The absence of ethylenedione in photochemical biscarbonylation reactions

Photolyses of a number of bridged cyclohexenediones and vinylcyclobutanediones in argon or xenon matrices at 10 K at a variety of wavelengths produced carbon monoxide with no evidence for formation of ethylenedione, the elusive dimer of CO.     

Electron transfer reactions between the superoxide ion and quinones

The electron transfer reactions of the superoxide ion with benzoquinone, trimethylbenzoquinone, and menadione in dimethylformamide were studied. A procedure of the determination of the relative rate constants of these reactions was developed; the reaction of O? ₂ with butyl bromide was chosen as a standard one. The relative rate constants measured at 20,°, 35°, and 50°C were slightly dependent on the quinone structure. The relationship between the free energy ΔF*of the electron transfer reactions and the standard free energy ΔF^o was discussed. This relationship is proposed as ΔF* = αΔF^o + β, where the proportionality coefficient α is equal to 0.04–0.11 for exothermal reactions and to 0.90–0.96 for endothermal reactions.     

Engineering reactions in crystalline solids: predicting photochemical decarbonylation from calculated thermochemical parameters

A detailed thermochemical analysis of the alpha-cleavage and decarbonylation reactions of acetone and several ketodiesters was carried out with the B3LYP/6-31G* density functional method. The heats of formation of several ground-state ketones and radicals were calculated at 298 K to determine bond dissociation energies (BDE) and radical stabilization energies (RSE) as a function of substituents. Results show that the radical-stabilizing abilities of the ketone substituents play a very important role on the thermodynamics of the alpha-cleavage and decarbonylation steps. An excellent correlation between calculated values and previous experimental observations suggests that photochemical alpha-cleavage and decarbonylation in crystals should be predictable from knowledge of excitation energies and the RSE of the substituent.     

分子内1,3-偶极环加成反应的研究II: 呋喃偶极体系的热及光化学反应

合成并研究了呋喃1,3-偶极C-2-呋喃-N-烯基硝酮(1)的热和光化学反应.1的热化学环加成反应具有区域选择性.生成氧氮杂二环辛烷类化合物.日光灯照明下加热还可得到双键迁移产物.1在波长>302nm下的光化反应产物是氧氮杂环丙烷,而在λ>270nm下除了还有重排产物N-戊烯基-2-呋喃甲酰胺,氧氮杂环丙烷不稳定,加热下通过1发生分子内环加成反应.     

Kinetics and mechanism of photochemical reactions of peroxomonosulfate in the presence and absence of 2-propanol

The photochemical decomposition of peroxomonosulfate (PMS) in the presence and absence of 2-propanol at 25°C was found to obey an overall first-order rate – d[PMS]/dt = k_?[PMS]. In the absence of 2-propanol, the quantum yield ≤ for the decomposition of PMS was found to depend upon the concentration of PMS at [PMS] > 2 × 10^?M, and is independent of concentration at [PMS] > 2 × 10^?2M. The quantum yield in the presence of 2-propanol was found to be 3.03 at [PMS] = 1 × 10^?2M and 4.45 at higher concentrations of PMS. In the pH range of 2–9.0 the quantum yield was found to be independent of pH, and the overall rate constant k_? was found to be 6.49 × 10^?3 s^?1 and 1.68 × 10^?3 s^?1, respectively, in the presence and absence of isopropanol. A suitable chain mechanism is proposed and explained.     

无溶剂条件下N-磺酸琥珀酰亚胺催化乙酰化反应(英文)

A small amount of succinimide-N-sulfonic acid efficiently catalyzed the acetylation of a variety alcohols, phenols, thiols, amines and aldehydes with acetic anhydride at room temperature under solvent free conditions. This catalyst has the advantages of excellent yields and short reaction times and the reaction can be carried out on a large scale, which makes it potentially useful for industrial applications.     

Computational study of the mechanism of the photochemical and thermal ring-opening/closure reactions and solvent dependence in spirooxazines

The spirooxazine/merocyanine couple constitutes a photochromic system that can change from the colorless spirooxazine to the intensely colored merocyanine by thermal or photochemical activation by a reaction that opens the spiro ring of the oxazine. The mechanisms of the ring-opening/closure reactions that interconnect these two isomers have been elucidated by means of a computational study. First, we have used the CASSCF/CASPT2 method to determine in detail these mechanisms in the gas phase for a small model that contains the photoactive part of the whole system. We have found that the state of spirooxazine excited by the initial absorption changes gradually to a lower excited state that is involved in a conical intersection that connects it with the ground state of merocyanine. The same conical intersection is involved in the backward photochemical reaction. Second, using a larger model that includes all the heteroatoms of the system and using the DFT (B3LYP) method, we have studied the influence of a solvent environment on the thermal equilibrium between the open and the closed species. It has been observed experimentally that the thermal equilibrium between these forms is practically unaltered by polar aprotic solvents, but it can be displaced toward the colored form in mixtures of polar protic and aprotic solvents, even if the first one is found in a very small proportion. To reproduce the experimental environments, we have taken into account the long-range effect of the polar aprotic solvent considering it a polarizable continuum, as done in the PCM method, and the short-range effect of the protic solvent including some explicit water molecules in the cluster studied at the atomic level. The results obtained are in good agreement with the experimental observations and explain the reason for this peculiar behavior.     

