Nonisothermal kinetic analysis of the chemiluminescence from tetramethyl-1,2-dioxetane

A computerized method is given for the evaluation of Arrhenius parameters which describe the chemiluminescent decomposition of tetramethyl-1,2-dioxetane. The parameters were determined in several solvents by linear regression methods and the equation ln ln \documentclass{article}\pagestyle{empty}\begin{document}$ [(\sum\nolimits_0^\infty I - \sum\nolimits_0^t I)/(\sum\nolimits_0^\infty I - \sum\nolimits_0^t I - \sum\nolimits_0^{t + \Delta t} I)] = \ln\, (A_1 \Delta t) - E_1 /RT$\end{document}, where I refers to photons counted by increments of Δt, and E₁ and A are the first-order Arrhenius parameters. The average of E₁ and log A₁ (s^?1) from this method from six runs in CCl₄ with initial concentrations of 4.9 × 10^?5-8.45 × 10^?4M were 27.21 ± 0.88 kcal/mol (113.7 ± 3.7 kJ/mol) and 13.88 ± 0.50, respectively. Simulated curves of chemiluminescence versus time were obtained with the use of a computer program and an auxiliary plotter.     

Holographic vibration study of a rotating propeller blade

Holographic interferometry has often been used to determine the natural frequencies and the associated mode patterns of vibrating objects with rigidly fixed or stationary boundaries. This paper describes a new pulse-laser holographic technique whereby the vibration-mode patterns of a rotating propeller blade were determined. This technique consists of rotating the holographic plate on the same axis as the rotating object and using spherically symmetric wavefronts for object and reference beams.     

Mechanisms of reaction of aminoxyl (nitroxide), iminoxyl, and imidoxyl radicals with alkenes and evidence that in the presence of lead tetraacetate, N-hydroxyphthalimide reacts with alkenes by both radical and nonradical mechanisms

1,2-dideuterio-cyclohexene, 1,2-dideuterio-cyclooctene, and trans-3,4-dideuterio-hex-3-ene were reacted with three >NO* radicals: 4-hydroxyTempo, di-tert-butyliminoxyl, both used as the actual radicals, and phthalimide-N-oxyl (PINO) generated from N-hydroxyphthalimide (NHPI) by its reaction with tert-alkoxyl radicals (t-RO*) and with lead tetraacetate. In all cases, except the NHPI/Pb(OAc)4 system, only mono >NO-substituted alkenes were produced. The 2H NMR spectra imply that 88-92% of monoadducts were formed by the initial abstraction of an allylic H-atom, followed by capture of the allylic radical by a second >NO*, while the remaining 12-8% appear to be formed by an initial addition of >NO* to the double bond followed by H-atom abstraction by a second >NO*. A substantial and sometimes the major product formed with the NHPI/Pb(OAc)4 system has two PINO moieties added across the double bond. Since such diadducts are not formed with the NHPI/t-RO* system, a heterolytic mechanism is proposed, analogous to that known for the Pb(OAc)4-induced acetoxylation of alkenes. A detailed analysis of the NHPI/Pb(OAc)4/alkene products indicates that monosubstitution occurs by both homolytic and heterolytic processes.     

Determination of the axial-vector weak coupling constant with ultracold neutrons

A precise measurement of the neutron decay β asymmetry A? has been carried out using polarized ultracold neutrons from the pulsed spallation ultracold neutron source at the Los Alamos Neutron Science Center. Combining data obtained in 2008 and 2009, we report A? = -0.119?66±0.000?89{-0.001?40}{+0.001?23}, from which we determine the ratio of the axial-vector to vector weak coupling of the nucleon g{A}/g{V}=-1.275?90{-0.004?45}{+0.004?09}.     

Deuterium isotope cage effects in the dismutation of alkoxyl radicals. Significance for the mode of alkylperoxyl termination

Decomposition of (R₁R₂CXON=)₂ (R₁ = R₂ = Ph; R₁ = R₂ = p? ClC₆H₄; R₁ = Ph, R₂ = CH₃; X = H or D) in hydrocarbon solvents at 31–75°C afforded R₁R₂CO in 6–8% lower yield when X = D than when X = H. This result is ascribed to cage escape of secondary alkoxyl radicals in competition with dismutation. Deuterium isotope effects for alkoxyl cage dismutation of 1.35–2.4 are estimated from the data. It is suggested that this same competition may account for the experimentally slower termination rate constants in solution of primary and secondary alkylperoxyl radicals on α-deuteration.     

Chemistry of the phenoxathiins and isosterically related heterocycles. XXX. The crystal and molecular structure of 2-AZA-phenoxathiin 2-oxide: Further evidence in support of the relationship between the 13C-NMR chemical shift of C-10a resonance and the molecular dihedral angle

The synthesis of 2-azaphenoxathiin 2-oxide ( 4 ) and the total assignment of the ¹³C-nmr spectrum is described. Facile assignment was obtained from the assigned spectrum of 2-azaphenoxathiin with additivities obtained from a comparison of 1-azaphenoxathiin and its N-oxide. The crystal structure has also been determined from three dimensional X-ray diffraction data. The compound crystallizes in the monoclinic space group P2₁/n with a = 17.50(2)Å, b = 7.147(3)Å, c = 16.044(7)Å, β = 110.60(5) and Z = 8. Intensity data were collected at - 135 ± 2°C on an automatic diffractometer using nickel-filtered CuKα radiation. The structure was solved by direct methods and was refined by least-squares techniques to give a final R-value of 0.045 for all 3831 independent reflections.