4985-62-0Relevant articles and documents
Lunde,Hentz
, p. 863 (1967)
Deactivation of the first excited singlet state of thiophenols
Riyad, Yasser M.,Naumov, Sergej,Hermann, Ralf,Brede, Ortwin
, p. 1697 - 1706 (2006)
On the bases of picosecond and nanosecond laser flash photolysis with detection by emission and absorption spectroscopy, a quantitative description is given of all deactivation channels of the first excited singlet state of thiophenols ArSH(S1) such as fluorescence, intersystem crossing (ISC), chemical dissociation into radicals, and radiation-less internal conversion (IC). For this purpose, the photolysis of thiophenol and its methyl-, methoxy-, and chloro-substituted derivatives was studied in solvents of increasing polarity: 1-chlorobutane, ethanol, and acetonitrile. The fluorescence lifetime of the thiophenols was found to range from some hundreds of picoseconds up to a few nanoseconds, correlating with fluorescence quantum yields between 0.001-0.040, at room temperature. Depending on the substitution pattern of the aromatic ring, the quantum yield of the S-H bond dissociation was found to be between 0.3-0.5, irrespective of the solvent polarity. In laser photolysis, no triplet formation of the investigated compounds could be observed neither by the direct way nor by subsequent sensitization with β-carotene. As a difference to the total, the radiation-less internal conversion (ΦIC ≥ 0.5) was found to be the dominating process. the Owner Societies 2006.
Kinetic studies of retinol addition radicals
El-Agamey, Ali,Fukuzumi, Shunichi,Naqvi, K. Razi,McGarvey, David J.
, p. 1459 - 1465 (2011)
Retinol neutral radicals (RS-retinol), generated from the reaction of retinol with 4-pyridylthiyl and 2-pyridylthiyl radicals in argon-saturated methanol, undergo β-elimination, which can be monitored via the slow secondary absorption rise at 380 nm attributed to the rearrangement of the unstable retinol neutral addition radicals to the more stable addition radicals. Rate constants for the β-elimination reactions (kβ) of 4-PyrS-retinol were measured at different temperatures and the Arrhenius equation for the reaction is described by log (kβ/s -1) = (12.7 ± 0.2) - (54.3 ± 1.3)/, where = 2.3RT kJ mol-1. The reactivities of retinol addition radicals (RS-retinol), generated from the reaction of retinol with various thiyl radicals, towards oxygen have also been investigated in methanol. In the presence of oxygen, the decay of RS-retinol fits to biexponential kinetics and both observed rate constants for the RS-retinol decay are oxygen-concentration dependent. This suggests that at least two thiyl addition radicals, formed from the reaction of RS with retinol, undergo oxygen addition reactions. In light of the estimated rate constants for oxygen addition to RS-retinol and RS-CAR (CAR: carotenoid), the antioxidant-prooxidant properties of retinol are discussed. The Royal Society of Chemistry 2011.
Understanding Chemoselectivity in Proton-Coupled Electron Transfer: A Kinetic Study of Amide and Thiol Activation
Qiu, Guanqi,Knowles, Robert R.
supporting information, p. 16574 - 16578 (2019/10/21)
While the mechanistic understanding of proton-coupled electron transfer (PCET) has advanced significantly, few reports have sought to elucidate the factors that control chemoselectivity in these reactions. Here we present a kinetic study that provides a quantitative basis for understanding the chemoselectivity in competitive PCET activations of amides and thiols relevant to catalytic olefin hydroamidation reactions. These results demonstrate how the interplay between PCET rate constants, hydrogen-bonding equilibria, and rate-driving force relationships jointly determine PCET chemoselectivity under a given set of conditions. In turn, these findings predict reactivity trends in a model hydroamidation reaction, rationalize the selective activation of amide N-H bonds in the presence of much weaker thiol S-H bonds, and deliver strategies to improve the efficiencies of PCET reactions employing thiol co-catalysts.
Control of intramolecular orbital alignment in the photodissociation of thiophenol: Conformational manipulation by chemical substitution
Lim, Jeong Sik,Lee, Yoon Sup,Kim, Sang Kyu
, p. 1853 - 1856 (2008/12/22)
(Graph Presented) Intramolecular orbital alignment can be controlled by conformational tuning of the initial wavepacket location on the two-dimensional potential-energy surfaces of thiophenol (see picture; CI = conical intersection). Chemical substitution induces conformational preference, leading to a dramatic change of the branching ratio between X and A states of the phenylthiyl radical.
