Investigation of the structure and reactivity of the stable perfluorodiisopropylethylmethyl radical by ESR and molecular mechanics

The hyperfine coupling (HFC) constants of the unpaired electron with the fluorine nuclei in the stable radical [(CF₃)₂CF]₂CF₂CF₃ (II) were determined by ESR. The stable conformation and the barriers to rotation of the substituents in this radical were calculated by molecular mechanics. The results were consistent with the ESR data. The kinetics of the destruction of the radical (II) were investigated, and the kinetic parameters of the dissociation were determined (k₁₄₀=4.6·10^–4 sec^–1, E_act=30±5 kcal/mole). The disappearance of the radical (II) is accompanied by the accumulation of the new radical (CF₃)₂CF(CF₃)CF(CF₃)CF₂CF₃ (IV), which was studied by ESR. Heating of (II) in the presence of electron donors leads to the partly reversible reduction of the radical (II).Translated from Izvestiva Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1507–1512, July, 1991.     

α-Oxides in reactions with N-H acids of the heterocyclic series

The reaction of epoxides with 3-nitro-5-bromo-1,2,4-triazole gave a series of 1-(β-hydroxyalkyl)-3-nitro-5-bromo-1,2,4-triazoles, which, under the influence of bases, undergo intramolecular cyclization with HBr elimination to give an ew heterocyclic system — 2-nitro-5,6-dihydrooxazolo[2,3-e]-1,2,4-triazole.     

Redox‐Initiated Radical Polymerisation of Acrylamide in Moderately Frozen Water Solutions

The radical polymerisation of acrylamide initiated with a persulfate/tertiary amine redox pair was performed in liquid (+5 to +35°C) and moderately frozen (–10 to –30°C) aqueous solutions. The reaction in frozen systems resulted in the pronounced increase in the molecular weight of the polymer. The temperature dependence of the yield and molecular weight of cryogenically produced polyacrylamide were of extreme character with a maximum for both parameters in the vicinity of –12.5°C.     

Evolution of the Defect Structure of Zinc-Oxide as a Consequence of Tribophysical Activation

Zinc-oxide powder was tribophysically activated in a high-energy vibro mill in a continual regime in air for 3, 30 and 300 minutes with the purpose of modifying the powders physico-chemical properties. By analyzing of data obtained by X-ray powder diffraction, electron diffraction and transmission electron microscopy, the values of distances between corresponding crystallographic planes, average domain sizes of coherent scattering, i.e. crystallites, width of diffraction lines due to the existence of microstrains, and microstrain values, minimal dislocation densities, dislocation density due to microstrain and real dislocation density, and also average distances between dislocations were determined. The dependence of these values on the activation time was established, which enabled analysis of the evolution of the defect structure of zinc-oxide powders during tribophysical activation by grinding in the described regime.