Reaction CH(3) + OH Studied over the 294-714 K Temperature and 1-100 bar Pressure Ranges

Reaction of methyl radicals with hydroxyl radicals, CH(3) + OH → products (1) was studied using pulsed laser photolysis coupled to transient UV-vis absorption spectroscopy over the 294-714 K temperature and 1-100 bar pressure ranges (bath gas He). Methyl radicals were produced by photolysis of acetone at 193.3 nm. Hydroxyl radicals were generated in reaction of electronically excited oxygen atoms O((1)D), produced in the photolysis of N(2)O at 193.3 nm, with H(2)O. Temporal profiles of CH(3) were recorded via absorption at 216.4 nm using xenon arc lamp and a spectrograph; OH radicals were monitored via transient absorption of light from a dc discharge H(2)O/Ar low pressure resonance lamp at ca. 308 nm. The absolute intensity of the photolysis light inside the reactor was determined by an accurate in situ actinometry based on the ozone formation in the presence of molecular oxygen. The results of this study indicate that the rate constant of reaction 1 is pressure independent within the studied pressure and temperature ranges and has slight negative temperature dependence, k(1) = (1.20 ± 0.20) × 10(-10)(T/300)(-0.49) cm(3) molecule(-1) s(-1).     

苯乙烯基氮氧杂芳烃间的交叉光二聚反应

用中压汞灯(λ > 300 nm)照射4-苯乙烯基吡啶、2-苯乙烯基苯并噁唑和5-苯基-2-苯乙烯基噁唑三种杂芳基乙烯单体中任意两种的硫酸水溶液，得到三种交叉二聚体.用高效液相色谱跟踪研究了交叉光二聚反应，发现每组反应生成三种光二聚体，其中二种为单体自身的光二聚体，而另外一种是两种不同单体的交叉光二聚体.交叉二聚体通过柱色谱分离得到，其顺式头对尾结构经紫外、红外、氢谱、碳谱和元素分析确定.用紫外光谱和高效液相色谱跟踪研究了交叉光二聚体的稀溶液在低压汞灯（λmax=254 nm）照射下的光解反应.研究发现交叉二聚体能够彻底发生光解，首先生成原来的反式单体，所生成的反式单体容易发生异构化而生成顺式单体，最终建立起反顺异构化平衡.     

Reaction OH + OH studied over the 298-834 K temperature and 1-100 bar pressure ranges

Self-reaction of hydroxyl radicals, OH + OH → H(2)O + O (1a) and OH + OH → H(2)O(2) (1b), was studied using pulsed laser photolysis coupled to transient UV-vis absorption spectroscopy over the 298-834 K temperature and 1-100 bar pressure ranges (bath gas He). A heatable high-pressure flow reactor was employed. Hydroxyl radicals were prepared using reaction of electronically excited oxygen atoms, O((1)D), produced in photolysis of N(2)O at 193 nm, with H(2)O. The temporal behavior of OH radicals was monitored via transient absorption of light from a dc discharge in H(2)O/Ar low-pressure resonance lamp at ca. 308 nm. The absolute intensity of the photolysis light was determined by accurate in situ actinometry based on the ozone formation in the presence of molecular oxygen. The results of this study combined with the literature data indicate that the rate constant of reaction 1a, associated with the pressure independent component, decreases with temperature within the temperature range 298-414 K and increases above 555 K. The pressure dependent rate constant for (1b) was parametrized using the Troe expression as k(1b,inf) = (2.4 ± 0.6) × 10(-11)(T/300)(-0.5) cm(3) molecule(-1) s(-1), k(1b,0) = [He] (9.0 ± 2.2) × 10(-31)(T/300)(-3.5±0.5) cm(3) molecule(-1) s(-1), F(c) = 0.37.     

Photochemistry of 2-(1-naphthyl)-2H-azirines in matrixes and in solutions: wavelength-dependent C-C and C-N bond cleavage of the azirine ring

The photochemistry of 3-methyl-2-(1-naphthyl)-2H-azirine (1a) was investigated by the direct observation of reactive intermediates in matrixes at 10 K and by the characterization of reaction products in solutions. As already reported, the photolysis of the azirine 1a with the short-wavelength light (>300 nm) caused the C-C bond cleavage of the 2H-azirine ring to produce the nitrile ylide 2. However, the products derived from the C-N bond cleavage were exclusively obtained in the irradiation of 1a with the long-wavelength light (366 nm) both in matrixes and in solutions. When 1a was irradiated in the presence of O(2) with the long-wavelength light, acetonitrile oxide (6) was produced through the capture of the biradical 4 generated by the C-N bond cleavage of 1a with O(2). An introduction of a nitro group into the naphthyl ring of 1a resulted in an acceleration of the decomposition in the long-wavelength irradiation and an extension of the wavelength region where the products derived from the C-N bond cleavage were selectively obtained. On the basis of molecular orbital calculations with the INDO/S method, the reason for the wavelength-dependent selective C-C and C-N bond cleavage of the azirine ring of 1a is discussed.     

