Hydrogen atom exchange reactions

The hydrogen atom exchange reactions between Tetralin and diphenylmethane and the reduction of the ketones were studied in the presence of a selected group of raw whole coals, demineralized whole coals, and demineralized macerals. The macerals used in this work were obtained from two hvA bituminous coals, one from the Kentucky Upper Elkhorn No. 3 Seam (PSOC-1103) and one from the Ohio Lower Kittaning No. 5 Seam (PSOC-297) two hvB bituminous coals, one from the Indiana No. 1 Block Seam (PSOC-106) and one from the Hiawatha King 6 Mine and two hvC bituminous coals, one from the Illinois No. 2 Seam and one from the Indiana Brazil Block Seam (PSOC-828). 

Exceptions apart, isotopic exchange in C-H bonds, usually effected in the presence of bases, is sufficiently rapid only if some feature of the molecular structure weakens quite considerably the bond between carbon and hydrogen, i.e.9 renders the hydrogen atom acidic (semilabile hydrogen atom). Exchange reactions of that type are often carried out in order to achieve semilabile labeling, e.g., at the -position of a ketone, the material obtained in this way being later converted into stably labeled compounds by subsequent reactions, e.g., reduction to secondary alcohols. 

Two research groups have investigated the rates of the base-catalyzed hydrogen atom exchange reactions of aliphatic fluorocarbons (3,4,28,29). The results for a selected series of compounds are presented in Table 5. 

The great majority of experimental data (see Section III.A) indicate that the hydrogen-deuterium exchange reaction belongs to the class of acceptor reactions (i.e., reactions that are accelerated by electrons and decelerated by holes). This means that the experimenter, as a rule, remains on the acceptor branch of the thick curve in Fig. 8a, on which the chemisorbed hydrogen and deuterium atoms act as donors. Here a donor impurity must enhance the catalytic activity, while an acceptor impurity must decrease it. This is what actually occurs, as we have already seen (see Section III.A). 

In discussing the mechanism of the para hydrogen conversion or the hydrogen deuterium exchange reaction, Eley (117) suggested that it could occur at a single metal atom. Two orbitals are needed to bind the activated complex and these can be provided easily by the d orbitals of... 

The relative difficulty in alkylating normal paraffins is presumably due to the fact that the exchange reactions of step 1 and step 3 do not take place as easily with hydrogen atoms attached to secondary carbon atoms as with those attached to tertiary carbon atoms (cf. Bartlett, Condon, and Schneider, 15). Under the conditions required to obtain the hydrogen-halogen exchange reaction with normal paraffins, polymerization of the olefin (which may be considered to occur via a reaction similar to that of step 2) takes place very readily and becomes the predominant reaction. 

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