摘要:

AbstractWe describe the design and construction of a high‐resolution pulsed field‐gradient NMR probe for use in a high‐field superconducting magnet. Overview and details of the design and construction of the probe case, rf circuitry, temperature control and shielded gradient coils for a heteronuclear probe suitable for a spectrometer (Bruker MSL‐300) equipped with a wide bore (i.e., 89 mm) magnet (Oxford) are given. The interior of the probe is designed so mat it may be easily moved to variable height so as to accept easily various gradient coils. A design for a novel jig for the winding of saddle‐geometry rf coils

ISSN:0009-4536    

DOI:10.1002/jccs.199400016

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractAddition of functionalized zinc‐copper reagents to the title complexes proceeds in a highly diastereoselective fashion to afford dienol complexes. The relative configurations of adducts3dwere determined by single X‐ray diffraction analy

ISSN:0009-4536    

DOI:10.1002/jccs.199400017

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractUtilisation of a miniature anion‐exchanger preconcentration column of Dowex 1‐X8 to increase the sensitivity for As and Se determinations by inductively‐coupled‐plasma mass spectrometry (ICP‐MS) is described. The ion signal was enhanced were 15 fold for As and 20 fold for Se. The multielement detection limits were 2 ppt (ng/L) and 33 ppt for As and Se, respectively. This flow injection ICP‐MS method was applied to the determination of trace levels of arsenic and selenium in riverine reference material SLRS‐2 and spring

ISSN:0009-4536    

DOI:10.1002/jccs.199400018

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe conversion of 1,2,4‐trimethy]benzene (1,2,4‐TMB) over HY zeolite was studied at atmosoheric pressure and 200–300 °C by using a fixed‐bed, integral‐flow reactor. The types and initial selectivities of various products were obtained from plots of product selectivity according to the time‐on‐stream theory. The primary reaction included the isomerization and the disproportionation; the former led to the simultaneous formation of 1,2.3‐ and 1,3,5‐TMB whereas the latter produced all isomers of xylene and tetramethylbenzene. The relative initial rate of disproportionation to isomerization decreased from 12.6 at 200 °C to 5.47 at 300 °C. The activation energies for the primary reactions were estimated and compared with those in the r

ISSN:0009-4536    

DOI:10.1002/jccs.199400019

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractWhereas reaction of [PhCH2NMe3]2|Te6Fe8(CO)24] (1) in refluxing CH2CI2forms Fe2(CO)6(μ0‐) TeCH2Te), treatment of 1 with Ph2SnCl2or Mel gave the oxidation product Te2Fe3(CO)9. Oxidation of 1 with [Cu(CH3CN)4]BF4afforded Te2Fe3(CO)9in good yield. Cluster 1 was converted to [PhCH2NMe3][Te4Fe5(CO)14] (2) in MeOH/CH2Cl2solution. Cluster 2 was structurally characterized by single‐crystal X‐ray diffraction and spectral methods. Complex 2 is composed of two Te2Fe2(CO)6fragments linked by one Fe(CO)2group. 2 crystallizes in the orthorhombic space group Pbcn with a = 13.351 (4) Å, b = 13.417 (4) Å, c = 26.077 (3) Å, V = 4671 (2)

ISSN:0009-4536    

DOI:10.1002/jccs.199400020

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe point charge in Parr's simple bond charge model is replaced by the exchange charge, which can be evaluated according to a simple ab initio method. The calculated exchange charge correlate well with the experimental values of force constants and dissociation energies for homonuclear diatomic molecules H2, Li2, F2, Na2and Cl2.

ISSN:0009-4536    

DOI:10.1002/jccs.199400021

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractBoth C10H21‐18‐crown‐5 and C10H21‐15‐crown‐5 were successfully synthesized and exhibited the distinctive characteristics of surfactants. Fluorescence of pyrene was used as a sensitive probe to study the micelle formation of the crown ether surfactant. The variation of the intensity ratio (I1/I3) of the first and third vibrational fluorescence bands of pyrene was employed to determine the critical micellar concentration (CMC). Both CMC and cloud points were found to depend on the kinds of cations and the ionic strength in solution. The quenching of pyrene fluorescence is also investigated for some cations under micelle and non‐micelle

ISSN:0009-4536    

DOI:10.1002/jccs.199400022

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractSelective ring opening of the cyclopropyl moiety of binor‐S was accomplished by several methods including acidic hydrolysis, bromination, and bydrobromination. The crystal structure of dibromide adduct3was solved by X‐ray diffraction analysis. Debrominations of3yielded either1or4a, whereas dehydrobromination yielded a 3‐substituted monobromide6a. The mechanism of conversion of3to6ais depicted as involving intermediate7; the existence of7is supported by the isolation of olefin8. Oxidation of alcohol4cproduced ketone11awhich was either oxidized to lactone12or transformed to a methylene derivative11b. Hydroboration of11bfollowed by quenching with hydrogen peroxide produced a hydroxymethyl derivat

ISSN:0009-4536    

DOI:10.1002/jccs.199400023

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

Abstractα‐Enone sugars such as 2,3‐dideoxy‐α‐D‐hex‐2‐enopyranasid‐4‐ulosesIand 3,4‐dideoxy‐α‐D‐hex‐3‐enopyranosid‐2‐ulosesIIinvolving the corresponding C‐2 and C‐4 methylated sugars5, 10aand10bwere successfully synthesized from D‐glucose in

ISSN:0009-4536    

DOI:10.1002/jccs.199400024

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractSynthesis of tertiary‐amyl methyl ether (TAME) was carried out in the temperature range 40–70 ° Cusing a sulfonic acid resin as the catalyst. Thermodynamic data were calculated from the equilibrium concentration of the components in a stirred batch reactor by the Unifac method. The enthalpy change of TAME formation was calculated to be (−20.4 ± 0.8) kJ/mol and the equilibrium constant is expressed as Ka = 3.94 × 10−4exp (20400/RT). For the kinetic tests, a homogeneous solution system was selected to interpret experimental results. The activation energy of the forward reaction was calculated to be (94.0 ± 1.5) kJ/mol and the rate constant is expressed as k2= 5.31 × 1011exp (−94000/RT). The validity of this kinetic model was verified by fitting exp

ISSN:0009-4536    

DOI:10.1002/jccs.199400025

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY