Cel The proton dynamics in a number of solid heterocycles have been investigated. For hydrogen-1 fast magnetic field cycling nuclear magnetic resonance (NMR) spectroscopy experiments, a special field cycling spectrometer was constructed. The X-ray crystal structure was examined for evidence of disorder in the N-H to N hydrogen bonding between the molecules, some of which form discrete n-mers (n = 2,3,4); selected examples were then enriched with nitrogen-15 and studied by nitrogen-15 (and in some cases carbon-13) cross polarization - magic angle spinning (CP-MAS) NMR spectroscopy. From changes in the appearance of the spectra with temperature, the presence of dynamic disorder could be inferred and the proton jump times measured. A smaller number of compounds were then studied by high speed MAS magnetization transfer and the frequency dispersion of the hydrogen-1 spin lattice relaxation time. Deuterated samples with a wide range of enrichment were also investigated in order to study the kinetic isotope effect as a function of temperature. A wealth of new information has been obtained on electronic structure and mechanisms of proton transfer in the solid state. There is some evidence for a change in the transfer mechanism between the dimer of 3,5-diphenyl-4-bromo-pyrazole and the trimer of 3,5-dimethylpyrazole, in which the double and triple proton jumps, respectively, are believed to be concerted, and the tetramers of 3,5-phenyl-methyl-pyrazole and 3,5-diphenylpyrazole, in which there is some theoretical evidence for a stepwise mechanism. It has been shown that in the trimer of 3,5-dimethyl-pyrazole, the rate constant departs very significantly from an Arrhenius dependence at low temperatures, due, it is believed, to the existence of proton tunnelling as a major reaction pathway, for which the kinetic isotope effect is providing further evidence. Studies of nitrogen-15 chemical shift anisotropy and intermolecular proton transfer in host guest crystals and on surfaces have also been performed. Experiments to measure the N-H distance in several N-H to N hydrogen bonds have recently shown great promise.Proton exchange and tunnelling in a number of crystals containing N-H...N N-H...O and O-H...O hydrogen bonds will be studied by a combination of the techniques of CPMAS NMR spectroscopy and quadrupole resonance and relaxation, so as to cover the widest possible range of exchange lifetimes. Additionnal studies will be carried out on molecules embedded in disordered organic glasses and other host materials. X-ray crystal structure determinations combined with LCAO-MO calculations on molecular aggregates will also be undertaken in an effort to correlate the dynamic, thermodynamic and structural factors. Dziedzina nauki engineering and technologymaterials engineeringcrystalsnatural sciencesphysical sciencesopticsspectroscopyabsorption spectroscopy Program(-y) FP2-SCIENCE - Programme plan (EEC) to stimulate the international cooperation and interchange needed by European research scientists (SCIENCE), 1988-1992 Temat(-y) Data not available Zaproszenie do składania wniosków Data not available System finansowania CSC - Cost-sharing contracts Koordynator KING'S COLLEGE LONDON Wkład UE Brak danych Adres STRAND WC2R 2LS LONDON Zjednoczone Królestwo Zobacz na mapie Koszt całkowity Brak danych Uczestnicy (2) Sortuj alfabetycznie Sortuj według wkładu UE Rozwiń wszystko Zwiń wszystko ALBERT-LUDWIGS-UNIVERSITAET FREIBURG Niemcy Wkład UE Brak danych Adres Fahnenbergplatz 79085 FREIBURG (IN BREISGAU) Zobacz na mapie Koszt całkowity Brak danych CONSEJO SUPERIOR DE INVESTIGACIONES CIENTIFICAS Hiszpania Wkład UE Brak danych Adres Calle Serrano 117 MADRID Zobacz na mapie Linki Strona internetowa Opens in new window Koszt całkowity Brak danych
