On the origin of cis selectivity in the cyclization of N-protected 2-substituted 3-aza-5-hexenyl radicals: a density functional study

Cyclization of the N-dimethylphosphinoyl-2-methyl-3-aza-5-hexenyl radical has been studied at the UB3LYP/6-31+G(d)//UB3LYP/6-31G(d) hybrid density functional level. The corresponding radical precursor has been synthesized and found to give cis/trans ratios of up to 10/1 in reductive radical cyclizations. The relative energies of reactant and transition state conformers were determined. In discord with the Beckwith-Houk model, it has been found that chair-axial transition states, which lead to cis products, are lowest in energy, rationalizing the observed experimental diastereoselectivity.     

Experimental Critical-Exponent Values for Fluids

After a review of the history and an assessment of the current status of the subject, we present light-scattering data to determine the critical correlation-function exponents for an aqueous electrolyte solution yielding the experimental values γ=1.238±0.012, ν=0.629±0.003, η=0.032±0.013. We conclude the paper with some comments concerning the temperature dependence of non-asymptotic effective critical-exponent values of fluids.     

有机橡胶助剂的全分析

橡胶产品中橡胶助剂的分析有重要现实意义。由于橡胶产品中添加的助剂种类较多,添加量差别较大,部分助剂又已发生反应,因此进行橡胶助剂的全分析是一项有较高难度的工作。通过中压色谱分离,红外光谱定性的方法,鉴定了乙丙橡胶助剂中的矿物油、邻苯二甲酸酯、植物油等3种软化剂,以及残余的硫化促进剂M和防老化剂苯乙烯化苯酚; 采用固相萃取去除助剂中主量成分矿物油,以减少对其他少量助剂成分的干扰,通过气质联用法,推测出橡胶助剂中的2,6-二叔丁基-4-甲基苯酚防老剂、残余的秋兰姆类硫化促进剂,同时利用气质联用仪,直接测定乙丙橡胶抽提液,鉴定了残余的活泼性物质过氧化苯甲酰类硫化剂。文章研究结果可供其他橡胶体系有机助剂全分析的借鉴。     

TIME-TEMPERATURE-MISCIBILITY AND MORPHOLOGY OF POLYOLEFIN BLENDS

Miscibility and crystallization have been studied for polypropylene-polyethylene and polyethylene-polyethyleneblends. In the case of the polypropylene blends the composition of interest is 20% polypropylene. At this composition thepolypropylene has been found to be soluble in linear low density polyethylene but insoluble in high, low and very lowdensity polyethylenes. The miscibility has been concluded from the crystallization kinetics and polarised optical microscopywith a hot stage. Polyethylene-polyethylene blends have been formed from polymers with similar average branching contentbut where they have different melting temperatures. Important consequences are to introduce long branches into apolyethylene that only has short branches, and to modify the morphology of a polyethylenes so that haze, gloss and strainhardening are improved. Polyethylene blends must be developed after careful consideration of the branch content anddistribution within each of the constituents. It is not sufficient to simply blend polyethylenes, with the desired range ofproperties, without regard to the miscibility of the blend composition.     

Two dimensional Kohn anomally in NbSe2

Phonon dispersion curves for several low frequency branches in the layered compound NbSe₂ have been measured. The results indicate the possible existence of a two dimensional Kohn anomaly in this material.     

Enhancement of the superconducting transition temperature near a phase instability in NaxWO3

The superconducting transition temperature of tetragonal I sodium tungsten bronze (Na_xWO₃) has been found to increase rapidly as the x-value is decreased to the metal-semiconductor phase transition. It is suggested that a soft mode instability is responsible for the increased electron-phonon interaction near the phase transition.     

Level structures of 95,97Mo — A comparative study

High-spin states of ^95,97Mo (Z=42, N=53,55) nuclei have been investigated through ⁸²Se(¹⁸O, xn) reaction at Eb=60 MeV. The level scheme in ⁹⁵Mo has been observed upto ≏ 10 MeV in the present experiment. The level structure shows mainly single particle character. In ⁹⁷Mo, the ground state level sequence has been extended to ≏ 4.5 MeV while the previous information had been up to 2.4 MeV. A negative parity band built on 1437 keV (11/2⁻) excited state has been extended to 5.5 MeV. The structure seems to show a coexistence of single particle and collective modes of excitation. Properties of both the nuclei have been compared with shell model calculations using OXBASH.     

High spin rotational bands in 65Zn

The nucleus ₃₀ ⁶⁵ Zn was studied using the ⁵²Cr(¹⁶O, 2pn)⁶⁵Zn reaction at a beam energy of 65 MeV. The level scheme is extended up to an excitation energy of 10.57 MeV for spin-parity (41/2?) with several newly observed transitions placed in it.