4-(2-(4′-吡啶)乙炔)苯基重氮盐的光化学反应动力学及其自组装单分子膜的表征

以4-(2-(4′-吡啶)乙炔)苯基芳香重氮盐为研究对象,在紫外光(250W,245nm)照射下,利用紫外-可见吸收光谱对该芳香重氮盐的乙腈溶液以及自组装单分子膜室温光解反应动力学进行了研究,确定了两种状态下的光解过程都符合一级反应动力学规律,并且溶剂极性使该重氮盐更容易发生光解反应.通过X射线光电子能谱(XPS)和电化学表征证实了4-(2-(4′-吡啶)乙炔)苯基芳香重氮盐经光解反应实现对石英片和氧化铟锡导电玻璃(ITO)表面的组装修饰,得到了通过共价键与基底联结的4-(2-(4′-吡啶)乙炔)苯自组装单分子膜,从而为其后基于有机-金属层层自组装技术构筑新型功能超薄膜奠定了基础.     

Photolysis of 2,6 di-tert-butyl-4-tert-butylperoxy-4-methyl-2,5-cyclohexadienone

The photolysis of a heptane solution of 2,6-di-tert-butyl-4-tert-butylperoxy-4-methyl- 2,5-cyclohexadienone (1) with light of 360–480 nm in the presence of 2,6-di-tert-butyl-4-methylphenol or 2,4,6-tri-tert-butylphenol gives rise to their corresponding phenoxyls in a reaction with the tert-butoxyl arising in the photolysis. Direct evidence of the formation of t-BuO^. by the photolysis of 1 was provided by the ESR characterization of spin-adducts of this radical with nitrosobenzene and nitrosodurene. Evidence of the photolysis of the peroxide bond in 1 is important for the mechanism of reaction of phenolic chain-breaking antioxidants.     

Reaction mechanisms and structural characterization of the reactive intermediates observed after the photolysis of 3-(hydroxymethyl)benzophenone in acetonitrile, 2-propanol, and neutral and acidic aqueous solutions

Nanosecond time-resolved resonance Raman (ns-TR(3)) spectroscopy was employed to investigate the photoinduced reactions of 3-(hydroxymethyl)benzophenone (1) in acetonitrile, 2-propanol, and neutral and acidic aqueous solutions. Density functional theory calculations were utilized to help the interpretation of the experimental spectra. In acetonitrile, the neutral triplet state 1 [denoted here as (m-BPOH)(3)] was observed on the nanosecond to microsecond time scale. In 2-propanol this triplet state appeared to abstract a hydrogen atom from the solvent molecules to produce the aryphenyl ketyl radical of 1 (denoted here as ArPK of 1), and then this species underwent a cross-coupling reaction with the dimethylketyl radical (also formed from the hydrogen abstraction reaction) to form a long-lived light absorbing transient species that was tentatively identified to be mainly 2-(4-(hydroxy(3-(hydroxymethyl)phenyl)methylene)cyclohexa-2,5-dienyl)propan-2-ol. In 1:1 H(2)O:CH(3)CN aqueous solution at neutral pH, (m-BPOH)(3) reacted with water to produce the ArPK of 1 and then underwent further reaction to produce a long-lived light absorbing transient species. Three photochemical reactions appeared to take place after 266 nm photolysis of 1 in acidic aqueous solutions, a photoreduction reaction, an overall photohydration reaction, and a novel photoredox reaction. TR(3) experiments in 1:1 H(2)O:CH(3)CN aqueous solution at pH 2 detected a new triplet biradical species, which is associated with an unusual photoredox reaction. This reaction is observed to be the predominant reaction at pH 2 and seems to face competition from the overall photohydration reaction at pH 0.     

