Photo-oxidation of water by molecular oxygen: isotope exchange and isotope effects

Photolysis of (17,18)O-labeled water in the presence of molecular oxygen is accompanied by transfer of (17)O and (18)O isotopes from water to oxygen, demonstrating that photoinduced oxidation of water does occur. The reaction exhibits the following isotope effect: oxidation of H(2)(17)O is faster by 2.6% (in the Earth's magnetic field) and by 6.0% (in the field 0.5 T) than that of H(2)(18)O. The effect is supposed to arise in the two spin-selective, isotope-sorting reactions-recombination and disproportionation-in the pairs of encountering HO(2) radicals. The former is spin allowed from the singlet state; the latter occurs only in the triplet one. Nuclear spin sorting produced by these reactions proceeds in opposite directions with the dominating contribution of recombination, which provides observable (17)O/(18)O isotope fractionation in favor of magnetic isotope (17)O. Neither isotope exchange nor the reaction itself occurs in the dark.     

Magnetic effects in the oxidation of silicon

The mass spectrometry study has indicated that the magnetic field accelerates the oxidation of the surface of silicon crystals. The oxidation rate also depends on the nuclear spin of silicon: the oxidation rate of atoms with magnetic nuclei (²⁹Si) is almost twice as high as that of atoms with spinless, unmagnetized nuclei (²⁸Si and ³⁰Si). Both effects—magnetic field and magnetic isotope—reliably prove that the oxidation of silicon is a spin-selective reaction involving radicals and radical pairs as intermediate paramagnetic particles. A spin-selective magnetic sensitive oxidation mechanism is discussed.     

Nuclear magnetic resonance spectra under chemical polarization conditions

Russian Chemical Bulletin -     

Effect of nature of substituents in quinobromides on reactions with grignard reagents

Conclusions In reactions with organomagnesium compounds, quinobromides containing electron-acceptor substituents show dual reactivity and in the main undergo dienone-phenol transformations with heterolytic cleavage of the C-Br bond.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1583–1592, July, 1969.We thank N. M. Émanuél for his constant interest in this work.