EPR AND ENDOR RELAXATION STUDY OF MOLECULAR MOTIONS OF A KETONE UREA INCLUSION COMPOUND

The radical obtained by gamma irradiation of the 10-nonadecanone/urea inclusion compound has been studied by electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy. The EPR line widths have been analyzed, and the characteristics and the rates of the molecular motions of the included molecule have been obtained in the temperature range 160-290 K. Two different types of motion have been detected: the wobbling motion of the methylene groups about the carbon-carbon bond modulates the beta proton isotropic hyperfine interactions, while overall uniaxial rotation inside the host channel mainly modulates the anisotropic dipolar interaction of the alpha proton. The internal motion is faster and has higher activation energy than molecular rotation. These results have been confirmed by the analysis of the amplitudes of the ENDOR lines of the gamma and zeta protons, which shows that the internal motion rate is just in the range of the electron spin Larmor frequency, while the rotation rate is lower.