67175-53-5Relevant academic research and scientific papers
Spectroscopy and photochemistry of a series of alkyl-substituted o- and p-benzoquinones and their mono-oxime O-methyl ethers
Stunnenberg, Frank,Cerfontain, Hans,Rexwinkel, Roel B.
, p. 438 - 447 (2007/10/02)
Following our previous reports on the spectroscopy and photochemistry of methyl ethers of cyclic α-oxo oximes, we have now studied a number of o- and p-benzoquinone mono-oxime O-methyl ethers and, for comparison, some corresponding o- and p-benzoquinones.The ground-state electronic structure of o-benzoquinones is described satisfactorily by the sum of the two propenal fragments.The structure of the corresponding (E)- and (Z)-mono-oxime ethers can be described similarly as the sum of the propenal and (E)- or (Z)-(methoxyimino)propene fragments.This method fails whenused for the construction of the ground-state electronic structure of the isomeric p-benzoquinones and their mono-oxime ethers.The UV spectra of o-benzoquinone mono-oxime ethers are quite different from those of the parent o-benzoquinones in that the free lying n+?* absorption of the latter is, for the former, shifted to lower wavelength and apparently hidden under the long-wavelength ??* absorptions.For the p-benzoquinone mono-oxxime O-methyl ether 12, however, the long-wavelength n?* absorption remains visible.Direct irradiation of the tert-butyl-substituted o-benzoquinone mono-oxime O-methyl ethers (E)-5 - (E)-7 dissolved in acetonitrile at λ 350 nm leads (in addition to E-Z isomerization) to the formation of the (E)-azobenzenes 16-19 by dimerization of the respective phenylnitrenes.However, in addition, the 2,4-di-tert-butyl derivative (E)-7 undergoes mainly γ-hydrogen abstraction, probably from the S1(n?*) state, leading to subsequent cyclization to the relatively stable dienol (E)-14, which eventually isomerizes thermally to the enone (E)-15.Evidence is presented that (Z)-7 exhibits only Z-E photoisomerization and no photocyclization, as has been observed previously with the saturated six-membered ring analogue.Direct irradiation of the corresponding 3,5-di-tert-butyl-o-benzoquinone (3) at 350 nm leads to decarbonylation with formation of cyclopentadienone 13.Sensitized irradiation of mono-oxime O-methyl ether (E)-7, using 1-acetylnaphthalene and 1-fluorenone as triplet sensitizers and acetonitrile as solvent, leads to E-Z isomerization only with eventual photostationary state / ratios of 0.78 and 0.88, respectively.The p-benzoquinone mono-oxime O-methyl ethers 11 and 12 are photostable against 254, 300 and 350 nm radiation; however, any occuring E-Z isomerization escapes detection for symmetry arguments.
Photolysis of N-Alkoxybenzoquinone Imine N-Oxides
Baldry, Peter J.,Forrester, Alexander R.,Ogilvy, Munro M.,Thomson, Ronald H.
, p. 2035 - 2040 (2007/10/02)
Photolyses of a series of N-alkoxybenzoquinone imine N.oxides give products arising mainly from alkyl radicals, the solvent, and the several quinonoid species present in the reaction mixture.The alkyl radicals may be derived by fragmentation of the corresponding alkoxynitrenes which also rearrange to nitroso-compounds and hence to oximes.
