Benzene with molecular deuterium

Thus, evidence has accumulated in support of hydrogen exchange in benzene by a mechanism involving associatively chemisorbed benzene, and without the necessity to postulate the participation of chemisorbed C Hs. One attractive test of these ideas which, so far as we know, has not been made, would be to repeat, for example, the reaction of para-xylene with deuterium using as catalyst a palladium thimble. This system would allow the exchange reaction to proceed either in the presence of molecular deuterium (both reactants on same side of the thimble) or in the presence of atomic deuterium only (xylene and molecular deuterium on opposite sides of the thimble, so that the hydrocarbon reacts only with chemisorbed atomic deuterium that arrives at the surface after diffusion through the metal). 

Deuterium NMR is used to study the molecular mobility of benzene-de in Na and Cs forms of zeolite X. The systems studied were prepared with loadings in the range 0.7 molecules/supercage to 5.6 and 5.0 mole-cules/supercage for (Na)X and (Cs,Na)X, respectively. 

Figure 3.2.4 The effect of motion about the molecular symmetry axis, either by two-fold orn-fold (n>3) flips, on the deuterium spectrum of a deuter-ated para-substituted benzene. Reproduced with permission from Ref. [10].

Carbon-13 NMR has been used to study anisotropic rotational motion in liquids, as have combinations of techniques. Gillen and Griffiths (1972) have obtained the two reorientational relaxation times for benzene (a symmetric top) by combining reorientation relaxation times obtained from Raman band shapes and deuterium spin-lattice NMR relaxation times. The most extensive series of measurements probing anisotropic molecular reorientations have been made by Pecora and co-workers (Alms et al., (1973a, b)), who combined Carbon-13 spin lattice relaxation times with those obtained from depolarized Rayleigh spectra. 

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