6119-32-0Relevant articles and documents
Tris(trimethylsilyl)silane (TTMSS)-derived radical reactivity toward alkenes: A combined quantum mechanical and laser flash photolysis study
Lalevee, Jacques,Allonas, Xavier,Fouassier, Jean Pierre
, p. 6434 - 6439 (2007)
(Figure Presented) The reactivity of the tris(trimethylsilyl)silane (TTMSS)-derived radical is studied through an approach combining laser flash photolysis and quantum mechanical calculations. The results obtained for TTMSS are compared both to a classica
Direct Irradiation of Phenol and Para-Substituted Phenols with a Laser Pulse (266 nm) in Homogeneous and Micro-heterogeneous Media. A Time-Resolved Spectroscopy Study
Siano, Gastón,Crespi, Stefano,Bonesi, Sergio M.
, p. 14012 - 14025 (2020/11/20)
Direct irradiation of para-substituted phenols under N2 atmosphere in homogeneous (cyclohexane, acetonitrile, and methanol) and micellar (SDS) solution was investigated by means of time-resolved spectroscopy. After a laser pulse (266 nm), two transient species were formed, viz. the para-substituted phenol radical-cations and the corresponding phenoxy radicals. The radical-cations showed a broad absorption band located between 390 and 460 nm, while the phenoxy radicals showed two characteristic bands centered at 320 nm and 400-410 nm. The deprotonation rate constant of radical-cations (kH) of 105 s-1 and the reaction rate constant of the phenoxy radicals (kR) in the order of 109-1010 M-1·s-1 have been derived. The kH rate constants gave good linear Hammett correlation with positive slope indicating that electron-withdrawing substituents enhance the radical-cation acidity. The binding constants (Kb) of the para-substituted phenols with the surfactant were also measured, and NOESY experiments showed that phenols were located in the hydrophobic core of the micelle. Finally, computational calculations provided the predicted absorption spectra of the transients and nice linear correlations were obtained between the theoretical and experimental energy of the lower absorption band of these species.
The effect of the medium polarity on the mechanism of the reaction of hydroxybenzenes with hydrazyl radical in aprotic solvents
Belaya,Belyj,Zarechnaya,Scherbakov,Mikhalchuk,Doroshkevich
, p. 690 - 697 (2017/05/29)
Mechanisms of the reaction of di- and trihydroxybenzenes with 2,2′-diphenyl-1-picrylhydrazyl (stable radical) in aprotic media of different polarity have been elucidated by experimental and quantum-chemical methods. Kinetic, stoichiometric, and activation
Structural and medium effects on the reactions of the cumyloxyl radical with intramolecular hydrogen bonded phenols. the interplay between hydrogen-bonding and acid-base interactions on the hydrogen atom transfer reactivity and selectivity
Salamone, Michela,Amorati, Riccardo,Menichetti, Stefano,Viglianisi, Caterina,Bietti, Massimo
supporting information, p. 6196 - 6205 (2014/07/21)
A time-resolved kinetic study on the reactions of the cumyloxyl radical (CumO?) with intramolecularly hydrogen bonded 2-(1-piperidinylmethyl)phenol (1) and 4-methoxy-2-(1-piperidinylmethyl)phenol (2) and with 4-methoxy-3-(1-piperidinylmethyl)phenol (3) has been carried out. In acetonitrile, intramolecular hydrogen bonding protects the phenolic O-H of 1 and 2 from attack by CumO? and hydrogen atom transfer (HAT) exclusively occurs from the C-H bonds that are α to the piperidine nitrogen (α-C-H bonds). With 3 HAT from both the phenolic O-H and the α-C-H bonds is observed. In the presence of TFA or Mg(ClO 4)2, protonation or Mg2+ complexation of the piperidine nitrogen removes the intramolecular hydrogen bond in 1 and 2 and strongly deactivates the α-C-H bonds of the three substrates. Under these conditions, HAT to CumO? exclusively occurs from the phenolic O-H group of 1-3. These results clearly show that in these systems the interplay between intramolecular hydrogen bonding and Br?nsted and Lewis acid-base interactions can drastically influence both the HAT reactivity and selectivity. The possible implications of these findings are discussed in the framework of the important role played by tyrosyl radicals in biological systems.
