Photochemical Reactions of Linear Alkane Radical Cations in Low-Temperature Matrices

The radical cations of linear alkanes (n-pentane, n-heptane) trapped in various matrices (Freon-11, Freon-113, Freon-113a, mixture of Freon-11 and Freon-114B2, and sulfur hexafluoride) were found to undergo the following types of photochemical reactions: (1) charge transfer to the matrix followed by neutralization, (2) isomerization and unimolecular decomposition, and (3) deprotonation. The absorption spectra of the radical cations were characterized, and the quantum yields of reactions occurring in different matrices at 77 K were determined. It was shown that the reaction pathway and efficiency of the photochemical processes observed for a given radical cation in different matrices with similar physical and chemical characteristics could considerably differ.     

Photochemical transformations of cyclic acetal radical cations in Freon matrices at 77 K

The efficiency of photochemical reactions of radical cations of cyclic acetals (1,3-dioxolane, 1,3-dioxane) is measured in different Freon matrices at 77 K and the influence of the latter on the reaction path is discovered. The possible nature of the paramagnetic complexes that form in photochemical reactions of cyclic acetal radical cations in Freon-11 is suggested.     

Reactions of the primary radical cations of carboxylic acids as studied by ESR in freonic matrices

Radical products of radiolysis of frozen solutions of propionic and butyric acids were studied in the matrices of Freon-11, Freon-113, and Freon-113a at 77 K. It was shown that the primary radical cations generated by radiation were not trapped in the freonic matrices (in contrast with the corresponding freonic solutions of acetic acid). The radical cations of propionic and butyric acids decay in concurrent processes of rearrangements yielding terminal-type and ylide-type distonic radical cations and intramolecular proton transfer in the dimeric radical cations resulting in acyloxy radicals. The latter species undergo decarboxylation to yield ethyl and propyl radicals for propionic and butyric acids, respectively. According to mass-spectrometric data, the terminal-type distonic radical cations undergo the McLafferty rearrangement.Translated from Khimiya Vysokikh Energii, Vol. 39, No. 2, 2005, pp. 97–104.Original Russian Text Copyright © 2005 by Belevskii, Belopushkin.This revised version was published online in April 2005 with a corrected cover date.     

The gas chromatographic separation of anaesthetic agents and aerosol propellants in operating room air using serially packed columns

The use of gas chromatographic columns serially packed with molecular sieve 5A and Porapak-Q (both with particle sizes in the range 50–80 mesh) is described for the analysis of operating theatre air for nitrous oxide, halothane, trichloroethylene, enflurane, Freon-11 and Freon-12. Various combinations of lengths of the two packings were evaluated; the most suitable was 2.75 m of Porapak-Q and 0.29 m of molecular sieve 5A with a column temperature of 250°C. With the electron capture detector used, the optimum temperature to give high sensitivity for nitrous oxide was 350°C.     

Ozonides of perfluorooct-1-ene and perfluorooct-2-ene

Ozonides of higher perfluoroalkenes were prepared for the first time by ozonation of perfluorooct-1-and-2-enes in Freon-113. The structures of the resulting compounds were confirmed by¹³C NMR spectroscopy and GLC-mass spectrometry.     

F114双通道激光解离的动力学研究

本文用TEA CO_2激光器研究了F_(114)(氟利昂-114)激光解离的通道竞争动力学过程。实验发现, F_(114)的激光解离是C—C链和C—Cl键断裂的双通道竞争过程; 其解离过程可以用Arrhenius公式来描述, 并且激光解离的表观活化能与热解离活化能相近, 因而该解离反应具有明显的热解离行为。理论计算还表明, F_(114)的双通道解离过程基本上符合RRKM理论。     

Ozonolysis of Alkenes and Studies of Reactions of Polyfunctional Compounds: LXV. Ozonolysis of Perfluoro-1-octene in Freon-113

Ozonization of perfluoro-1-octene in Freon-113 yields the corresponding ozonide whose catalytic hydrogenation over Pd/C or hydride reduction leads to formation of perfluoroheptanoic acid; the reduction with lithium aluminum hydride gives 2,2,3,3,4,4,5,5,6,6,7,7,7-tridecafluoro-1-heptanol. Ozonization of perfluoro-1-octene in Freon-113 containing excess (3 equiv) alcohol affords the corresponding perfluoroheptanoic acid ester.     

