1H, 2H, and 13C ENDOR Studies of Labeled Bis(biphenylenyl)propenyl Type Radicals in Isotropic Solutions and in Liquid Crystals

Article abstract of DOI:10.1021/ja00522a062

Partially deuterated and 13C-labeled bis(biphenylenyl)propenyl radicals have been studied by means of ESR and ENDOR spectroscopy.Isotropic and anisotropic hyperfine contributions could be determined from measurements in isotropic solutions and in nematic and smectic phases of liquid crystals.Assignments of hyperfine coupling constants and shifts to molecular positions were achieved.Conclusions concerning molecular structure, e.g., twist angles, could be drawn by relating the experimental data to quantum mechanical calculations.These results could be confirmed by taking account of the 13C hyperfine shifts determined by ESR and 13C ENDOR experiments.A marked isotope effect on the β-proton hyperfine coupling could be observed when replacing 1H by 2H in the biphenylenyl moieties.The essential feature of the 2H ENDOR measurements in liquid crystals is the detection of deuterium quadrupole splittings.The relaxation behavior of the different magnetic nuclei is discussed.A novel multinuclear ENDOR standard for checking the engineering design of a liquid-phase ENDOR spectrometer is proposed.