Etude des Mouvements Moléculaires dans li Cyclohexane Plastique à l'Aide d'une Sonde Radicalaire par Résonance Paramagnétique Electronique et Double Résonance Electronique Nucléaire

Evidence concerning the formation of a heterogeneous solid solution in the plastic phase of cyclohexane doped with a nitroxide free radical from magnetic resonance studies

“…With this, and the assumption that the spin-diffusion regime was rapid, as suggested by the DNP results [10], a value for the critical radius 3 could be deduced. The striking result was that its value, which cannot be smaller than the average distance between the electronic spin and the first neighbouring cyclohexane protons (averaged over a time not smaller than (reABe)-lg4 x 10 .8 s, much longer than the rotational correlation time [9] r a ~ 10-9-10 -1~ s), is found to be ~ 1.7 A, much smaller than expected ( ~ 6.3 A) from steric considerations. At that time no explanation was found for this result.…”

“…The aim of the present paper is to reconsider the DNP and SLR data of references [9][10][11] in the light of the new results of references [13][14][15]. This new analysis will essentially lead to the conclusions labelled (i) and (ii).…”

“…In previous papers, magnetic resonance studies of the plastic phase of cyclohexane doped with the nitroxide free radicals TANO and TANANE have been reported [9][10][11][12][13][14][15]. In this system, in addition to E.P.R.…”

“…It is currently used in biology [6] and in the field of liquid crystals [7,8], but it has been seldom used for the study of plastic crystals. In plastic cyclohexane [9][10][11][12][13][14][15], camphene [16], camphor [17], using suitable free radicals at low concentrations, the E.P.R. lines are found to be narrow, suggesting (i) that the radicals are diluted in the medium and (ii) that the motion is sufficiently rapid, two features which show that spin labelling may be an interesting method for studying these systems.…”

“…In this system, in addition to E.P.R. at both X and Q bands [9], dynamic nuclear polarization (DNP) [10][11][12][13], nuclear spin lattice relaxation via the radicals (SLR) [10][11] and electron-electron double resonance(ELDOR) [14,15], experiments have been performed. However, so far there is no picture which can explain consistently all these results.…”