2122-46-5Relevant articles and documents
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
, p. 1071 - 1076 (2010)
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.
Pathways and kinetic energy disposal in the photodissociation of nitrobenzene
Galloway, Douglas B.,Bartz, Jeffrey A.,Huey, L. Gregory,Crim, F. Fleming
, p. 2107 - 2114 (1993)
Vacuum-ultraviolet photoionization molecular-beam mass spectrometry is a means of identifying primary photodissociation products and determining their recoil energies.At several photolysis wavelengths between 220 and 320 nm, we have observed three primary photodissociation pathways for nitrobenzene.Two of the pathways are C6H5NO2 C6H5 + NO2 and C6H5NO2 C6H5NO + O.The third pathway produces NO by one or both of the processes C6H5NO2 C6H5O + NO and C6H5NO2 C5H5 + CO + NO.The relative yield of the pathways producing NO2 and NO varies strongly with the photolysis wavelength.The production of NO2 exceeds that of NO by about 50percent for the 280 nm photolysis, but increases to almost a sixfold excess in 222 nm dissociation.The second pathways has a threshold energy that is about 0.50 eV greater that the thermodynamic limit for the formation of nitrosobenzene (C6H5NO) and an oxygen atom from nitrobenzene, probably reflecting the energy required to produce triplet nitrosobenzene and, perhaps, a barrier to dissociation on the triplet surface.The distribution in arrival times for a fragment provides an estimate of the recoil energy at each photolysis wavelength in these experiments.The channel producing nitric oxide (NO) radicals releases a relatively large amount of kinetic energy.Assuming the channel producing nitric oxide (NO) also produces phenoxy (C6H5O), we calculate a linear increase in kinetic energy from 0.29 eV at 320 nm to 1.1 eV at 220 nm.By contrast, the other two channels release only a small amount of kinetic energy (ca. 0.1 eV) at all wavelengths.An impulsive model does not describe the observed kinetic energy release for these low energy channels, suggesting that the energy release is more nearly statistical.The recoil energy predicted by an impulsive model for the channel producing nitric oxide and phenoxy radicals is closer to the observed kinetic energy release.
Iodine Atoms and Iodomethane Radical Cations: Their Formation in the Pulse Radiolysis of Iodomethane in Organic Solvents, Their Complexes, and Their Reactivity with Organic Reductants
Shoute, Lian C. T.,Neta, P.
, p. 4411 - 4414 (1991)
Pulse radiolysis of iodomethane in various organic solvents leads to formation of iodine atoms or iodomethane radical cations, which in turn form complexes with iodomethane or with the solvent.Radiolysis in cyclohexane gives CH3I*I, which exhibits an absorption peak at 390 nm, whereas radiolysis in benzene forms the solvent complex, C6H6*I, which exhibits an intense broad absorption centered at 490 nm.Radiolysis of iodomethane in acetone, benzonitrile, and halogenated hydrocarbons results in formation of the radical cation CH3I.+.In the former two solvents, this species forms a complex with another molecule of iodomethane to give (CH3))2+, which absorbs at 420 nm, in agreement with previous results in aqueous solutions, but in halogenated hydrocarbons it forms complexes with the solvents, absorbing at 320-360 nm, i.e. near the absorption of monomeric CH3I.+ in water.Complexes of I atoms oxidize phenol and triphenylamine relatively slowly whereas complexes of CH3I.+ react more rapidly.The reactivity of the CH3I.+*RX complexes increases in the order of RX = CH2Cl2, CHCl3, CH2Br2, CCl4, CH3I, and for each complex the reactivity with phenol increases with increase in electron donating power of substituents.Replacing the methyl group of iodomethane radical cation with ethyl or isopropyl decreases the reactivity, whereas trifluoromethyl increases the reactivity.These oxidation reactions proceed via an intermediate complex between the iodine species and the organic reductant.
Concerted proton-electron transfers. consistency between electrochemical kinetics and their homogeneous counterparts.
