Hydrogen from water, abstraction

The second point relates to this as well as to your observation that the abstraction of hydrogen from water molecules is assisted by coordination of the water, particularly with Fe+2. The mechanism of ferrous oxidation by hydrogen atom has been a controversial question, and several mechanisms have been proposed. Among them are one suggested by Jortner, Czapski, Stein, and myself involving the addition of hydrogen atoms to the ferrous ion to form a hydrido iron complex analagous to CuH+—i.e.,... 

Dr. Anbar You have to capture it and come up with essentially the same amount of hydrogen. This hydrogen, however, has to come off from the water as can be seen from its composition. This means that no more hydrogen atoms can be formed otherwise, they would abstract hydrogen from the isopropyl alcohol. 

A mechanism which is consistent with the various experimental results for olefin formation involves the initial abstraction of the hydrazone proton (103 - 106)82 In this case, however, expulsion of the tosylate anion is associated with the abstraction of a second hydrogen from C-16 instead of hydride attack on the C=N bond (compare 97 - 98 and 106 - 107). Expulsion of nitrogen from the resulting intermediate (107) yields an anion (108) which is most probably stabilized in the form of a metal complex and can be readily decomposed by water to give an olefin (109). This implies that 17-d1-androst-16-ene (104) can be prepared by using deuterium oxide as the sole deuterated reagent.82... 

Specifically, two p.-aqua-bridges located in the cleft of the dimer have one hydrogen pointing outward from each side, thus allowing the photo-excited p-benzoquinone (labeled in Scheme 8), but not a bulky 2,5-/-Bu-/ -bcnzoquinone, to enter the cleft and abstract a H radical. This mechanism is consistent with the proposed role of the tyrosyl Yz radical as H abstractor from water [165]. The reaction, however, is not catalytic, because of the irreversible formation of hydroquinone. 

The photochemical alkylation of olefins by nitriles and ketones is not straightforward, due mainly to the inefficient abstraction of hydrogen from an electron-withdrawing-substituted carbon by an electrophile such as the photocatalyst excited state. Nevertheless, various methyl ketones have been synthesized by the irradiation of a ketone/oleftn mixture dissolved in aqueous acetone. The mechanism of the reaction remains to be clarified, but a water-assisted C—C coupling between an acetonyl radical and the olefin has been postulated (Scheme 3.12). The reaction has several advantages, as it is cheap (an acetone/water mixture is used as the solvent) and occurs under mild metal-free conditions with no need for a photocatalyst [28],... 

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