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971.
Samarium chloride and borohydride complexes of the diamide-diamine ligands (2-C5H4N)CH2N(CH2CH2NR)2(R = SiMe3 or mesityl) are described; the borohydride compounds are the first polydentate amide-supported single component lanthanide catalysts for the controlled polymerisation of polar monomers, and also represent the first lanthanide borohydride complex for the polymerisation of methyl methacrylate.  相似文献   
972.
The syntheses of three decalin-based tert-thiols displaying varying degrees of solubility in aqueous milieu are described. The S-nitroso derivatives of these compounds have also been prepared and the structures of two of these determined by single crystal X-ray diffraction. These compounds have been designed for studying the interaction of nitric oxide (NO) with thiols under physiological conditions.  相似文献   
973.
The 2002 revision of the UV index (UVI) issued by the World Health Organisation (WHO), the World Meteorological Office (WMO), the United Nations Environment Programme (UNEP) and the International Commission on Non-Ionizing Radiation Protection (ICNIRP) (World Health Organization [2002] Global Solar UV Index: A Practical Guide. WHO, Geneva) was motivated by the need to further standardize the use and presentation of the UVI. Awareness of the hazards of solar UV radiation (UVR) is generally high in Australia, but more effective use of the UVI will assist in promoting further changes to the population's sun exposure behavior. UVI levels for a number of cities around Australia as measured by the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA), covering the time period 1996-2000, are presented. Also shown are UVI forecasts from the Australian Bureau of Meteorology (BOM). Agreement between the BOM data and the measurements varies depending on the location but is within 2 UVI units approximately 75% of the time. UVI levels are supplied to the media, and in summer values in excess of 12-14 are regularly recorded, although the more northerly locations occasionally reach 16 and 17. The factors affecting the solar UVR environment and the measured UVI are also discussed and compared against measurements from the UK.  相似文献   
974.
The single crystal x-ray structures of (E)-(2-arylethenyl)cyclooctatetraenes 1 and 2 have been determined. The nitro group in 2 does not influence the geometry of the COT ring relative to that of 1. The influence of various substituents on several structural parameters of the COT ring are analyzed in terms of steric/electrostatic and electronegativity effects of the substituent.  相似文献   
975.
The SLOWPOKE nuclear reactor meets many modern elemental analysis requirements; rapid multielement analysis of most types of samples is possible. The variable neutron flux (maximum 1012 n cm-2 s-1) is stable, homogeneous and reproducible from day to day over a period of months. Sensitivities for 78 elements analyzed by neutron activation, with short irradiation and counting periods, have been determined; the conditions allow rapid multielement analysis with short sample turn-round time. Examples of the application of the technique to complex practical samples are given.  相似文献   
976.
An application of surface-enhanced Raman spectroscopy (SERS) to evaluating the kinetics of electrochemical reactions is outlined. This involves monitoring the potential-dependent SERS intensities of the adsorbed reactant at a rotating disk electrode in a potential region where the kinetics are under mixed mass transfer-heterogeneous electron transfer control. Comparisons are made between the kinetic behavior extracted from the SERS intensity-potential dependence and that obtained from the faradaic current flow. For Co(NH3)63+ reduction at silver, where the reactant is electrostatically attracted but not bound to the surface, the SERS and electrochemical rate behavior is closely compatible. However, for Cr(NH3)5Br2+ and Cr(NH3)5NCS2+ reduction, where the reactants bind directly to the surface prior to electron transfer, the reactivities at the SERS-active sites are substantially higher than for the prevalent adsorbate as obtained electrochemically. These findings suggest that surface sites displaying efficient Raman scattering may also provide centers of catalytic activity.  相似文献   
977.
