摘要:

Since the discovery of the electron by Sir Joseph John Thomson a century ago, the limitless applications of the electron in chemistry have been both profound and fun. We present recent results from two of our experiments that involve such applications of the electron beam in the study of new aspects of gas-phase chemical physics and of surface chemistry. In particular, our precise measurements of momentum-transfer-resolved "absolute" excitation transition probabilities of the low-lying transitions in "environment-safe" Freon substitutes using a high-energy electron beam are finding applications in the modelling of low-temperature industrial plasma and atmospheric processes. The use of low-energy electrons as a powerful in situ means to activate and to probe "novel" surface reactions, including oxide and carbide formation and CO oxidation, has been demonstrated on Cu(100) and Si(111) surfaces. These experiments further illustrate the value and the enormous potential of technological payoffs of electron-based fundamental research.Keywords: electron scattering and interactions, surface chemistry.

ISSN:0008-4042    

DOI:10.1139/v97-155

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

A simple model of electron solvation in polar liquids is presented, in which we attempt to link the electron solvation time τsto τ2, the time for reorientation of monomeric molecules, and to τL1, the longitudinal dielectric relaxation time of the solvent. It is shown that this model, which is suggested by the so-called hybrid model of electron solvation previously described for methanol, can satisfactorily account for electron solvation in all polar liquids, including linear alcohols (methanol to decanol), 1,2-ethanediol, H2O, and D2O, for which data are available from the literature. A close similarity is indeed obtained between our calculated values of τsand those measured experimentally. The observation of such a correlation supports a universal concept of electron solvation.Keywords: polar liquids, electron solvation time, solvent dielectric relaxation times, universal concept of electron solvation.

ISSN:0008-4042    

DOI:10.1139/v97-156

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

This paper describes simple and successful methods for the preparation of stabilized halogenated phosphoylides and discusses their stability, reactivity, and utility in organic synthesis. Preparations of several halogenated compounds including pharmaceutically interesting enol lactones are reported.Keywords: halogenated stabilized ylides, preparation, structure, stability, reactivity, applications; vinylic halides, halo enol lactones.

ISSN:0008-4042    

DOI:10.1139/v97-157

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The synthesis of halo enol lactones from cyclic anhydrides via lactonization of the corresponding keto phosphoranes provides a direct route to these interesting compounds, which possess important biological properties and are useful intermediates in organic synthesis. In this paper we outline the syntheses of several halo enol lactones and discuss mechanistic consequences of these reactions on the understanding of Wittig reactions with cyclic anhydrides.Keywords: halolactonization, cyclic anhydrides, halo enol lactones, Wittig reaction mechanism.

ISSN:0008-4042    

DOI:10.1139/v97-158

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Dimethoxycarbene, generated at 110 °C by thermolysis of 2,2-dimethoxy-5,5-dimethyl-Δ3-1,3,4-oxadiazoline, displaces fluoride from aromatic rings that are activated with electron-withdrawing groups. Intermolecular substitution on Sanger's reagent and on hexafluorobenzene are reported, together with intramolecular substitution by a dioxycarbene with a tethered aryl group.Keywords: aromatic substitution, aryl(dimethoxy)fluoromethanes, aryl fluoride, dialkoxycarbene, nucleophilic substitution.

ISSN:0008-4042    

DOI:10.1139/v97-159

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Bromation of 1,10-phenanthroline with Br2proceeds smoothly in the presence of S2Cl2and pyridine to give 3,8-dibromo-1,10-phenanthroline in good yield. Bromation of 2,9-dibutoxy-1,10-phenanthroline with Br2, in an aqueous medium gives 5,6-dibromo-2,9-dibutoxy-1,10-phenanthroline selectively. Similar bromination of 4,7-dibutoxy-1,10-phenanthroline with Br2gives 3,8-dibromo-4,7-dibutoxy-1,10-phenanthroline, which forms a 1:1 adduct with Cu(NO3)2. Molecular structure of the 1:1 adduct has been determined by X-ray crystallography.Keywords: bromination, 1,10-phenanthroline, 3,8-dibromo-1,10-phenanthroline.

ISSN:0008-4042    

DOI:10.1139/v97-160

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The effect of insertion of one 1,4-naphthylene unit into several PEEK-like and Udel®-like commercial polymers is examined. Two series of poly(ether ketone)s and poly(ether sulfone)s were made from the polycondensations of 1-chloro-4-(4-fluorobenzoyl)naphthalene and 1-chloro-4-(4-fluorobenzenesulfonyl)naphthalene with phenolphthalein (PP), 2,2′,6,6′-tetramethyl-4,4′-biphenol (TMBP), and 4,4′-biphenol (BP). Each polymer was soluble in chloroform, from which dense films could be cast. Glass transition temperatures increased 14-19 °C with TMBP, 30–43 °C with BP, and 39–60 °C in the case of PP. The 1,4-naphthylene insertion reduced the crystallinity of the biphenol-based polymers. The onset temperatures for 5% weight loss ranged from 390 to 536 °C in nitrogen, as assessed by thermogravimetry. Young's moduli varied from 0.54 to 2.1 GPa. In the case of the poly (ether ketone) containing TMBP, incorporation of the 1,4-naphthylene moiety increased gas permselectivity at the cost of decreased permeability, whereas there seemed only to be a decrease in permeability with its poly(ether ketone) counterpart.Keywords: naphthalene, poly(ether sulfone)s, poly(ether ketone)s, glass transition temperature, gas permeability.

