DSC non-isothermal crystallization curves in polyoxymethylene

Non-isothermal crystallization curves by differential scanning calorimetry for two-dimensional spherulite growth in polyoxymethylene have been modeled using the Avrami equation, taking into account heat dissipation in the sample holder during the phase transition. Good agreement is found for scanning rates up to 40 Kmin^–1 between experimental curves and predictions based on a knowledge of the isothermal crystallization kinetics of the same samples.     

Atomic and solid-state effects in the angle resolved photoemission cross section from an adsorbate: 4d levels of c(2 × 2)Te on Ni

The photon energy dependence of the normal emission from the Te - 4d levels of an ordered Te c(2 × 2) overlayer on Ni(100) shows two distinct types of structure. The main feature is due to an atomic effect, a delayed onset, a peak followed by a Copper minimum. Superimposed on this atomic profile are intensity modulations of 30 to 40% due to coherent scattering from the substrate. The atomic contribution is in qualitative agreement with theoretical calculations, while the modulations due to solid-state effects are not reproduced by a LEED final state type calculation.     

The generation of the diisopropyl nitroxide radical during the reaction of lithium diisopropylamide with α-fluoroacetate esters

The formation of an EPR active species was observed when lithium diisopropylamide (LDA) was employed as the base for deprotonation of fluoroacetates. The EPR of a glass prepared from the reaction mixture showed an intense signal. The solution EPR spectrum of the sample was independent of temperature, and exhibited a hyperfine structure which allowed identification of the radical species as diisopropyl nitroxide. Generation of the enolate by metalation of ethyl fluoroidoacetate gave no evidence for autoxidation occurring in the absence of diisopropylamine.     

Synthesis and characterization of bis(di-2-pyridylmethanamine)ruthenium(II)

The complex Ru(dipa)(2)(2+) (dipa = di-2-pyridylmethanamine) has been prepared, yielding approximately a statistical ratio of the meso and rac isomers. The electronic spectra of both isomers show pyridyl pi --> pi transitions in the UV region and MLCT bands in the visible region. The solvent dependence of the spectra provides evidence of hydrogen bond formation between the solvent and the NH(2) site on the ligand. The electrochemical properties of the two isomers are identical; each undergoes a reversible one-electron oxidation in acetonitrile (E(1/2) = 0.933 V vs Ag/AgCl) and in aqueous solution below pH 3 (E(1/2) = 0.786 V vs Ag/AgCl). In aqueous solution above pH 3, one-electron oxidation of the ruthenium center is followed by deprotonation of the ligand NH(2) site yielding a reactive amidoruthenium(III) species. The ruthenium-bound dipa ligand possesses structural constraints that prevent the usual oxidative dehydrogenation reaction, which would yield exclusively the corresponding imine. Instead the amidoruthenium(III) intermediate finds alternative reaction routes leading to multiple products.