Costentin, Cyrille,Hajj, Viviane,Louault, Cyril,Robert, Marc,Saveant, Jean-Michel
, p. 19160 - 19167 (2011)
The concerted proton-electron transfer (CPET) oxidation of phenol with water (in water) and hydrogen phosphate as proton acceptors provides a good example for testing the consistency of the electrochemical and homogeneous approaches to a reaction, the com
Solvents Effects in the Hydrogen Abstractions by tert-Butoxy Radical: Veracity of the Reactivity/Selectivity Principle
Kim, Sung Soo,Kim, Sung Yeon,Ryou, Seung Sin,Lee, Choon Seung,Yoo, Kwang Hee
, p. 192 - 196 (1993)
The Hammett correlations and primary deuterium kinetic isotope effects were obtained to investigate the solvent effects on hydrogen abstractions from thiophenols, phenols, and toluenes by tert-butoxy radical, where the latter proved to be a more sensitive probe than the former.The limitations of the reactivity/selectivity principle are discussed in terms of either anti-Hammond effects or Marcus theory and attributed to the duality in substituent (solvent) effects.While the polar transition states for the homolytic reactions should invite dual substituent effects, the dual solvations of tert-butoxy radical could trigger the dualism of solvent effects.The influence on the rates in general may dwindle in the order of structure > substituent > solvent.
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
, p. 10746 - 10753 (2010)
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
Hydrogen hyperfine splitting constants for phenoxyl radicals by DFT methods: Regression analysis unravels hydrogen bonding effects
Amorati, Riccardo,Pedulli, Gian Franco,Guerra, Maurizio
, p. 3136 - 3141 (2010)
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 crossed molecular beams investigation of the reactions O(3P)+C6H6, C6D6
Sibener, Steven J.,Buss, Richard J.,Casavecchia, Piergiorgio,Hirooka, Tomohiko,Lee, Yuan T.
, p. 4341 - 4349 (1980)
A crossed beams investigation of the reactions of O(3P)+C6H6, C6D6 has been carried out using a seeded, supersonic, atomic oxygen nozzle beam source.Angular and velocity distributions of reaction products have been used to identify the major reaction pathways.The initially formed triplet biradical, C6H6O (C6D6O), either decays by hydrogen (deuterium) elimination or becomes stabilized, most likely by nonradiative transition to the S0 manifold of ground state phenol.CO elimination was not found to be a major channel.The branching ratio between H(D) atom elimination and stabilization was found to be sensitive to both collision energy and isotopic substitution.
Temperature Dependence of the Rate Constants for Reaction of Inorganic Radicals with Organic Reductants
Alfassi, Z. B.,Huie, R. E.,Neta, P.,Shoute, L. C. T.
, p. 8800 - 8805 (1990)
Rate constants for the reactions of several inorganic radicals with several organic reductants in aqueous solutions have been measured by pulse radiolysis as a function of temperature, generally between 5 and 75 deg C.The reactions studied were those of the radicals N3., NO2., Br2.-, I2.-, and (SCN)2.- reacting with several phenols and ascorbate.Rate constants were also measured for the reactions of Cl2.- with phenol and of ClO2. with p-methoxyphenolate.The rate constants measured were in the range of 105 to nearly 1010 M-1 s-1 and the calculated Arrhenius activation energies ranged from 7 to 41 kJ mol-1.The preexponential factors also varied considerably, with log A ranging from 9.2 to 13.9.The temperature dependences of these reactions do not seem to relate to their exothermicities.Variations in rate constants appear to be more strongly dependent on changes in preexponential factors rather than on changes in activation energy.
Rate constants and isotope effects for the reaction of H-atom abstraction from RH substrates by PINO radicals
Opeida,Litvinov, Yu. E.,Kushch,Kompanets,Shendrik,Matvienko,Novokhatko
, p. 2142 - 2149 (2016)
The kinetics of the reactions of hydrogen atom abstraction from the C–H bonds of substrates of different structures by phthalimide-N-oxyl radicals is studied. The rate constants of this reaction are measured and the kinetic isotope effects are determined.
