Semiconductor-catalyzed photooxygenation of aromatic olefins

Irradiation of semiconductors (TiO₂ and CdS) suspended in organic solvents containing 1,1-diphenylethylene and its derivatives under oxygen afforded the corresponding epoxides and benzophenone. A possible mechanism is discussed.     

Effect of the structure of reactants on the reaction rate constants of aromatic nitroso oxides with olefins

The reactivity of phenylnitroso oxide, (p-methylphenyl)nitroso oxide, (p-nitrophenyl)nitroso oxide, (m-nitrophenyl)nitroso oxide, and (p-bromophenyl)nitroso oxide toward a number of olefins in acetonitrile at room temperature was studied using flash photolysis. It was found that the reaction rate constant decreased with decreasing energy of a molecular orbital with a maximum contribution from the atomic orbitals of carbon atoms in the C=C bond of olefins. This, along with a positive slope of the Hammett function for the reactions of substituted phenylnitroso oxides with 1-hexene and styrene, suggest an electrophilic character of these species. The temperature dependence of the rate constant of the reaction of phenylnitroso oxide with 1-hexene was studied: log A = 7.9 ± 0.4 [l mol^-1 s^-1]; E_a = 38 ± 2 kJ/mol.Translated from Kinetika i Kataliz, Vol. 45, No. 6, 2004, pp. 842–847.Original Russian Text Copyright © 2004 by Chainikova, Khursan, Safiullin.     

Autoxidation of cyclic olefins in perfluorinated organic solvents

It is well known that several perfluorinated organic compounds (particularly alcanes and cyclic ethers perfluor$\text{i}$nated) have specific properties like solvents of biatomic gas and oxygen.Since these perfluorinated compounds have also suff$\text{i}$cient capabilities as solvents of several alifatic hydr$\text{o}$carbons and pratically none as solvents of their oxidation products (alcohols, ketones; peroxides, acids, water, etc.), these solvents seem ideal for the studying of oxidation reactions in liquid phase.The kinetics of autoxidation, with O₂ for temperatures between 15°C and 60°C, of cyclohexene and methyl cyclohexenes, have been studied in fluorinated solvents (various mixtures of 3,n-perfluoro-propyl-perfluoro-tetrahydrofuran, and 3,n-perfluoro-buthyl-perfluoro-tetrahydropyran) with formula C₈F₁₆O. This study includes the determination of the kinetic parameters both during the induction phase and during the stationary phase.The above mentioned oxidations we have studied in anal$\text{o}$gous conditions in other solvents (carbon tetrachloride, benzene chloride, etc.). The highest rates observed and the larger selectivity of the fluorinated solvents have been pointed out.     

血红蛋白在有机溶剂中的电化学行为及其类酶电催化研究

本文研究了Hb/Sol-gel膜修饰碳糊电极在有机溶剂介质中的直接电化学和类过氧化物酶电催化特性。发现在以甲醇、正内醇和乙腈介质中,Hb修饰电极能够实现其与电极之间的直接电子转移,并且电子转移的动力学过程与水溶液体系相似。然而,在这些有机溶剂介质中,电子转移的可逆性不如水介质中好,同时氧化还原峰电位差均不大于水溶液体系,表明有机溶剂对Hb的直接电子转移产生抑制作用。Hb/Sol-gel修饰电极在有机溶剂介质中和水介质中一样,对其特异性底物H2O2产生过氧化物酶的活性,但其活性均不如水溶液体系强。     

Use of solvents in the low-pressure plasma oxidation of olefins

The oxidation ofn-octene has been studied in mixtures with dimethylbutane, 1,4-dimethylcyclohexane, ethylcyclohexane, and dibutyl ether. Except for dimethylbutane, total yields increase on addition of a solvent, and the fraction of epoxide among the products is higher than in reactions with neat octene.     

Transient Radicals Formed by Electron Transfer between inorganic ions and excited aromatic molecules in polar solvents

Fluorescence quenching of aromatic molecules by inorganic anions has been the subject of many investigations, yet the nature of the quenching mechanism is not fully understood. The fluorescence-quenching rate constants correlate with electrochemical data, but the radicals expected to form upon transfer of an electron to the excited aromatic molecules have escaped observation. We report the first observation of radical-ion species formed by electron-transfer quenching with inorganic anions in acetonitrile. A decisive step leading to formation of separated radical ions is the trapping of the primary charge-transfer complex by a second inorganic ion.     

