stants of methyl protons and ring protons are quite similar (20-30 gauss), we compare these splittings with those obtained for unsubstituted phenoxy radicals,* (6.6 and 1.9 gauss). The observed splittings from unsubstituted benzosemiquinone2 are all 2.37 gauss, and it seems most probable from this comparison that the r-electron system in 2,3,5,6-tetramethyl-1,4-benzosemiquinone 1-phosphate is that of a phenoxy radical rather than a semiquinone.
ConclusionsThe large isotropic doublet hyperfine splitting observed in the e.s.r. spectra of those semiquinone phosphates which have large groups substituted ortho to the phosphate group is almost certainly due to the P31 nuclear spin. The mechanism of this splitting is most probably due to a hyperconjugation of the phosphate group to the aromatic system, although there is no quantitative evidence for this. Also, the possibility of a conjugation should not be ruled out for the sterically hindered case. The case for steric hindrance of resonance to occur when there is a large doublet splitting appears to be supported by the e.s.r. spectrum of tetramethylbenzoseniiquinone phosphate.
Acknowledgment.The free energies of formation from the constituent binary oxides for each of the following compounds have been measured by means of galvanic cells employing the solid fluorite (written within parentheses) as an electrolyte: CaTi03(CaF2), Ca4Ti3OI0(CaF2), SrTiOa-(SrF3), Sr4Ti3010(SrF2), and MgA1204(MgF2). Zirconia, doped with CaO and MgO, was used as an electrolyte in a galvanic cell to determine the free energies of formation of each of the following compounds a t temperatures from 750 to 1200' : Fe2Ti04, FeTi03, Co2Ti04, CoTi03, NiTi03, FezSiO4, and Ni2Si04. Solid solutions, eutectoids, and peritectoids complicate the interpretation of the e.m.f. measurements at higher temperatures.
Using radioactive tracer Fe‐59 and measuring rest activities after sectioning, the tracer diffusivities of Fe in almost single crystalline magnetite Fe3‐ΔO4 have been measured as a function of temperature and oxygen partial pressure. The measured curves log DFe*/log pO2 all exhibit a minimum in the temperature range between 900°C and 1400°C in the homogeneity range of the magnetite. At sufficiently high oxygen partial pressures the slope ϱ log D Fe*/log pO2 is 2/3: at sufficiently low partial pressures it is —2/3. This allows to conclude that stoichiometric Fe3O4 has a Frenkel disorder in the cationic sublattice, while at high oxygen potentials iron ion vacancies are responsible for the cation deficit. Their electrical charge is balanced by threevalent iron ions.
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