Hydrogen ordering

The formation of methylcyclopentane from hexanes proceeds in the presence of hydrogen only (27, 27a). A singly dissociated surface intermediate is suggested by the hydrogen order of about — 1 on the right-hand side of the bell-shaped curves over platinum black between 300° and 360°C (Fig. 6) (77). 

Garin and Gault 82) reported a hydrogen order of - 3.4 for position isomerization of n-pentane over alumina-supported platinum between 240° and 300°C. They concluded therefore that a surface species that lost 3-4 hydrogen atoms would cyclize. It is not clear to what extent this discrepancy (cf. 77 and 82) may be attributed to different experimental conditions, to different catalysts, or actually to different mechanisms that is, C5 cyclization with participation of unsaturated intermediates. 

INFLUENCE OF HYDROGEN ORDERING ON THE PROTON SPIN-LATTICE RELAXATION TIME IN LANTHANUM SUPERSTOICHIOMETRIC DIHYDRIDES LaH2+c... 

Keywords Metal hydrides, phase transitions, hydrogen ordering NMR, spin-lattice... 

Ratishvili I.G., Vajda P. "Hydrogen ordering in the superstoichiometric rare-earth dihydrides. The case of a system with an energy constanst ratio p = V2/Vi <1. LaH2+x". Phys.Rev. B (1996), 53, 581-587. 

Ratishvili I.G., Namoradze N.Z. Influence of hydrogen ordering on the spin-lattice relaxation time in metal hydrides I. The high-temperature limit". Bull. Georg. Acad. Sciences. (2004), 169 (2), 279-281. II. The low-temperature limit", ibid, (2004), 169 (3), 481- 483. 

Kuhs WF, Finney JL, Vettier C, Bliss DV (1984) Structure and hydrogen ordering in ices VI, VII and VIII by neutron powder diffraction. J Chem Phys 81 3612-3623... 

K = 410 sec K, Ea = 0.35 eV/atom, x0 - 7.4 x 1011 sec 1. Figure 4b illustrates the role of hydrogen ordering process. There is given delta , the difference in T T) dependences calculated with and without taking into account the ordering effects illustrated by Figs. 2. 

XII (long dashed lines) and extrapolated equilibrium lines at low temperatures (short dashed lines). Hydrogen ordered ices XIII and XIV were prepared by isobaric cooling of HCl (DCl) doped H2O (D2O) ice V or XII to 77 K at 0.5 GPa or 1.2 GPa, respectively (indicated by arrows). Cooling of ice XII w as started at 190 K, which is 10 K below the temperature where transition to stable ice VI would occur. The temperatures of the hydrogen ordering phase transitions are indicated by grey bars. Transition temperatures for ice V ice... 

Here we report the preparation and structures of the two new hydrogen ordered phases of ice named ice XIII and ice XIV. We further show by relative changes of the lattice... 

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