ZnO纳米粒子多相催化n-C7H16-SO2气相光化学反应的研究

利用自制的ZnO纳米粒子和商品的ZnO粒子，研究了ZnO粒子多相催化n-C6H16- SO2的气相光化学反应。利用气相色谱－质谱联用仪（GC／MS）和气相色谱仪（GC ）对反应物n-C6H16和SO2以及主要气相产物3－庚酮进行了定量分析，考察了不同 条件下它们的降解和产生趋势，初步探讨了氧气和水蒸气对ZnO粒子多相催化n- C7H16-SO2气相光化学反应的影响，并对反应的一些现象作了描述及相应的说明。 结果表明，无论有无氧化存在，ZnO粒子均能够对n-C7H16-SO2的气相光化学反应起 一定的催化作用，但是有氧气的催化活性比无氧气的高。这可能说明了ZnO的光催 化作用主要与生成的活性氧物种（O^*)有关，同时光致空穴（h^+）也能够直接引 发氧化反应；虽然ZnO纳米粒子的光催化活性随着焙烧温度的升高而降低，但是均 比商品的高。而在模拟大气的条件下，ZnO纳米粒子对n-C7H16SO2的气相光化学反 应有很大的影响，大大地促进了n-C7H16和SO2的降解，这说明ZnO纳米粒子的存在 对大气中SO2－烃的气相光化学反应的影响是不容忽视的。此外，对ZnO粒子多相催 化n-C7H16-SO2气相光化学反应的机理进行了探讨。     

ON THE ORIGIN OF LASER-SPECIFIC LUMINESCENCE UPON PULSED-LASER EXCITATION OF BENZOPHENONES IN FREONS†

–Excimer laser excitation (308 nm) of benzophenone in Freon-113, as well as in Freon-11, results in an intense emission with λ_max at approx. 530 nm in addition to triplet phosphorescence. This emission is shown to result from an excited free radical bearing the diphenylmethylene moiety which is generated in a two-photon process and which luminesces upon sensitization by the benzophenone triplet. On the basis of its spectroscopic properties and the chemical nature of the system, it is suggested that the fluorescer in this system may be the hypochlorite radical, Ph₂COCl.     

Features in the vibrational relaxation of laser excited Freon-22 molecules

The vibration-translation (V-T) of laser excited Freon-22 (CF₂HC1) molecules has been studied. An interferometric technique allows simultaneous measurement of the initial energy 〈E〉 stored in the molecules, and of the V-T relaxation time. Consequently, the V-T relaxation time and the energy released per collision can be determined as a function of the energy absorbed from the laser field. Three distinct regions have been observed for these dependences. This behaviour observed and reported by us for Freon-22 confirms the role played in the relaxation process by the initial distribution of the vibrational energy, and agrees qualitatively with the experimental results for other polyatomic molecules.     

A search for dichlorocarbene ether solvent interactions

The absolute rate constant of reaction of dichlorocarbene with pyridine and with tetramethylethylene was determined in Freon-113 (CF₂ClCFCl₂), dioxane, and tetrahydrofuran. No evidence of specific solvation was obtained.     

超分子体系中的光物理和光化学过程

总结了我们组近几年来对超分子体系中的光物理和光化学过程所做的工作,包括三个部分：(1)微反应器控制的有机光化学反应的选择性,(2)疏水、疏脂作用对光物理和光化学过程的影响,(3)超分子体系中的电子转移、能量传递和光化学转换。     

Stabilization and reactions of tetramethylurea radical cations in Freon matrices at 77 K: Intramolecular hydrogen transfer,ion-molecular reactions,and fragmentation by electron spin resonance study

ESR spectra for -irradiated at 77 K solutions /0.02–16%/ of tetramethylurea /TMU/ in CFCl₃ and Freon-113 have been studied. TMU^+. radical cations radiolytically produced in dilute solutions have been shown to undergo intramolecular hydrogen transfer upon photobleaching resulting in CH₂N= type radical. Evidence for intermolecular proton transfer in TMU^+. radical cations after annealing to phase transition temperature /110–120 K/ in Freon-113 was obtained. Primary radical cations of TMU^+. at their ground state take part in ion-molecular reaction via proton transfer. Molecular cations in their excited states may undergo fragmentation producing Me₂N radicals, which were trapped in liquid phase by t-BuNO as a spin trap.     

Pattern recognition for analysis of cigarette smoke by capillary gas chromatography. Part 1: Total particulate matter (TPM)

Complex smoke profiles from fused silica capillary gas chromatography of different cigarette types produce rich information requiring computer and sophisticated statistical analysis to reveal the hidden correlation patterns. In our technique, a Cambridge pad containing total particulate matter (TPM) is extracted with Freon-11 in a micro-Soxhlet apparatus. The condenser is maintained at ?15°C. After extraction, Freon-11 is allowed to evaporate under mild conditions. Bis(trimethylsilyl)trifuoroacetamide (BSTFA) is subsequently added to the extract. Trimethylsilylation is completed by maintaining the reaction vessel at 60°C for two hours. A microprocessor-controlled capillary gas chromatograph with an automatic sampler is used to generate profiles. A link to a host computer provides for transmission of profile reports and access to various statistical and graphic packages. Factor and discriminant analyses are applied to gas chromatographic data from TPM extracts because of their ability in data reduction, pattern extraction and ranking the importance of the gas chromatographic peaks. Some preliminary results from these statistical analyses are discussed.     