Study of photopolymers. XVI. Novel syntheses of the polymers with azidonitrobenzoyl groups and their photochemical and thermochemical reactions

Poly-2-(2-azido-5-nitrobenzoyloxy)ethylmethacrylate (P-II-A) and poly-2-(4-azido-3-nitrobenzoyloxy)ethylmethacrylate (P-II-B) were synthesized from the reactions of 2-hydroxyethylmethacrylate with 2-chloro-5-nitrobenzoic acid and 4-chloro-3-nitrobenzoic acid, respectively, by substitution reactions of sodium azide with the corresponding chloronitrobenzoyl group. In addition, the degradation reaction of the 2-azido-5-nitrobenzoyl group in P-II-A and the transformation of the 4-azido-3-nitrobenzoyl group to 5-carboxylbenzofurazane-1-oxide ring in P-II-B by irradiation with ultraviolet (UV) light or by heating were investigated in detail. In the photochemical reaction the reaction of the azide group in P-II-A was affected by the presence of a spacer in the polymer chain. Moreover, in the thermochemical reaction the rates of the reactions of azide groups in P-II-A and P-II-B were controlled by the facility of molecular motion and the conformation of polymer chains.     

Novel photochemical reaction of indole with naphthalene and phenanthrene in the solid state

Irradiation of mixed crystals of indole and naphthalene gave an addition product, 1-(1,4-dihydro-1-naphthyl)indole ( ), while irradiation in solution gave another product in addition to . Similar solid-state photoreaction of indole and phenanthrene gave .     

Diels-Alder reactions between dienamides and quinones: stereochemistry of the cycloadditions and cytotoxic activity of the adducts

Tetrahydronaphthoquinones and tetrahydroanthraquinones bearing an amido group have been prepared by Diels-Alder reactions between (E)-1-(N-carbobenzyloxyamino)-1,3-butadiene (2) or (E)-1-(N-benzoyl-N-benzylamino)-1,3-butadiene (5) and benzoquinone or 5-substituted naphthoquinones. The stereochemistry of the cycloadditions was investigated. A high regioselectivity was observed in the reaction of the diene carbamate 2 with 5-methoxy and 5-acetoxy naphthoquinones. This latter gave the unexpected 1,8-regioisomer 3d. The cycloadditions of the dienamide 5 with naphthoquinones 1 (R = OH, OMe, OAc) are regiospecific. Assignment of the structure of the tetrahydroanthraquinone 6b is in good agreement with the known directing effect of the 5-hydroxy group of juglone 1b in analogous Diels-Alder reactions. With 5-methoxy and 5-acetoxy naphthoquinones, the opposite regiochemistry observed is consistent with the electron-donating influence of the methoxy or acetoxy group, making the C-3 carbon atom more electron deficient. Aromatization of the adducts 6b and 7c was accompanied by an unusual elimination of the amido moiety. Thus, 1-hydroxy and 1-methoxy anthraquinones were obtained. Reactions of the dienes 2 and 5 with benzoquinone gave the tetrahydronaphthoquinones 9 and 10 with an endo stereospecificity. Oxidation of 9 by activated manganese dioxide gave the naphthoquinone 11. These compounds were submitted to in vitro cytotoxic assays towards murine L 1210 leukemia cells and clonogenic human tumor cell line MDA-MB 231. The naphthoquinone derivatives 9, 10 and 11 had significant activities with IC50 less than or equal to 0.4 microgram/ml towards these two tumor cell systems.     

Reactivity of cyclic sulfides in reactions with quinones

Sulfonium salts are obtained by the reaction of cyclic sulfides with 1,4-benzoquinone and 5,8-quinolinedione in an acidic medium. It is shown by the method of concurrent reactions that the introduction of alkyl substituents into molecules of thiacyclopentane and thiacyclohexane decreases the reactivity of the sulfides. Quinolinedione is less reactive towards sulfides than is benzoquinone.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 891–894, July, 1986.     

CASCSF study on the photochemical transposition reactions of pyrazines

Several reaction pathways for the photochemical transformations of methyl-substituted pyrazine in its first excited state 1(pi --> pi*) have been determined using the CASSCF (six-orbital/six-electron active space) and MP2-CAS methods with the 6-311G(d) basis set. Our model investigations suggest that conical intersections play a crucial role in the photoisomerization of pyrazines. Moreover, the present theoretical findings indicate that all of the photoisomerizations of pyrazines adopt the same reaction path as follows: pyrazine --> Franck-Condon region --> conical intersection --> pyrimidine. That is, although an excited-state pyrazine molecule can initiate a phototransposition process easily, this process can be completed on the ground-state potential energy surface after passage through a conical intersection where a fast, radiationless decay is possible. The existence of these nonadiabatic reaction pathways is consistent with the available experimental observations of the photochemistry and photophysics of pyrazine and its methyl derivatives. In the present work, we propose a simple p-pi orbital topology model, which can be used as a diagnostic tool to predict the location of the conical intersections, as well as the geometries of the phototransposition products of various heterocycles.     

