Hydrogen replacement

Two types of hydrogen replacement are discussed here (1) the base-induced hydrogen-deuterium exchange reactions and (2) the hydrogen-metal exchange reactions. 

Other limitations of electrochemical fluorination ate that compounds such as ethers and esters ate decomposed by hydrogen fluoride and cannot be effectively processed. Branching and cross-linking often take place as a side reaction in the electrochemical fluorination process. The reaction is also somewhat slow because the organic reactant materials have to diffuse within 0.3 nm of the surface of the electrode and remain there long enough to have all hydrogen replaced with fluorine. The activated fluoride is only active within 0.3 nm of the surface of the electrode. 

What are the three products resulting from free-radical chlorination of toluene Why are only three hydrogens replaced ... 

Starches can have a hydrogen replaced by something else, such as a carboxymethyl group, making carboxymethyl starch. 

Reactions in which hydrogen replaces another leaving group ... 

Benzene with five hydrogens replaced are pentasubstituted, and when all six hydrogens are replaced, the benzene is hexasubstituted. 

All the known annulenones are either polyenynones (dehydroannulenones), often with fused cyclohexene rings, or have pairs of internal hydrogens replaced by monatomic bridges. They will be discussed in order of increasing ring size. 

Once more, replacement of the hydroxyl hydrogen by a group or an atom more electronegative than hydrogen, replacement of the hydroxyl oxygen by its third period counterpart, or, a combination thereof, will enhance n—a interaction and should lead to a preference for the crowded W conformation over the Y con-. formation. This expectation is confirmed by ab initio calculations in which the preferred conformation for NH2OF is found to be the more crowded W con-former314. ... 

A mesoionic compound PR-G-138-C1 (XXXIX) from Pharma Research in Canada is reported to lower blood pressure in man at low doses by a vasodilator type mechanism (43). This structure is related to SIN-10 (XL) which was reported earlier by Japanese scientists as active in dogs (44). Compounds related to structure XXXIX were compared in spontaneous hypertensive rats and those with the oxadiazole ring hydrogen replaced by chlorine or bromine were as active as the parent compound, although replacement by methyl caused a loss of activity (45). 

The hydrogen economy is a vision for a future in which hydrogen replaces fossil fuels. Economically, the wasteful hydrogen process translates to electricity from hydrogen and fuel cells costing at least four times as much as electricity from the grid. In fact, electricity would be much more efficiently used if it were sent directly to the apphances instead. The transition to a hydrogen economy would require a... 

The hydrogen economy is a vision for a future in which hydrogen replaces fossil fuels. Economically, the wasteful hydrogen process translates to electricity from... 

Astatohalobenzenes can be synthesized directly in At recoil (Table III) experiments either via hydrogen replacement by recoil astatine in monohalobenzenes or by halogen replacement in dihalo-benzenes. In the former, total yields range from 5 to 15%, with an almost statistical mixture of ortho-, meta, and para-astatohalobenzene products 145, 150). The production of AtC5H4F from the corresponding CIC6H4F isomers has been achieved with yields of 14% without noticeable isomerization of the products (19). 

The magnitude of current and substrate feed rate determine the degree of hydrogen replacement per pass, typically 20 - 50 % per pass, but partially fluorinated materials may be recycled to give higher fluorinated products. 

Of course this need not necessarily be the case, as in any mechanism where species are attached to an anode, changes in their electronic make-up, resulting from hydrogen replacement by fluorine, might be expected to cause variations in the adsorption forces with possible desorption into the electrolyte as a consequence. 

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