Hydrogen photochemistry

With other ring sizes, the photochemistry of cyclic enones may take different courses. For cyclopentenones, the principal products result from hydrogen abstraction processes. Irradiation of cyclopentenone in eyclohexane gives a mixture of 2- and 3-cyclohexyleyclopentanone. These products can be formed by intermolecular hydrogen abstraction, followed by recombination of the resulting radicals ... 

His researches and those of his pupils led to his formulation in the twenties of the concept of active catalytic centers and the heterogeneity of catalytic and adsorptive surfaces. His catalytic studies were supplemented by researches carried out simultaneously on kinetics of homogeneous gas reactions and photochemistry. The thirties saw Hugh Taylor utilizing more and more of the techniques developed by physicists. Thermal conductivity for ortho-para hydrogen analysis resulted in his use of these species for surface characterization. The discovery of deuterium prompted him to set up production of this isotope by electrolysis on a large scale of several cubic centimeters. This gave him and others a supply of this valuable tracer for catalytic studies. For analysis he invoked not only thermal conductivity, but infrared spectroscopy and mass spectrometry. To ex-... 

Benzoin and a wide variety of related compounds (e.g. 12, 70-74) have been extensively studied both as initiators of polymerization and in terms of their general photochemistry.271 2 3 The acetophenone chromophore absorbs in the near UV (300-400 nm). In the absence of hydrogen atom donors the mechanism of... 

Both reactions are known from photochemistry and mass spectrometry. Enhancement of the hydrogen yield by electrostatic fields therefore cannot be used to argue against Reaction 2. 

In many cases the transformations may be more complex than indicated by Eqs. (9.89)-(9.100). An example of this is the photochemistry of cis,cis-1,3-cyclooctadiene [Eq. (9.94)].<169) A close examination of this reaction indicates that bicyclo[4.2.0]oct-7-ene is formed but in low relative yields during the initial reaction (see Table 9.9). In addition, the cis,trans-1,3-cyclooctadiene is formed and then consumed as the reaction proceeds. Fonken showed that the bicyclooctene initially formed, however, was not from thermal isomerization of the cis,trans-diene. Still a third reaction was the 1,3 sigmatropic hydrogen shift to form the cis, cis-1,4-cyclooctadiene ... 

Tram-anular interactions, which would create an active radical site via hydrogen transfer through 98, cannot be invoked to explain the specific loss of a CH3 radical from the ether side chain. This conclusions is based upon the following experimental observations. The radical cation of the tetrafluoro substituted compound 101 eliminates CH3, but loss of CH3 from the para-isomer 102 is not observed. If a transanuiar process according to 97- 98 were operative, then such a reaction is not expected to be suppressed upon substitution of H by F as is known for many examples from the field of photochemistry of fluoro substituted compounds41 (23). 

Kohno, Y., Hayashi, H., Takenaka, S., Tanaka, T., Funabiki, T. and Yoshida, S. Photo-enhanced reduction of carbon dioxide with hydrogen over Rh/Ti02. Journal of Photochemistry and Photobiology. 1999. A 126,117-123. 

T., and Haruta, M. (1995) Photoassisted hydrogen production from a water-efhanol solution a comparison of activities of Au-TiOj and Pt-Ti02. Journal of Photochemistry and Photobiology A Chemistry, 89 (2), 177-189. 

Bard, A.J. and Fox, M.A. (1995) Artificial photosynthesis solar splitting of water to hydrogen and oxygen. Accounts of Chemical Research, 28 (3), 141—145. Imahori, H., Mori, Y., and Matano, Y. (2003) Nanostructured artificial photosynthesis. Journal of Photochemistry and Photobiology C Photochemistry Reviews, 4 (1), 51-83. 

P. J. Wagner, B. -S. Park, Photoinduced Hydrogen Atom Abstraction by Carbonyl Compounds, in Organic Photochemistry, Vol. 11. A. Padwa (ed.), Marcel Dekker, New York, 1991, pp. 227-365 and references therein. 

Aromatic substitution, a quantitative treatment of directive effects in, 1, 35 Aromatic substitution reactions, hydrogen isotope effects in, 2, 163 Aromatic systems, planar and non-planar, 1, 203 Aryl halides and related compounds, photochemistry of, 20, 191 Arynes, mechanisms of formation and reactions at high temperatures, 6, I A-Se2 reactions, developments in the study of, 6,63... 

Although this reaction appears to involve only two electrons, it was shown by Mulder [57] that in fact two n and two a electrons are required to account for this system. The three possible spin pairings become clear when it is realized that a pair of carbene radicals are formally involved, Figure 14. In practice, the conical intersection defined by the loop in Figure 14 is high-lying, so that often other conical intersections are more important in ethylene photochemistry. Hydrogen-atom shift products are observed [58]. This topic is further detailed in Section VI. 

Dilling, W.L., Gonsior, S.J., Boggs, G.U., Mendoza, C.G. (1988) Organic photochemistry. 20. A method for estimating gas-phase rate for reactions of hydroxyl radicals with organic compounds from their relative rates of reaction with hydrogen peroxide under photolysis in 1,1,2-trichlorotrifluoroethane solution. Environ. Sci. Technol. 22, 1447-1453. 

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