SOME FUROCOUMARINS AND ANALOGS: COMPARISON OF TRIPLET PROPERTIES IN SOLUTION WITH PHOTOBIOLOGICAL ACTIVITIES IN YEAST

Abstract— Some photophysical and photochemical properties of two furocoumarins, three furochro-menes and one difurobenzene have been studied in ethanol by laser flash spectroscopy. Such properties included the triplet absorption spectra. extinction coefficients, quantum yields of formation and reactivities with the nucleic acid bases thymine and uracil, and the amino acid tryptophan. The effects the same compounds have on survival of the yeast, Saccharomyces cerevisiae , after 365 nm photosensitization were also investigated. These effects on survival differed markedly for the different compounds. Possible correlations between the photophysical, photochemical and photobiological data are discussed.     

Determination of DNA using sodium 9,10-anthraquinone-2-sulfonate as an in situ photochemical fluorescence probe

An in situ photochemical fluorescence probe method for the determination of DNA with sodium 9,10-anthraquinone-2-sulfonate (AQS) as a photochemical fluorescence probe was developed. It was based on the conversion of AQS into an intensively fluorescent product by irradiating with UV radiation. The photochemical reaction is retarded by DNA. The determination can be carried out by measuring the fluorescence intensity at a fixed time. The calibration graph was linear in the range 0–80 ng ml⁻¹ calf thymus (CT) DNA (r = 0.9991), the limit of detection was 3.2 ng ml⁻¹ CT DNA (n = 9). The kinetic behaviour of the photochemical reaction and the effects of experimental conditions were investigated and discussed in detail. The results of absorption spectra and competitive binding experiments suggested the interaction between AQS and DNA to be intercalative.     

Mechanistic Aspects of the Effects of Stress on the Rates of Photochemical Degradation Reactions in Polymers

Abstract

This review examines the mechanistic origins of the effects of stress on the photochemical degradation rates of polymers. Recent studies have shown that tensile and shear stresses accelerate the rate of the photochemical degradation of polymers. Conversely, compressive stress generally retards the rate of photochemical degradation. After an initial discussion of the photochemical auto‐oxidation mechanism, the three primary hypotheses that purport to explain how stress affects photochemical degradation are examined. The first hypothesis is attributed to Plotnikov, who proposed that stress changes the quantum yields of the reactions that lead to bond photolysis. The second hypothesis, attributed to a number of researchers, says that stress affects the ability of the geminate radical pairs, formed in the photochemical bond cleavage reactions, to recombine. The third hypothesis proposes that stress changes the rates of radical reactions subsequent to radical formation. A further attempt to account for the effects of stress on degradation rates is a modification of the so‐called Zhurkov equation that has been used rather successfully to predict the effects of stress on degradation rates in thermal reactions. This empirical equation relates the quantum yield of degradation to a composite activation barrier for the overall photochemical reaction. Following the discussion of these hypotheses, experimental mechanistic studies of stress effects are summarized, and what little data there is is shown to be consistent with the hypothesis that proposes that stress primarily affects the ability of photochemically generated radical pairs to recombine. By decreasing the efficiency of radical–radical recombination, the effect is to increase the relative efficiencies of the radicals' other reactions and hence the rate of degradation. In addition to stress, other factors can affect the rates of polymer photodegradation. These factors include the absorbed light intensity, the polymer morphology, the rate of oxygen diffusion in the polymer, and the chromophore concentration. Each of these parameters must be carefully controlled in mechanistic studies that probe the effects of stress on degradation rates.     

芳砜在微环境中的光化学反应

本文研究了十二烷基磺酸钠-正戊醇-水三组分体系相图, 并用小角度X衍射仪确定了相图中液晶区域为层状。在不同微环境(W/O型微乳液、液晶、O/W型微乳液)中, 研究了对甲基苄基苄基砜(ASO2B)的光化学反应影响。结果发现微环境对反应产物分布(笼效应)有很大影响。外加磁场明显降低笼效应。证实了芳砜的光化学反应经历自由基中间体, 并且反应的激发态为三重态。     

Ozonolysis of perfluoroalkenes and perfluorocycloalkenes

Ozonolysis of 1-methoxyperfluorocyclobutene in Freon-113 followed by hydrogenation of the reaction products gave methyl hydrogen perfluorosuccinate. Under similar conditions, perfluorooct-1- and-2-enes and 4-trifluoromethyl-1,1,1,2,3,4,5,5,5-nonafluoropent-2-ene were converted into perfluorinated heptanoic, hexanoic, and isobutyric acids, respectively. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1239–1241, June, 1997.     

Isotopic effects due to energy transfer in photechemical reactions

Strong H/D isotopic effects were observed in photochemical decomposition of acetaldehyde and some other organic substances at 77 and 4.2 K. The value of the isotopic effect increased considerably over the temperature range 77 to 4.2 K and remained constant over a wide range of the isotopic molecule ratio as was shown for acetaldehyde. The results obtained were explained in terms of trapping the electron excitation by molecules with lighter isotopes which are known to have, as a rule, lower excitation energy. A theory was developed taking into account the migration of the electron excitation among similar molecules, the energy exchange between two isotopic species, and their photochemical decomposition. The temperature and concentration dependences of the isotopic effects predicted by the theory were in accord with experiment.