Mild generation of 5-(2'-deoxyuridinyl)methyl radical from a phenyl selenide precursor

[reaction: see text] 5-(2'-Deoxyuridinyl)methyl radical (1) resulting from formal hydrogen atom abstraction from the methyl group of thymidine is produced from the respective phenyl selenide precursor (2) via 350 nm photolysis or mild thermolysis (37 degrees C in the presence of glutathione) under aerobic or anaerobic conditions. The mild thermal generation of a nucleoside radical provides an alternative to previously reported photochemical methods, which are not always compatible with nucleic acids.     

NCO自由基与SO2、CS2反应的速率常数

利用波长为266 nm的激光光解CHBr3产生CH自由基,其与NO反应作为NCO自由基的来源.在298 K,总压2660 Pa的条件下,采用激光诱导荧光的方法,研究了NCO自由基与SO2、CS2的反应.得到了NCO自由基与SO2、CS2双分子反应速率常数分别为（1.8±0.3）×10－11和（3.1±0.4）×10－12 cm3•molecule－1•s－1.对这两个反应在B3LYP/6-31＋G(d)的水平上进行理论研究的结果表明,NCO自由基与SO2、CS2的反应是加成反应,其机理是NCO自由基中的N原子攻击反应物的中心原子,得到加成产物.     

N-苯基取代2,3双-[3-(1-乙基-2-甲基-吲哚)]-马来酰亚胺的合成和光致变色性能研究

有机光致变色化合物由于在光信息存储等高科技领域有着潜在的应用前景,近年来已引起了人们的极大兴趣^[1]。     

Trimethyl acetate on TiO2(110): preparation and anaerobic photolysis

The preparation and anaerobic ultraviolet photolysis of trimethyl acetate (TMA) on rutile TiO(2)(110) have been examined with an emphasis on reaction paths. Substrates for photolysis were prepared by dosing trimethyl acetic acid at 100, 300, and 550 K. The chemistry was characterized by mass spectrometry during dosing and by H(2)O adsorption and temperature programmed desorption (TPD) after dosing. Using TPD after photolysis and mass spectrometry during photolysis, the products ejected and retained during photolysis were sought. The photolysis results are interpreted using the following mechanistic model. Photons with energies exceeding 3 eV create electron-hole pairs in the substrate. With probabilities of 10(-5) or lower, the holes initiate TMA chemistry by extracting an electron from the pi orbital of the carboxylate moiety. The accompanying electrons are trapped at the surface and inhibit subsequent events of this chemistry. The electron-deficient intermediate, TMA, decarboxylates to form CO(2) and either chemisorbed tert-butyl (-C(CH(3))(3)) or physisorbed i-butene. For photolysis at 100 or 200 K, the -C(CH(3))(3) accumulates and there is a slow photon-driven secondary reaction that, with a source of H, hydrogenates adsorbed tert-butyl to physisorbed i-butane. For photolysis at 300 K, -C(CH(3))(3) thermally reacts to form and desorb i-butene and i-butane during photolysis.     

Visible light-induced degradation of ethylene glycol on nitrogen-doped TiO2 powders

The photocatalytic degradation processes of ethylene glycol (EG) during the UV or visible light irradiation of pure anatase and nitrogen (N)-doped TiO2 powders (TiO(2-x)N(x), x = 0, 0.002, 0.003, and 0.007) were investigated using time-resolved diffuse reflectance (TDR) and solid-state NMR spectroscopies. The TDR spectra and time traces observed for the charge carriers indicated that the scavenging of photogenerated holes (h+) by EG occurred during the 355-nm laser photolysis of the N-doped TiO2 powders, while no direct oxidation reaction of EG by h+ occurred during the 460-nm laser photolysis, although the charge carriers were sufficiently generated upon excitation. The solid-state magic-angle spinning (MAS) NMR measurements revealed that EG is preferentially chemisorbed on the surface of the N-doped TiO2 powders, in contrast to the pure TiO2, and degrades under visible light irradiation.     

