Charge-transfer absorption of olefins with nitrosonium. Structural relevance to the dimethylbutene complex with dinitrogen tetraoxide

The transient electron donor-acceptor (EDA) complexes of various olefins (dimethylbutene, etc.) with the nitrosonium acceptor (NO⁺) show diagnostic charge-transfer absorption bands in dichloromethane solutions at low temperatures. Since the same charge-transfer absorption bands are observed when olefins are exposed to dinitrogen tetraoxide, they are ascribed to analogous EDA complexes [olefin, NO⁺] NO₃ ^? that are derived from the ionic disproportionation of nitrogen dioxide.     

Pd-catalyzed copolymerization of methyl acrylate with carbon monoxide: structures, properties and mechanistic aspects toward ligand design

Full details are provided for the alternating copolymerization of acrylic esters with carbon monoxide (CO) catalyzed by palladium species bearing a phosphine-sulfonate bidentate ligand. The copolymer of methyl acrylate (MA) and CO had complete regioregularity with stereocenters that slowly epimerize in the presence of methanol. In the presence of ethylene, terpolymers of MA/ethylene/CO were also prepared. The glass transition temperatures of the co- and terpolymers were higher than that of the ethylene/CO copolymer. Both experimental and theoretical investigations were performed to clarify the superior nature of the palladium phosphine-sulfonate system compared to an unsuccessful conventional palladium diphosphine system: (i) The reversible insertion of CO was directly observed with the isolated alkylpalladium complexes, [{o-((o-MeOC(6)H(4))(2)P)C(6)H(4)SO(3)}PdCH(CO(2)Me)CH(2)COMe], whereas it was not observed with the corresponding complex bearing 1,2-bis(diphenylphosphino)ethane (DPPE). (ii) The transition state of the subsequent MA insertion, the rate-determining step of the catalytic cycle, was lower in energy in the phosphine-sulfonate system than in the DPPE system. This stabilization could be attributed to the less hindered sulfonate moiety as well as the stronger back-donation from palladium to the electron-deficient olefin, which is located trans to the sulfonate.     

Iron catalysis of grignard reductions. Mechanism of 1, 3-reductive eliminations from γ-propyl halides

The iron-catalyzed reduction of various 3-substituted propyl bromides by Grignard reagents affords propylene and cyclopropane. The reduction to propylene is particularly noteworthy since it formally represents a 1, 2-hydrogen shift. Two key intermediates have been identified in propylene formation, in which 3-methoxypropyl bromide is first catalytically reduced to the magnesium derivative by Grignard reagent. The iron-catalyzed β-elimination of the 3-methoxypropylmagnesium intermediate affords allyl methyl ether, which is then reduction cleaved to propylene. Extensive studies of deuterium labeling in the reactants, as well as in both intermediates, allow the course of the hydrogen shift to be followed unequivocally. The mechanism of iron catalysis is proposed in Scheme 2 and 3, representing the first and second stages of the reduction to propylene.     

Beta-delayed proton emitter kr

The nucleide ⁷³Kr has been identified by on-line mass separation as a precursor of β-delayed proton emission. The proton branch is (6.8 ±1.2) × 10⁻³ proton/decay. The protons populate the ground state and also the first excited 2⁺ state at 866 keV in ⁷²Se with a relative intensity of (35±9) %. The value of Q_EC−B_p, where B_p is the proton separation energy for the nucleus ⁷³Br, is found to be 4.85 ±0.30 MeV based on the fraction of proton events preceded by positron decay.     

Molecular aggregation of solid aromatic polymers. III. Small-angle X-ray scattering from aromatic polyamideimide film

Molecular aggregation in polytrimellitamideimide (PAI) was investigated by small-angle x-ray scattering (SAXS). PAI films annealed above the glass transition temperature show a scattering peak characteristic of two-phase structure. A one-dimensional model was used to analyze these SAXS curves. The more ordered phases are produced at higher annealing temperature. The average thickness of the ordered lamellae is comparable with the repeating length of the main chain. The relative difference of electron density between two phases is only a few percent, which shows that the two-phase structure of PAI, like that of aromatic polyimide, differs essentially from that of ordinary crystalline polymers.     

Application of environmental relaxation model to the transport behavior of glass-forming melts

The environmental relaxation model was applied successfully to explain the temperature dependence of viscosity, conductance, and the Walden product of molten Ca(NO₃)₂.3.91H₂O + NiCl₂ system in the non-Arrhenius region. This model was applied to pure melts, binary molten salt systems with ideal solutions marked by the absence of complex ions, and systems in which octahedral or tetrahedral complexes are formed. The values of the glass transition temperature obtained from the free volume and environmental relaxation models are in good agreement. The values of apparent activation energies for viscous and conductance flows derived from these two models are also comparable.