Hydrogen atom exchange

Rg. 1 27. Nuxnber of hydrogen atoms exchanged against deuterium by dissolution of the sodium salt of the add in D,0 (507). 

Figure 4. Stepwise hydrogen atom exchange between coal and naphthalene. The starting naphthalene was deuterated completely. To simplify the scheme only a- and f -position are shown.

Over some metals, C2H6D is the major initial product, and the amounts of the other deuteroethanes formed decrease steadily with increasing deuterium content. The mean numbers of hydrogen atoms exchanging initially [see Equation (7)] for the metals showing this type of distribution of products are tungsten 1.30, molybdenum 1.16, and tantalum 1.15. 

The symmetry elements of the water molecule are easily detected. There is only one proper axis of symmetry, which is the one that bisects the bond angle and contains the oxygen atom. It is a C2 axis and the associated operation of rotating the molecule about the axis by 180° results in the hydrogen atoms exchanging places with each other. The demonstration of the effectiveness of the operation is sufficient for the diagnosis of the presence of the element. 

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). 

A hydrogen atom exchange between the aromatic ketones completes the equilibrium and leads to an equal amount of the two ketyl radicals. The requirement of the formation of random copolymers Is that the comonomer of lowest triplet energy Is capable of hydrogen abstraction. 

At temperatures of activation of 356° and below, the methyl hydrogen atoms exchange more rapidly than those on the ring. Runs at 215, 244, and 327° gave distribution patterns similar to those shown for 275, 300, and 356°. The amounts of exchange into the ring and into the methyl were determined by NMR (12) since mass spectrographic analysis on... 

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. 

M= multiple exchange factor denoting the average number of hydrogen atoms exchanged within one contact. 

This yield is not significant owing to labile hydrogen atoms exchange with GC columns. 

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