Laser flash photolysis study of the reactivity of β-naphthoflavone triplet: Hydrogen abstraction and singlet oxygen generation
De Lucas, Nanci C.,Santos, Guilherme L.C.,Gaspar, Caio S.,Garden, Simon J.,Netto-Ferreira, José Carlos
, p. 121 - 129 (2015/02/19)
The absorption spectra for β-naphthoflavone (1) reveal a solvatochromic red shift in polar solvents which is consistent with the π,π? character of the S0 → S1 electronic transition. The laser flash photolysis technique has been used to characterize and study the reactivity of the triplet excited state of 1. Excitation (355 nm) of degassed solutions of 1, in acetonitrile, resulted in the formation of its corresponding triplet excited state. Addition of hydrogen donors, such as 2-propanol and 1,4-cyclohexadiene, led to triplet quenching and formation of a new transient, which was assigned to the corresponding ketyl radical obtained from a hydrogen abstraction reaction by triplet 1. This ketyl radical was characterized by experiments with methylviologen. The triplet excited state of 1 was efficiently quenched by phenols and N-acetyl l-tryptophan methyl ester. In all cases new transients were formed in the quenching process, which were assigned to the corresponding radical pair resulting from an initial electron transfer from the quencher to the excited naphthoflavone, followed by a fast proton transfer. Singlet oxygen (1O2) is formed from the triplet of 1, and a quantum yield of 0.51 was measured. TDDFT calculations with implicit solvation (IEF-PCM) were used to calculate the ground state UV-vis absorption spectrum, from which the nature of the lowest energy transitions were characterized, and the triplet-triplet absorption spectrum consistent with the triplet transient generated by LFP. Excellent correlation of the calculated and experimental spectra was achieved using the conventional PBE0 hybrid functional.
Hydrogen hyperfine splitting constants for phenoxyl radicals by DFT methods: Regression analysis unravels hydrogen bonding effects
Amorati, Riccardo,Pedulli, Gian Franco,Guerra, Maurizio
body text, p. 3136 - 3141 (2010/08/21)
DFT calculations using the B3LYP functional, medium-sized basis sets and empirical scaling of the results provide quantitative estimates of the hydrogen isotropic hyperfine splitting constants (hscs) in 2,6-di-alkyl phenoxyl radicals (1-11). Literature hs
A laser flash photolysis and theoretical study of hydrogen abstraction from phenols by triplet α-naphthoflavone
De Lucas, Nanci C.,Fraga, Helena S.,Cardoso, Cristiane P.,Correa, Rodrigo J.,Garden, Simon J.,Netto-Ferreira
experimental part, p. 10746 - 10753 (2011/05/19)
The hydrogen abstraction (HA) reaction by the triplet of α-naphthoflavone (1) has been investigated experimentally by the use of laser flash photolysis (LFP) and theoretically with density functional theory (DFT) and atoms in molecules (AIM). The triplet
Phenolic hydrogen abstraction by the triplet excited state of thiochromanone: A laser flash photolysis study
Ribeiro, Alessandra M.,Bertoti, Ada Ruth,Netto-Ferreira, Jose? Carlos
scheme or table, p. 1071 - 1076 (2010/10/21)
Triplet ketones are known to oxidize biological substrates which can lead to damage of several biomolecules such as amino acids, nucleosides and DNA. As part of our systematic study on the interaction between carbonyl compounds and phenols, the triplet reactivity of thiochromanone (1) towards substituted phenols, in acetonitrile, was investigated employing the laser fash photolysis technique. The quenching rate constants ranged from (1.1 ± 0.1) × 108 L mol-1 s-1 (4-cyanophenol) to (5.8 ± 1.0) × 109 L mol-1 s-1 (hydroquinone). A Hammett plot for the reaction of triplet 1 with phenols containing polar substituents resulted in a reaction constant ρ =-0.90. This negative value observed for the reaction constant ρ is in accord with a mechanism in which the hydrogen transfer from phenols to the triplet carbonyl involves a coupled electron/proton transfer.
Laser flash photolysis study of the photochemistry of thioxanthone in organic solvents
Rodrigues, Janaina F.,De Assis Da Silva, Francisco,Netto-Ferreira, Jose? Carlos
scheme or table, p. 960 - 965 (2010/10/21)
The photoreactivity of the triplet excited state of thioxanthone (TX) was investigated employing the laser fash photolysis technique. The wavelength for the absorption maximum and the lifetime of the triplet excited state are solvent dependent. When hydrogen donor solvents were employed, a new band at 410 nm was observed in the triplet absorption spectrum, which was attributed to the ketyl radical derived from thioxantone. Quenching rate constants, kq, ranged from (1.7 0.1) × 106 L mol-1 s-1 for toluene to ca. 109 L mol-1 s-1 for phenol and its derivatives containing polar substituents, as well as for indole, triethylamine and DABCO.
Unexpected acid catalysis in reactions of peroxyl radicals with phenols**
Valgimigli, Luca,Amorati, Riccardo,Petrucci, Silvia,Pedulli, Gian Franco,Hu, Di,Hanthorn, Jason J.,Pratt, Derek A.
supporting information; experimental part, p. 8348 - 8351 (2010/02/28)
Weak organic acids in millimolar concentrations increase the reactivity of peroxyl radicals with common phenolic antioxidants dramatically. This counterintuitive phenomenon relies on a substantially different reaction mechanism from that in the absence of an acid: rate-determining electron transfer occurs from the hydrogen-bonded phenol to the hydroperoxide cation radical present in equilibrium with the peroxyl radical under these conditions (see scheme).
