Topic
Hydrogen atom abstraction
About: Hydrogen atom abstraction is a research topic. Over the lifetime, 7059 publications have been published within this topic receiving 151781 citations.
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TL;DR: In this paper, the reaction between H2O2 and two water oxidation catalysts was studied by means of in situ 1D and 2D-NMR experiments in order to elucidate if catalyst degradation proceeds through the initial functionalization of a quaternary carbon atom (C-attack) or by hydrogen abstraction of the Cp* -C-CH3 moiety.
Abstract: The reaction between H2O2 and two water oxidation catalysts {[Cp*Ir(H2O)3](NO3)2 (1, Cp* = pentamethylcyclopentadienyl) and [Cp*Ir(bzpy)(NO3)] (2, bzpy = 2-benzoylpyridine)} was studied by means of in situ 1D- and 2D-NMR experiments in order to elucidate if catalyst degradation proceeds through the initial functionalization of a quaternary carbon atom (C-attack) or by hydrogen abstraction (H-attack) of the Cp* –C–CH3 moiety. It was shown that 1 underwent double functionalization of the –C–CH3 moiety of Cp* leading to the formation of –C(OR)–CH2OR (R = H or OH) in a strictly analogous manner to that previously observed for the reaction of 1 with Ce4+. On the contrary, two new intermediates associated with the oxidative degradation of 2, which are functionalized only at the quaternary carbon atom(s) of the –C–CH3 moiety [–C(OR)–CH3], were intercepted and characterized by NMR spectroscopy. This indicates that the oxidative degradation of water oxidation catalysts, featuring the –Cp* ancillary ligand, likely starts with preferential C-attack.
79 citations
79 citations
TL;DR: In this article, the rate constants of triplet quenching are derived and the pathways of deactivation for triplet acetone in solution are discussed, as well as the quantum yields of acetone disappearance.
Abstract: Kinetic studies of the absorption and emission of triplet acetone and the absorption of the ketyl radical, following flash excitation of acetone in a variety of solvents, are reported as well as the quantum yields of acetone disappearance.Rate constants of triplet quenching are derived and the pathways of deactivation of triplet acetone in solution are discussed.
78 citations
TL;DR: In this article, the authors review experimental and theoretical investigations of excited-state hydrogen atom transfer (ESHAT) reactions along unidirectionally hydrogen bonded solvent "wire" clusters and show that the reaction proceeds by H-atom transfer along the wire as a series of Grotthus-type translocation steps.
Abstract: We review experimental and theoretical investigations of excited-state hydrogen atom transfer (ESHAT) reactions along unidirectionally hydrogen bonded solvent ‘wire’ clusters. The solvent wire is attached to the aromatic ‘scaffold’ molecule 7-hydroxyquinoline (7HQ), which offers an O–H and an N hydrogen bonding site, spaced far enough apart to form two- to four-membered wires. S 1 ← S 0 photoexcitation renders the O–H group more acidic and the quinolinic N more basic. This provides a driving force for the enol → keto tautomerization, probed by the characteristic fluorescence of the 7-ketoquinoline in the molecular beam experiments. For 7-hydroxyquinoline·(NH3)3, excitation of ammonia-wire vibrations induces the tautomerization at ∼200 cm−1. Different reaction pathways have been explored by excited-state ab initio calculations. These show that the reaction proceeds by H-atom transfer along the wire as a series of Grotthus-type translocation steps. There is no competition with a mechanism involving success...
78 citations
TL;DR: These two pathways (hydrogen abstraction and oxygen atom transfer) dominate the oxidation reactions catalyzed by these systems, accounting for the moderate oxidizing power and associated selectivity of Mn(Me2EBC)Cl2 in H2O2 oxidations.
Abstract: Distinctive mechanistic pathways account for the remarkable selectivity of a molecularly designed and robust manganese catalyst, Mn(Me2EBC)Cl2, whose activated form has been isolated and thoroughly characterized. In keeping with the existence of two activated catalytic functional groups, MnIV(OH)22+ (BDEOH = 83.0 kcal/mol) and MnIV(O)OH+ (BDEOH = 84.3 kcal/mol), two distinctive Polanyi correlations are observed, the latter being over 10-fold more rapid despite their similarity. Remarkably, only relatively weak C−H bonds (≤∼82 kcal/mol) suffer hydrogen abstraction by either group, with the stoppage occurring at substrate BDECH ≥ catalyst BDEOH. Earlier studies established a selective Lewis acid mechanism as the dominant oxygen atom insertion pathway for this catalyst. These two pathways (hydrogen abstraction and oxygen atom transfer) dominate the oxidation reactions catalyzed by these systems, accounting for the moderate oxidizing power and associated selectivity of Mn(Me2EBC)Cl2 in H2O2 oxidations.
78 citations