Effect of protonation on the electronic structure of aromatic molecules: naphthaleneH+

Protonated naphthalene, the smallest protonated polycyclic aromatic hydrocarbon cation, absorbs in the visible, around 500 nm, which corresponds to an unusually large red shift with respect to the neutral naphthalene counterpart.     

Spin-lattice relaxation and rotational motion of aromatic triplet-state molecules in supercooled alkane solvents (part 1)

The phosphorescence of phenazine (PZ) and quinoxaline (QX) was investigated after pulsed laser excitation in the glass-transition range of several alkane solvents. Three relaxation processes of PZ and QX in the metastable triplet state, T1, were studied as a function of temperature: (1) the decay of the selective population of the strongly phosphorescent triplet substate T1x due to spin-lattice relaxation (SLR), (2) the time-dependent red shift of the phosphorescence spectrum due to the solvation of triplet-state molecules, and (3) the decay of the phosphorescence polarization due to orientational relaxation (OR). Various aspects and connections of the mechanisms governing the three relaxation phenomena are discussed. The relaxation dynamics were characterized at temperatures above the glass-transition temperature of the respective solvent, where the fundamental processes involved are strongly dependent upon the solvent viscosities. For the systems treated here, OR and solvation were satisfactorily described by a Vogel-Fulcher-Tammann temperature behavior. SLR also depends on properties of the alkane solvent above the glass transition. Upon cooling, SLR becomes independent of the specific solvent properties and is based on mechanisms that are typical for amorphous glasses or solids. (This particular aspect will be the subject of a subsequent publication, part 2).     

Properties and structure of aromatic ester solvents

This paper reports on an experimental and theoretical study of the aromatic ester solvents family. Several compounds were selected to analyze the different factors that influence their liquid-state properties and structures. The pressure-volume-temperature behavior of these fluids was measured accurately over wide temperature and pressure ranges and correlated successfully with the empirical TRIDEN equation. From the measured data the relevant derived coefficients of isothermal compressibility, isobaric expansibility, and internal pressure were calculated. The statistical associating fluid theory (SAFT) and perturbed chain statistical associating fluid theory (PC-SAFT) molecularly based equations of state were used to predict the PVT behavior with model parameters obtained from the correlation of available saturation literature data; the results provided by PC-SAFT equations of state were clearly superior for all of the studied solvents. The fluid's molecular level structure was studied by quantum computations at the B3LYP/6-311++g** level and classical molecular dynamics simulations in the NPT ensemble with the OPLS-AA forcefield. Molecular parameters, such as torsional barriers or cluster energetics, were analyzed as a function of ester structures. The molecular dynamics study provides, on one hand, theoretical values of thermophysical properties, which are compared with the experimental ones, and, on the other hand, valuable molecular level structural information. On the basis of both macroscopic and microscopic studies complex fluid structures were inferred with important effects arising from the geometries of the studied molecules and from the existence of remarkable intermolecular forces of dominating dipolar nature.     

Photochemical incorporation of protic solvents by open chain olefins

Irradition of methyl styryl sulphoxide dissolved in MeOH, EtOH, or AcOH induces the photochemical polar addition of the solvents to afford the product, PhCH(OR)CH₂SOMe, where R is Me, Et, or Ac. By-products are the corresponding sulphides, PhCH(OR)CH₂SMe, and methyl styryl sulphide. Similar adducts of protic solvents are produced upon irradiation of certain vinylic sulphides, methyl phenethynyl sulphide, as well as appropriately substituted propenylbenzenes including o-anethole, o-anol, and o-propenylaniline in soln.     

Photodimerizatiom of thiochromone in aromatic solvents

Photolysis of thiochromone $\text{1a}$ in several aromatic solvents of widely differing ionization potentials leads to the formation of mixtures of all four possible cyclobutane photodimers. In sharp contrast to the photochemical behavior of the analogous sulfone, no evidence for {2+2}, or for substitutive, photoaddition reactions was found.     