Dramatic solvent effects on the absolute rate constants for abstraction of the hydroxylic hydrogen atom from tert-butyl hydroperoxide and phenol by the cumyloxyl radical. The role of hydrogen bonding
Avila, David V.,Ingold,Lusztyk,Green,Procopio
, p. 2929 - 2930 (1995)
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Kochi,J.K.,Krusic,P.J.
, p. 3944 - 3946 (1969)
Kinetic solvent effects on hydroxylic hydrogen atom abstractions are independent of the nature of the abstracting radical. Two extreme tests using vitamin E and phenol
Valgimigli, Luca,Banks,Ingold,Lusztyk
, p. 9966 - 9971 (1995)
Rate constants have been measured at 25°C in 13 solvents (S) for abstraction of the phenolic hydrogen atom from α-tocopherol (TOH) by tert-butoxyl (BO.) k(TOH/BO)(S), and by 2,2-diphenyl-1-picrylhydrazyl (DPPH.), k(TOH/DPPH)(S), and
Kinetic solvent effects on hydrogen abstraction from phenol by the cumyloxyl radical. Toward an understanding of the role of protic solvents
Bietti, Massimo,Salamone, Michela,Dilabio, Gino A.,Jockusch, Steffen,Turro, Nicholas J.
, p. 1267 - 1272 (2012)
A time-resolved kinetic study of the hydrogen atom abstraction reactions from phenol by the cumyloxyl radical (CumO?) was carried out in different solvents. The hydrogen atom abstraction rate constant (kH) was observed to decrease by almost 3 orders of magnitude on going from isooctane to MeOH. In TFE, MeCN/H2O 2:1, and MeOH, the measured kH values were lower than expected on the basis of the Snelgrove-Ingold (SI) equation that correlates log kH to the solvent hydrogen bond acceptor (HBA) ability parameter β2H. As these solvents also act as hydrogen bond donors (HBDs), we explored the notion that a more thorough description of solvent effects could be provided by including a solvent HBD ability term, α2H, into the SI equation via β2H(1 + α2H). The inclusion of such a term greatly improves the fitting for TFE, MeCN/H 2O 2:1, and MeOH but at the expense of that for tertiary alkanols. This finding suggests that, for the reaction of CumO? with phenol, the HBA and HBD abilities of both the solvent and the substrate could be responsible for the observed KSEs. but this requires that primary and tertiary alkanols exhibit different solvation behaviors. Possible explanations for this different behavior are explored.
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.
Laser flash photolysis study of the photochemistry of 4,5-diaza-9-fluorenone
Bertoti, Ada R.,Guimar?es, Alexandre K.,Netto-Ferreira, José Carlos
, p. 166 - 171 (2015/02/19)
The triplet excited state of 4,5-diaza-9-fluorenone (1) shows absorption maxima at 410 and 470 nm and a lifetime of 3 μs, in acetonitrile. Its intersystem crossing quantum yield was determined using 9-fluorenone as a secondary standard and a value of 0.41 ± 0.01 was obtained. The reactivity of the triplet excited state of 1 towards several quenchers, in acetonitrile, was investigated employing the laser flash photolysis technique quenching rate constants ranging from 7.9 × 104 M-1 s-1 (2-propanol) to 1.0 × 1010 M-1 s-1 (triethylamine) were obtained. From the quenching rate constants obtained one can conclude that 4,5-diaza-9-fluorenone has a ππ? triplet excited state. A Hammett plot for the quenching rate constants of triplet 1 by phenols containing polar substituents against σ + gave a reaction constant ρ of -1.54 ± 0.10, which demonstrates the electrophilic character of the 4,5-diaza-9-fluorenone triplet excited state.