ISSN:0008-4042    

DOI:10.1139/v97-161

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Two new monomers, 4-chloro-1-(4′-fluoro-1-naphthoyl)naphthalene and 1,4-bis(4′-fluoro-1′-naphthoyl)benzene, have been synthesized and polymerized with four different bisphenols to give two series of the naphthalene-based poly(ether ketone)s that are analogous to commercial PEEK and PEEKK. The effect of the introduction of one or two 1,4-naphthylene moieties, in the backbone of the repeat unit, on the glass transition temperatures has been studied. The glass transition temperatures usually increased by 20–45 °C upon replacing one 1,4-phenylene with one 1,4-naphthylene moiety. All new poly (ether ketone)s prepared in tetramethylene sulfone were amorphous, with the glass transition temperatures in a range of 212–273 °C. The polymer produced from 1,4-bis(4′-fluoro-1′-naphthoyl)benzene and 1,4-hydroquinone in phenyl sulfone as a solvent at 300 °C showed semicrystalline properties with a melting temperature of 310 °C.Keywords: naphthalene, poly(ether ketone)s, synthesis, characterization, glass transition temperature.

ISSN:0008-4042    

DOI:10.1139/v97-162

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Nascent isotactic polypropylene (iPP) has a lower crystallinity and a different X-ray pattern than recrystallized iPP. Heat flows during the melting of nascent highly stereoregular iPP samples are recorded with a Setaram C80 calorimeter over a wideTrange (30–280 °C). The rate of heating–cooling is 1–3 K/h, i.e., much lower than with conventional DSC. Melting is performed after annealing at 30 < Tannealing < 140 °C and with or without substrate. The main peak, that found by DSC, is associated with melting of monoclinic crystals and gives an enthalpy ΔHDSC. Two other peaks, usually above and below the main peak, are observed. These are associated with a slower process of disordering a physical network, which was produced in the sample during polymerization. The sum of ΔHDSCand ΔHnetworkequals ΔHtotal. When melting is complete ΔHtotalis equal to ΔH0, the heat of fusion of perfect iPP crystals. This work presents new information on: (i) the noncrystalline phase of nascent iPP and the heat content of a semicrystalline polymer; (ii) the modifications of the melting process due to strain development, brought about by expansion in the material during the temperature ramp when a physical network is present; and (iii) the effect of a substrate on the polymer melting process.Keywords: nascent iPP, slow calorimetry, strain-melting, change of enthalpy, substrates.

ISSN:0008-4042    

DOI:10.1139/v97-163

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Pt(II) monomeric complexes of N-containing macrocycles have been synthesized and characterized in solution by1H NMR,13C NMR, and electrospray mass spectroscopy (ESMS) and in the solid state by X-ray crystallography. Crystals of [Pt(cyclam)](ClO4)2(cyclam = 1,4,8,11-tetraazacyclotetradecane) are orthorhombic, space groupP21cn,a = 9.596 (3),b = 14.595 (21),c = 24.8782 (20) Å,Z = 8. The structure was solved by direct methods and was refined by the full-matrix least-squares method toR = 0.073 andRw = 0.093 for 2976 reflections withI ≥ 2.5σ(I). Crystals of [Pt(N-methylcyclam)]-(ClO4)2•CH3CN (N-methylcyclam = 1,4,8,11 tetramethyl-1,4,8,11-tetraazacyclotetradecane = NMe4cyclam = tmc) are orthorhombic, space groupPmcn,a = 9.574 (8),b = 14.116 (5),c = 17.5456 (15) Å,Z = 4. The structure was solved by direct methods and was refined by the full-matrix least-squares method toR = 0.067 andRw = 0.091 for 2216 reflections withI ≥ 2.5σ(I). Cyclic voltammetry and EPR spectroscopy have been used to study the redox reactivity of the Pt(II)and Pt(IV) complex ions. The solution chemistry of Pt(IV) complexes based on cyclam andN-methylcyclam was investigated by electrospray mass spectrometry. Electrospray mass spectral evidence has been obtained for the formation of [Pt(III)(cyclam)Cl2]+and [Pt(III)(N-methylcyclam)Cl2]+ions.Keywords: Pt macrocycles, crystallography, electrospray mass spectroscopy, cyclic voltammetry, Pt(III) complex ions, tetraaza macrocycles.

ISSN:0008-4042    

DOI:10.1139/v97-164

出版商:NRC Research Press    

年代:1997

数据来源: NRC