The imidotungsten dimethyl compound [W(N2Npy)(NPh)Me2] 2 reacts with BArF3 to form the cationic complex [W(N2Npy)(NPh)Me]+ 3+ [anion = [MeBArF3]-; ArF = C6F5; N2Npy = MeC(2C5H4N)(CH2NSiMe3)2] which undergoes methyl group exchange with added 2, [Cp2ZrMe2] or ZnMe2; treatment of cation 3+ with CO2 or isocyanates leads to cycloaddition reactions at the W=NPh bond and not insertion into the W-Me bond, despite the latter product being the most thermodynamically favourable according to DFT calculations.  相似文献   
978.
The direct fluorination of intimately mixed niobium and tantalum powders gives a range of mixed‐metal pentafluorides [NbxTa4‐xF20] (x = 1 2 , 2 3 , 3 4 ) as discreet species isostructural with tantalum pentafluoride (x = 0 1 ). The crystal structures of 1–4 are indistinguishable by X‐ray crystallography. Complex 1 crystallizes in the monoclinic space group C2/m with a = 9.5462(13), b = 14.3578(19), c = 5.0174(7) Å, β = 97.086(2)°, Z = 2. The geometry about the tantalum atom is distorted octahedral with 2 short and 2 slightly longer Ta‐Fterminal, and 2 Ta‐Fbridging distances. The angles at the bridging fluorine atoms are 172.9(5)°.  相似文献   
979.
Reactions of the lithiated diamido-pyridine or diamido-amine ligands Li(2)N(2)N(py) or Li(2)N(2)N(am) with [W(NAr)Cl(4)(THF)] (Ar = Ph or 2,6-C(6)H(3)Me(2); THF = tetrahydrofuran) afforded the corresponding imido-dichloride complexes [W(NAr)(N(2)N(py))Cl(2)] (R = Ph, 1, or 2,6-C(6)H(3)Me(2), 2) or [W(NAr)(N(2)N(am))Cl(2)] (R = Ph, 3, or 2,6-C(6)H(3)Me(2), 4), respectively, where N(2)N(py) = MeC(2-C(5)H(4)N)(CH(2)NSiMe(3))(2) and N(2)N(am) = Me(3)SiN(CH(2)CH(2)NSiMe(3))(2). Subsequent reactions of 1 with MeMgBr or PhMgCl afforded the dimethyl or diphenyl complexes [W(NPh)(N(2)N(py))R(2)] (R = Me, 5, or Ph, 6), respectively, which have both been characterized by single crystal X-ray diffraction. Reactions of Li(2)N(2)N(py) or Li(2)N(2)N(am) with [Mo(NR)(2)Cl(2)(DME)] (R = (t)Bu or Ph; DME = 1,2-dimethoxyethane) afforded the corresponding bis(imido) complexes [Mo(NR)(2)(N(2)N(py))] (R = (t)Bu, 7, or Ph, 8) and [Mo(N(t)Bu)(2)(N(2)N(am))] (9).  相似文献   
980.
Aryl carboxamides are useful structural units found in several biologically active compounds. Unlike their benzoic acid counterparts, fluorinated versions of naphthoic acids are relatively unknown. In connection with a recent project, we needed viable syntheses of several mono- and difluorinated naphthoic acids. Herein we describe the synthesis of 5-, 6-, 7-, and 8-fluoro-1-naphthalenecarboxylic acids and 5,7-, 5,8-, 6,7-, and 4,5-difluoro-1-naphthalenecarboxylic acids. The 5-fluoro derivative 1was obtained from the corresponding 5-bromo compound via electrophilic fluorination of the lithio-intermediate. The rest of the monofluoro (2, 3, and 4) and the difluoro acids (5, 6, and 7) were prepared by a new, general route which entailed the elaboration of commercial fluorinated phenylacetic acids to 2-(fluoroaryl)glutaric acids with differential ester groups; selective hydrolysis to a mono acid, intramolecular Friedel-Crafts cyclization, and aromatization furnished the target structures. An alternative process to assemble a naphthalene skeleton is also presented for the difluoro acids 5 and 6. Finally, 4,5-difluoro-1-naphthalenecarboxylic acid (8) was prepared expeditiously from 1,8-diaminonaphthalene by adapting classical reactions.  相似文献   
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