid radical scaled down to the spin density, pm = 0.28 on the meta C of perinaphthyl, as indicated by the solution spectrum. (b) The Ap principal values below the transition range likewise scale to the glutaconic acid radical values for the central {A figure is presented} group (with pp = -0.08). (c) The in-plane principal Am and Ap values observed below the transition range become averaged above the range, while the out-of-plane values remain unchanged. © 1990.