Preparation and photochemical properties of poly[2-(4-benzoylphenyl)-2-(4-propenoylphenyl)-propane] and its copolymer with styrene

2-(4-Benzoylphenyl)-2-phenyl propane ( 4 ) was prepared by benzoylation of 2,2-diphenylpropane ( 2 ). Acylation of ( 4 ) with 3-chloropropanoic chloride gave 2-(4-benzoylphenyl)-2-(4-propenoylphenyl)propane ( 5 ). A monomer 2-(4-benzoylphenyl)-2-(4-propenoylphenyl)propane ( 6 ) was prepared through dehydrochlorination of ( 5 ). The homopolymer of 6 (P6) and the copolymer with styrene ( P6 / S) were prepared by radical polymerization. Laser flash photolysis was employed to determine the absorption and emission spectra of transients, their lifetimes (τ) and the rate constant (k_q) of triplet quenching in benzene at laboratory temperature for 4 , P6 , and P6 / S. P6 exhibits a transient absorption maximum in a different spectral region than do the model 4 and copolymer P6/S . The products of k_q and τ determined by laser flash photolysis for these transients are higher than th Stern–Volmer constants based on inhibition of degradation. Degradation leading to formation of quenchers is the likely cause of this difference although crosslinking may also contribute. Irradiation of polymers ( P6 and P6/S ) at 366 nm leads to main chain scission with aquantum yield of 0.13 under N₂ for P6 and 0.03 for P6/S . In this bichromophoric structural unit, the benzophenone residue absorbs about 80–90% of the incident energy. Its triplet energy is about 5 kJ mol^?1 lower than that of the 1-(4-alkylphenyl)-2-propene-1-one chromophore. Different possible pathways of degradation are discussed namely the Norrish Type II reaction of the alkyl aryl ketone and direct reaction of triplet benzophenone with the main chain. In the mechanism favored the benzophenone triplet is proposed to be in equilibrium with the upper acetophenone-like chromophore from which the Norrish Type II reaction leading to chain fragmentation takes place.     

LUMIFLAVIN-SENSITIZED PHOTOOXYGENATION OF INDOLE

Abstract— The lumiflavin-sensitized photooxygenation of indole in aqueous solutions has been investigated by means of steady light photolysis and flash photolysis. The semiquinone of lumiflavin and the half-oxidized radical of indole were formed by the reaction between triplet lumiflavin and indole (3.7 times 10⁹ M ^-1 s^-1). The semiquinone anion radical of lumiflavin reacted with oxygen to form superoxide radical. The triplet state of lumiflavin also reacted with oxygen forming singlet oxygen, ¹O₂. But the reaction between ¹O₂ and indole (7 times 10⁷ M^_l s^_1; estimated from steady light photolysis using Rose Bengal as a sensitizer) was far less efficient than the reaction between indole and triplet lumiflavin. The quantum yield of the lumiflavin-sensitized photooxygenation of dilute indole via radical processes was much higher than that via ¹O₂ processes, though appreciable ¹O₂ was formed.     

LIGHT-MEDIATED CYCLIZATION OF (E)-3-(5-[6-HYDROXY-7-METHOXY] BENZOFURANYL)PROPENOIC ACID, A WATER-SOLUBLE PRECURSOR OF 8-METHOXYPSORALEN

The title compound is a stable, water-soluble "pro-drug" for 8-methoxypsoralen, which converts to psoralen upon photolysis with UVA light. The process involves the photolytic formation of a cis isomer that lactonizes in a dark reaction.     

Experimental and theoretical investigation of rate coefficients of the reaction S(3P)+OCS in the temperature range of 298-985 K

The reaction S(3P)+OCS in Ar was investigated over the pressure range of 50-710 Torr and the temperature range of 298-985 K with the laser photolysis technique. S atoms were generated by photolysis of OCS with light at 248 nm from a KrF excimer laser; their concentration was monitored via resonance fluorescence excited by atomic emission of S produced from microwave-discharged SO2. At pressures less than 250 Torr, our measurements give k(298 K)=(2.7+/-0.5)x10(-15) cm3 molecule-1 s-1, in satisfactory agreement with a previous report by Klemm and Davis [J. Phys. Chem. 78, 1137 (1974)]. New data determined for 407-985 K connect rate coefficients reported previously for T>or=860 and Tor=500 Torr, the reaction rate was enhanced. Theoretical calculations at the G2M(CC2) level, using geometries optimized with the B3LYP6-311+G(3df) method, yield energies of transition states and products relative to those of the reactants. Rate coefficients predicted with multichannel Rice-Ramsperger-Kassel-Marcus (RRKM) calculations agree satisfactorily with experimental observations. According to our calculations, the singlet channel involving formation of SSCO followed by direct dissociation into S2(a 1Deltag)+CO dominates below 2000 K; SSCO is formed via intersystem crossing from the triplet surface. At low temperature and under high pressure the stabilization of OCS2, formed via isomerization of SSCO, becomes important; its formation and further reaction with S atoms partially account for the observed increase in the rate coefficient under such conditions.     

