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 article, two successive processes result in photoproduct generation, one quenching, independent of macroscopic viscosity, and is not simply reflected in the observed quantum yield, the second process involves separation of two caged radicals, and does not occur in rigid media.
73 citations
73 citations
TL;DR: The ideal catalyst for such a process should be able to activate a readily available, nontoxic terminal reductant to form the transition-metal hydride, act as a radical-generating agent, and reduce the radical through HAT.
Abstract: Radical reduction by HAT (hydrogen atom transfer) is an essential step in numerous radical reactions. While transition-metal hydrides are in principle excellent reagents for this purpose because of their low bond dissociation energies, their use in such reactions is attractive only when they serve as catalysts. The ideal catalyst for such a process should be able to activate a readily available, nontoxic terminal reductant to form the transition-metal hydride, act as a radical-generating agent, and reduce the radical through HAT. A system matching the requirements is the reductive epoxide opening catalyzed by [Cp2TiH] (1; Scheme 1).
73 citations
TL;DR: In this paper, the diffusion coefficients of the BP kethyl radical and BP in various solvents, including 2-propanol and acetoaldehyde, were obtained simultaneously, and only the signals due to intermediate radicals were observed.
Abstract: The transient grating method is used for investigating the diffusion dynamics of the transient radicals created by photoinduced hydrogen abstraction reactions of benzophenone (BP) in various solvents, acetone in 2-propanol, and acetoaldehyde in ethanol. The diffusion coefficients (D) of the BP kethyl radical and BP are obtained simultaneously. In acetone/2-propanol and acetoaldehyde/ethanol systems, only the signals due to intermediate radicals are observed. The D values of the transient radicals are two to three times smaller than those of BP
73 citations
TL;DR: The rate data indicate that a direct hydrogen abstraction process dominates for triplet acetone, while a charge-transfer mechanism, namely, exciplex-induced quenching, becomes important for singlet-excited acetone.
Abstract: The fluorescence and phosphorescence quenching of acetone by 13 aliphatic amines has been investigated. The bimolecular rate constants lie in the range of 108−109 M-1 s-1 for singlet-excited acetone and 106−108 M-1 s-1 for the triplet case. The rate data indicate that a direct hydrogen abstraction process dominates for triplet acetone, while a charge-transfer mechanism, namely, exciplex-induced quenching, becomes important for singlet-excited acetone. Pronounced stereoelectronic effects toward H abstraction, e.g., for 1,4-diazabicyclo[2.2.2]octane (DABCO), and significant steric hindrance effects, e.g., for N,N-diisopropyl-3-pentylamine, are observed. A negative activation energy (Ea = −0.9 ± 0.2 kcal mol-1 for triethylamine and DABCO) and the absence of a significant solvent effect on the fluorescence quenching of acetone are indicative of the involvement of exciplexes. Full electron transfer can be ruled out on the basis of the low reduction potential of acetone, which was found to lie below −3.0 V vers...
73 citations