Hydrogenation labeled

Figure 5-3. Active site and calculated PES properties for the reactions studied, with the transferring hydrogen labelled as Hp (a) hydride transfer in LADH, (b) proton transfer in MADH and (c) hydrogen atom transfer in SLO-1. (i) potential energy, (ii) vibrationally adiabatic potential energy, (iii) RTE at 300K and (iv) total reaction path curvature. Reproduced with permission from reference [81]. Copyright Elsevier 2002...

In mechanism (8.43) the bridgehead hydrogens of barrelene should be found at the a positions of semibullvalene (2a, 0/3,0y). Mechanism (8.44) can give three different hydrogen-label distributions. If the final bond formation is concerted with bond fission, and bond fission and formation take place at the same carbon atom [mechanism (8.44A)], the label distribution should be (la, 0/3, ly). If bond formation is concerted with bond fission but with a preference for bond formation at the carbon allylic to bond fission [mechanism (8.44B)], the label distribution should be (2a, 0/3, Oy). If there is a symmetric allylic biradical which has a finite existence [mechanism (8.44AB)], then the hydrogen-label distribution should be (1.5a, 0/3,0.5y). 

Can a fortuitous combination of mechanisms (8.43) and (8.44A) account for the observed hydrogen-label distribution in the formation of semi-bullvalene from barrelene If so, how can you eliminate this possibility ... 

The hydrogen-labeled benzobarrelene indicates that the formation of benzo-cyclooctatetraene from the direct photolysis takes place predominantly via benzovinyl bridging<44) j... 

Figure 1. Coordinate system, geometry, and hydrogen labeling scheme, (a) ReHg2 and Hg2 (D h) (b) [ReHs PHo ] (Cs an in the xz plane).

Isotopic Hydrogen Labeling of Heterocyclic Compounds by One-Step Method G. E. Calf and J. L. Garnett, Adv. Heterocycl. Chem., 1973,15, 137-186. 

Isotopic hydrogen labeling of heterocyclic compounds. one-step methods. 15, 137 Isoxazole chemistry, recent developments in. 2, 365 since 1963, 25, 147 lsoxazolidines, chemistry of, 21, 207... 

Isotopic hydrogen labeling of heterocyclic compounds, one-step methods,... 

Palmitate contains 16 carbons, with (14 X 2) + 3 = 31 hydrogens, so each two-carbon unit contains about 4/31 or about 1/8 of the total 3H present. Thus, the counts per minute expected per acetyl-CoA, with two of the four acetyl hydrogens labeled (the other two arising from unlabeled water), is (2/4)(2.48 X 108 cpm//xmol)(l/8) = 1.6 X 107 cpm/jumol, somewhat higher than observed. Exchange between /3-ketoacyl-CoA and solvent water could cause loss of 3H. 

Predict the multiplicities of the absorptions for the hydrogens of these groups. Assume that hydrogens labeled a are different from those labeled x but that all of those labeled... 

A. Garry and S. F. Dyke, Aromat. Heteroaromatic Chem. 1, 66-97 (1973). Isotopic hydrogen labeling of heterocyclic compounds ... 

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