Studies on Debenzylation and Photolysis of 1-Benzyl- and 1-(β-Phenethyl)-1,2,3,4-tetrahydroisoquinolines

Debenzylation of 1-(3-benzyloxybenzyl)-1,2,3,4-tetrahydroisoquinolines 1 , 6 , 7 with hydrochloric acid and ethanol gave the corresponding phenolic isoquinolines 2 , 8 , 9 and tetrahydroprotoberberines 4 , 12 , 13 . Compounds 2 , 8 , 9 on photolysis also gave, besides the expected noraporphines 3 , 10 , 11 , the tetrahydroprotoberberines 4 , 12 , 13 [1–4] (Schemes 1 and 2). 6-Benzyloxy-1-(5-benzyloxy-2-bromo-benzyl)-1,2,3,4-tetrahydroisoquinoline (27a) containing no methoxy or methylenedioxy groups either in ring A or C does not give protoberberine during debenzylation; but 28 , the debenzylation product of 27a , on photolysis gives both the noraporphine 29 and the tetrahydroprotoberberine 30 (Scheme 6), proving that during debenzylation of 1-(3-benzyloxybenzyl)-1,2,3,4-tetrahydroisoquinolines containing additional methoxy or methylenedioxy groups, the necessary formaldehyde comes from the latter groups. During photolysis both the methoxy groups (methylenedioxy groups) and the C(3) atom of the tetrahydroisoquinoline moiety provide the formaldehyde. Veratrole under debenzylation and photolytic conditions and tetrahydroisoquinoline under the latter condition also give rise to formaldehyde (Schemes 8 and 10). The novel bromohomoprotoberberine 43 along with 42 was formed during debenzylation of the 1-phenethyl-1,2,3,4-tetrahydroisoquinoline 41 . Photolysis of 42 yielded the novel nor-homoaporphine 44 , in addition to 43 ; the latter was debrominated to give the homoberbine 45 .     

Photoinduced [3+2] Cycloaddition of Carbenes and Nitriles: A Versatile Approach to Oxazole Synthesis

We have developed a photoinduced protocol for the synthesis of pharmaceutically important oxazole molecules using diazo- and nitrile-containing reactants. The process involves the initial photolysis of the diazo compound to afford singlet carbenes, which are tapped by nitriles in a [3+2] cycloaddition fashion to give substituted oxazoles. With di-nitrile compounds, useful bis-oxazoles were obtained. The applicability of the transformation is showcased through the expedient synthesis of small-molecule drugs and biologically relevant molecules such as felbinac, pimprinine, texamine, ugnenenazole etc. The protocol is also useful for the generation of ²H and ¹³C isotope labelled oxazoles. Merging photolysis with continuous-flow chemistry was demonstrated for scaling up the reaction. The non-requirement of metal catalysis or photosensitizers to harness the light energy with blue light sufficing the execution of the reaction makes it a versatile and general protocol for the synthesis of structurally diverse oxazoles     

Effect of Nitrate Ions on the Chain Photochemical Reaction of Sulfo Group Substitution for Bromine in 1-Bromo-2-Hydroxynaphthalene upon Sensitized and Direct Photolysis

The influence of nitrate ion admixtures on the proceeding of the radical-ion chain reaction of sulfo group substitution for halogen in halogenated hydroxynaphthalenes in an aqueous sodium sulfite solution was studied upon both direct and tris(2,2-bipyridyl)ruthenium(II)-sensitized photolysis. It was found that nitrate ions increase the quantum yields of the photosensitized substitution reaction and decrease the quantum yields of the reaction in the direct photolysis. Based on an analysis of kinetic schemes of the reaction, it was shown that nitrate ions affect the photoinitiation step in sensitized photolysis or the termination step in the direct photolysis.     

CH2((X)3B1)自由基与N2O反应的研究

The reaction dynamics of methylene radicalCH2((x)3B1)with N2O was investigated by Time Resolved Fourier Transform Infrared Spectroscopy(TR-FTIRS). Pure CH2((x)3B1) radical was produced via laser photolysis of ketene at 351 nm.. Nascent vibrationally excited products CO , NO and HCN were observed.. Some reaction pathways which may lead to these products were proposed and a possible reaction mechanism was outlined..