Hydrogen exchange reaction restricted rotation

In order to establish this supposition of a restricted rotation around the coordination bond, it should be assured that the contribution of the dissociation mechanism is negligibly small in the hydrogen-exchange reaction. For this purpose, a 1 1 mixture of (ZJ-propene-l-rf, (composition d0, 3.6% Z-l-dlt 86.1 % E-l-, 7.5% Z-l, 2-d2,1.4% E-l,2-d2,0% and 1, l-d2,1.4%) and propene-d6 (purity, propene-powder catalyst at room temperature, and HD gas (98 %) was added as a cocatalyst. In this experiment, the amounts of Mo—H and Mo—D sites are approximately equal during reaction. The primarily exchanged products formed by associative and dissociative mechanisms are described respectively in Scheme 11. 

N-Nitroso compounds have been found to exist as syn and anti rotamers [30, 31] due to restricted rotation of the N-N bond resulting from nitrogen lone-pair delocalization (Fig. 3.2). This delocalization causes the hydrogens at the a-carbons to become acidic as evident by their base-catalyzed reactions, such as exchange with deuterium... 

In equation (23), a and a2 are the molecular radii of the reactants and r the internuclear separation between them. For a self-exchange reaction where there is no change in coordination number, ai a2 = a, and if it is assumed that electron transfer occurs between the reactants in close contact, a1 + a2 = r which leads to equation (24). Equations (23) and (24) neglect specific contributions from individual solvent molecules such as hydrogen bonding and, also, possible dielectric saturation effects that may arise because of restricted rotations of solvent dipoles in the near vicinity of the electrostatic fields of the ions. 

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