Electronic structures of carbazole and indole and the solvent effects on the electronic spectra

The results of the experimental studies on the solvent effects upon the fluorescence and the absorption spectra of carbazole and indole are described, which makes it possible to estimate the difference of the electronic structures in the fluorescence state from those in the ground state.The electronic structures of the molecules are studied theoretically on the basis of the experimental results.

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Zusammenfassung Die Beeinflussung der Absorptions- bzw. Fluoreszenzspektren von Carbazol und Indol durch Lösungsmitteleffekte wird untersucht. Aus den Ergebnissen werden Rückschlüsse auf die Elektronenstrukturen der Grund- und Fluoreszenzzustände gezogen. Eine auf den experimentellen Resultaten basierende theoretische Behandlung der Elektronenstrukturen schließt sich an.

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Résumé Nous avons étudié les effects de solvant sur les spectres d'émission et d'absorption du carbazol et de l'indole. Les résultats permettent des conclusions sur la différence entre les structures électroniques des états excité et fondamental. Des calculs sur ces structures sont faits à l'aide des données expérimentales.

     

An ESR study of photochemical reactions of Co2(CO)6(PBu3)2 with quinones and phenothiazine

The photochemical reactions of Co₂(CO)₆(PBu₃)₂ with various quinones and phenothiazine were studied by ESR. The results indicate that the photolysis of Co₂(CO)₆(PBu₃)₂ in the presence of o-quinones led to the observation of an ESR spectrum, showing a broad 8 or 12 groups of hyperfine lines due to interaction with cobalt (Co, 1 = 7/2). The results show that with o-quinones the cobalt radical adducts are formed via metal chelation to the carbonyl oxygens. However, when Co₂(CO)₆(PBu₃)₂ was irradiated in the presence of p-quinones, only the para-semiquinone radicals were observed. The photolysis of Co₂(CO)₆(PBu₃)₂ with phenothiazine in toluene yields phenothiazine radical. The sixteen and eighteen electrons rule have been used to account for these observations.     

New nucleophilic substitution reactions in the indole series

The direct incorporation of residues of -surplus heterocycles, CH acids, and inorganic anions in the indole ring was accomplished by the reaction of indole with various nucleophilic organic compounds in the presence of acylating agents.See [1] for the preliminary communication.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 493–496, April, 1979.     

The effect of pressure on hydrogen transfer reactions with quinones

The effect of pressure on the oxidation of hydroarenes 3-9 with 2,3-dichloro-5,6-dicyano-1,4-quinone (DDQ; 1 a) or o-chloranil (10), leading to the corresponding arenes, has been investigated. The activation volumes were determined from the pressure dependence of the rate constants of these reactions monitored by on-line UV/Vis spectroscopic measurements in an optical high-pressure cell (up to 3500 bar). The finding that they are highly negative and only moderately dependent on the solvent polarity (DeltaV( not equal ) = -13 to -25 in MTBE and -15 to -29 cm(3) mol(-1) in MeCN/AcOEt, 1:1) rules out the formation of ionic species in the rate-determining step and is good evidence for a hydrogen atom transfer mechanism leading to a pair of radicals in the rate-determining step, as was also suggested by kinetic measurements, studies of kinetic isotope effects, and spin-trapping experiments. The strong pressure dependence of the kinetic deuterium isotope effect for the reaction of 9,10-dihydroanthracene 5/5-9,9,10,10-D(4) with DDQ (1 a) can be attributed to a tunneling component in the hydrogen transfer. In the case of formal 1,3-dienes and enes possessing two vicinal C--H bonds, which have to be cleaved during the dehydrogenation, a pericyclic hydrogen transfer has to considered as one mechanistic alternative. The comparison of the kinetic deuterium isotope effects determined for the oxidation of tetralin 9/9-1,1,4,4-D(4)/9-2,2,3,3-D(4)/9-D(12) either with DDQ (1 a) or with thymoquinone 1 c indicates that the reaction with DDQ (1 a) proceeds in a stepwise manner through hydrogen atom transfer, analogously to the oxidations of 1,4-dihydroarenes, whereas the reaction with thymoquinone 1 c is concerted, following the course of a pericyclic hydrogen transfer. The difference in the mechanistic courses of these two reactions may be explained by the effect of the CN and Cl substituents in 1 a, which stabilize a radical intermediate better than the alkyl groups in 1 c. The mechanistic conclusions are substantiated by DFT calculations.