27808-13-5Relevant articles and documents
PHOTOLYSIS OF THE VINYL BROMIDE 9-(α-BROMOBENZYLIDENE)FLUORENE IN METHANOL. EFFECT OF WAVELENGTH OF IRRADIATION, SODIUM METHOXIDE AND OXYGEN.
Verbeek, J. M.,Cornelisse, J.,Lodder, G.
, p. 5679 - 5684 (1986)
A quantitative study of the photosolvolysis of 9-(α-bromobenzylidene)fluorene (1) in methanol reveals that the wavelength of irradiation, the presence of sodium methoxide and the presence of oxygen strongly influence the product distribution and the quantum yields of the reaction.
Photochemical Formation and Electrophilic Reactivities of Vinyl Cations. Influence of Substituents, Anionic Leaving Groups, Solvents, and Excitation Wavelength on Photoheterolysis and Photohomolysis of 1-(p-R-Phenyl)-2-(2,2'-biphenyldiyl)vinyl Halides
Verbeek, Jan-Maarten,Stapper, Marion,Krijnen, Erik S.,Loon, Jan-Dirk van,Lodder, Gerrit,Steenken, Steen
, p. 9526 - 9536 (2007/10/02)
Using product analysis and time-resolved laser flash photolysis techniques, the photochemistry at λexc ca. 250 and 310 nm (exc = excitation) of 1-(p-R-phenyl)-2-(2,2'-biphenyldiyl)vinyl halides (R = H, Me, MeO) in methanol and acetonitrile at room temperature was studied.The title compounds undergo photoheterolysis and photohomolysis to give vinyl cations =C+- (carbenium ions) and vinyl radicals =C.-.The cation : radical ratio increases with electron-donating strength of the substituent R, H - - - -, indicating that the cleavage of the C-X bond to yield cation and halide anion proceeds, in the rate-determining step, by heterolysis and not by homolysis followed by electron transfer in the radical pair.The cation : radical ratio is solvent dependent: e.g., for the vinyl bromide with R = MeO and with λexc = 308 nm, in CH2Cl2 as solvent, only radical is observed, in comparison with only cation in the much more polar solvent acetonitrile.In acetonitrile-methanol mixtures, the absolute yields of both cation and radical go through a maximum as the methanol content is increased, however, the catio : radical ratio decreases continuously with increasing .For a particular R, the quantum yield for C-X bond cleavage is higher at ca. 250 than at ca. 310 nm.Also, the cation : radical ratio is wavelength-dependent: at λexc ca. 310 nm there is relatively more heterolysis than at λexc ca. 250 nm.Rate constants for reaction of the cations with nucleophiles were determined in acetonitrile.Those for reaction of the cation with R = MeO (lifetime in acetonitrile 7 μs) with anionic nucleophiles such as the halides are at the diffusion limit in this solvent, ca. 2 * 1010 M-1 s-1, whereas those for reaction with water, alcohols, and cyclic ethers are of the order 105-106 M-1 s-1.The less stabilized cation (R = Me) reacts with alcohols faster by the factor ca. 100, and it decays in acetonitrile ca. 100 times more rapidly.Also, 1-(p-R-phenyl)-2-dimehtylvinyl bromides (R = H, Me, MeO) were photolyzed in acetonitrile.In the case of R = MeO, the cation p-CH3O-C6H4-C+=CMe2 was seen (lifetime 770 ns), and its reactivity with alcohols (k values of 106-107 M-1 s-1) and halides (k values of 1010 M-1 s-1) was determined.The vinyl radicals =C.- react with O2 to yield vinylperoxyl radicals =C-O2. which have absorption maxima at ca. 390 nm.
