Hydrogen-donating group

CgH COO from BPO. The first type involves direct radical displacement on the oxygen—oxygen bond and is the preferred mode for nucleophilic radicals, eg, -CH(R)OR7 The second type involves radical addition to, or abstraction from, the hydrocarbyl group adjacent to the peroxide this is the preferred mode for electrophilic radicals, eg, Cl C (eq. 32). In the last type (eq. 33), there is hydrogen donation from certain hydrogen-donating radicals, eg, ketyls (52,187,188,199). 

A recently discovered variant of the Wallach technique is the silver ion cata lyzed fluorination of aryl diazo sulfides in hydrogen fluonde-pyridine-toluene solvent [57] (equation 12) Electron withdrawing substituents such as acetyl give higher yields of aryl fluoride (71%) than electron donating groups (butyl 39%, methoxy, 2-14%), reductive dediazoniation competes with fluorination... 

Due to the two electron-donating groups in the bicyclic product 150 and the unhydrolyzed precursor of 148, they should be quite reactive dienes in Diels-Alder reactions. However, such [4+2] cycloadditions were observed only for the cyclohexane-annelated cyclopentadienes 151b, which equilibrate with the more reactive isomers 154 by 1,5-hydrogen shifts (Scheme 33). The [4+2] cycload-... 

Phenyl or mixed alkyl/phenyl substituted silicon hydrides show similar reactivities to trialkylsilanes. Indeed, by replacing one alkyl by a phenyl group the effect on the hydrogen donating ability of SiH moiety increases only slightly. ... 

Hydrogen bonding between Br2 and 2-substituted phenols having electron-donating group is strong enough to orf/io-brominate these phenols. Therefore, o/t/io-bromination of phenol, o-cresol and 2-allylphenol was promoted by only NBS without amines. 

Ketimines were hydrogenated faster than aldimines, and electron-donating groups accelerated the rate of hydrogenation. The OH and RuH bonds are regenerated by hydrogen transfer to the unsaturated 16-electron Ru complex from isopropanol, generating acetone (Scheme 7.13). 

The products of such reactions can be useful intermediates in the synthesis of commercial drugs. The nature of the substituents within the benzophenones has an effect on rate, with electron-withdrawing groups favoring the reaction more than electron-donating groups. For example, kinetic studies showed that p-trifluoromethylbenzophenone was hydrogenated 11-fold faster than the p-... 

Electron-donating groups (amino, methylamino, hydroxy, methoxy) in the 2-position, on the other hand, are extremely undesirable because, unlike similar substituents in the 1,4-positions, they are unable to form intramolecular hydrogen bonds with the keto groups of anthraquinone and hence are highly susceptible to photo-oxidation [167]. 

---