Conformation calculations on strained aromatic molecules

Interaction potentials for unconnected atoms are refined, together with the elastic constants needed to calculate conformations for strained molecules from the mechanical model. Equilibrium configurations are derived for octachloronaphthalene, 1, 4, 5, 8-tetrabromonaphthalene, 3, 5-dichloroanthracene, benzene halides, 2, 2-paracyclophane, diphenyl, and 5, 6-dichloro-11, 12-diphenylnaphthacene. The results agree satisfactorily with experiment. It is concluded that the model allows interpretation and a priori prediction of conformations for strained aromatic systems.     

Monitoring the electrochemistry of single molecules by surface-enhanced Raman spectroscopy

Coherent control of chemical species in complex systems is always subject to intrinsic inhomogeneities from the environment. For example, slight chemical modifications can decisively affect transport properties of molecules on surfaces. Hence, single-molecule (SM) studies are the best solution to avoid these problems and to study diverse phenomena in biology, physics, and chemistry. Along these lines, monitoring SM redox processes has always been a "holy grail" in electrochemistry. To date, claims of SM electrochemistry by spectroscopy have come only from fluorescence quenching of polymers and redox-fluorescent molecules. In unconnected developments, the potential of the bianalyte surface-enhanced Raman scattering (SERS) method as a technique with SM sensitivity has been demonstrated. Raman spectroscopy has the potential to explore SM detection of any molecule, independent of its chemical nature. We provide definitive proof of SM events following redox cycles using SERS. The superior sensitivity and spectral richness of SERS makes it general enough to study, in principle, SM electron transfer of any (label-free) molecule.     

The amidoalkylation of aromatic compounds and olefins with 5-alkoxyhydantoins

5-Butoxyhydantoin (2a), 3-benzyl-5-methoxyhydantoin (2b) and 3-p-chlorophenyl-5-methoxy hydantoin (2c) were found to react, in the presence of an acid catalyst, with aromatic compounds and olefins to give 5-arylhydantoin (3) and 5-alkylhydantoins with an unsaturated side chain. Isomers which differ in the location of the double bond (4,5,6) as well as cis-trans isomers were isolated and characterized.     

On the photonics of aromatic azide molecules

Energies of electronically excited states of a number of aromatic azides have been calculated using ab initio quantum-chemical methods. It has been shown that the relative arrangement of the singlet and triplet states of the A′ and A″ types changes with an increase in the number of π electrons in the system. As in the case of other classes of heteroaromatic molecules, five relative locations of these states are possible. On this basis, the dependence of the luminescent and photochemical properties of molecules of aromatic azides on their chemical structure has been rationalized.     

Kinetics and mechanism of reactions between aromatic olefins and hydroxyl radicals

The rates of the reactions of hydroxyl radicals (OH) with styrene, α-methylstyrene, and β-methylstyrene have been measured by irradiating mixtures of these aromatic olefins and NO in an environmental chamber at 298 K. Experimental conditions were used whereby the competition of ozone with OH in oxidizing the hydrocarbons could be considered negligible. The rate constant values, obtained by a relative method using isooctane as reference hydrocarbon, are: styrene (5.3 ± 0.5) × 10^?11 cm³/molec·s, α-methylstyrene (5.3 ± 0.6) × 10^?11 cm³/molec·s, and β-methylstyrene (6.0 ± 0.6) × 10^?11 cm³/molec·s. A simplified kinetic treatment of the experimental data shows that styrene and β-methylstyrene are stoichiometrically converted to benzaldehyde, suggesting that OH attack occurs only on the aliphatic moiety of the aromatic olefins. Benzaldehyde was observed to undergo consecutive oxidation by OH, and its maximum formation yield was about 60%. A reaction mechanism is proposed where the primary rate-determining OH attack leads to the formation of 1-hydroxy-2-phenyl-2-ethenyl radicals, from which benzaldehyde is formed through fast intermediate reactions.     

Conformational analysis of aromatic molecules

The mechanical model used in conformation calculations is discussed. A method is developed for strained aromatic systems with possible out-of-plane deformations. An approximate analysis is presented to reveal criteria for planarity.