摘要:

Measurements have been made at 288.15, 298.15, and 308.15 K with a flow microcalorimeter and densimeter to obtain heat capacities and densities forL-ascorbic acid and sodium chloride in water. These data are reported in terms of apparent molar volumesand apparent molar heat capacitiesThe volume of ionization (ΔV0) and heat capacity of ionization (ΔCP0) for the acid at 298.15 K have been calculated using a method that does not require volumetric and thermochemical data for the sodium salts of the acid. Details of our methodology are presented.

ISSN:0008-4042    

DOI:10.1139/v93-123

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Reactions of certain iridium complexes with catecholborane (HBcat) gave boron-substituent redistribution products ([Bcat2]−, B2cat3) with concomitant formation of a complex mixture of iridium hydrides. While "IrCl(PPh3)(COE)n" generated in situ from [Ir(μ-Cl)(COE)2]2(COE = cyclooctene) (2) plus 2 equivalents of PPh3also promoted HBcat degradation, this catalyst system was extremely active and selective for alkene hydroborations. Oxidative addition of HBcat to the metal centre can be the sole reaction pathway, however, with iridium complexes containing electron-rich phosphines. The unsaturated boryl complex IrHCl(Bcat)(PPri3)2was prepared and isolated in high yield from reaction of HBcat with2in the presence of four equivalents of PPri3. Ancillary carbonyl ligands also appear to facilitate oxidative addition of HBcat to an iridium centre. Addition of HBcat totrans-IrCl(CO)(PPh3)2gives the first structurally characterized metal-carbonyl boryl complextrans-IrHCl(CO)(Bcat)(PPh3)2(7). Colourless crystals of7are triclinic,(No.2) with two molecules per unit cell of dimensionsa = 12.223(2) Å,b = 12.684(2) Å,c = 14.652(1) Å, α = 70.81(1)°, β = 72.47(1)°, and γ = 71.92(1)°.

ISSN:0008-4042    

DOI:10.1139/v93-124

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

We have made calorimetric measurements of thermal effects associated with adding NaOH(aq) or HCl(aq) to aqueous solutions (pH = 1.623) of ferric chloride + sodium citrate. Combination of these measured heats with concentrations of various species calculated from stoichiometric compositions and previously knownKand ΔHvalues leads to ΔHvalues for four aqueous Fe(III)–citrate complexes. Further combination of ΔG0values from equilibrium constants with our ΔHvalues leads to ΔS0values, which are discussed in relation to conventional ideas about relationships between entropy and solute–water interactions.

ISSN:0008-4042    

DOI:10.1139/v93-125

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

X-ray crystallographic studies showed that orange crystals of the title diarylbutadiene1undergo a topochemically controlled [2 + 2] photocycloaddition when exposed to visible light to produce the cyclobutane dimer2, which is yellow. The conformation of molecule1is planar with a maximum deviation from an all-atom mean plane, including substituents, of ≤ 0.28 Å. The crystal structure of1displays pairs of molecules packed in a head-to-tail arrangement across inversion centers that allows π orbital overlap between nearest neighbor butadiene double bonds. Intermolecular distances and angles between these photoreactive atoms are, 3.517(2) Å and, 92.0(2)°; and the dihedral angle between the plane of the four photoreactive atoms and the plane of the butadiene in one molecule is 72.9°. Molecule2lies on a crystallographic inversion centre, which constrains the cyclobutane ring to absolute planarity with C—C distances of 1.558(2) and 1.569(2) Å and C—C—C angle of 90.61(1)°. The dihedral angles between the cyclobutane ring and the two phenyl rings are 81.2° for thep-nitrophenyl and 54.0° for theo-methoxyphenyl. From the crystal structures of1and2, the displacement of each of the four photoreactive atoms during the solid-state dimerization can be estimated to be ca. 1.00 Å. Crystals of1are orthorhombic,Pbca,a = 7.471(1),b = 14.283(1),c = 25.940(1) Å,Z = 8, and those of2are monoclinic,P21/c,a = 11.5396(5),b = 16.129(1),c = 7.9035(3) Å, β = 90.264(3)°,Z = 4. Both structures were solved by direct methods and refined to final values ofR = 0.0481 and 0.0512 using 2788 and 2333 observed (I > 3 σ(I)) reflections, for1and2, respectively.

ISSN:0008-4042    

DOI:10.1139/v93-126

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The X-ray crystal structure of the title material has been determined at −130 °C. Low-temperature1H1H COSY,13C1H HETCOR, and DEPT13C NMR spectra have been recorded, which permit unambiguous assignments of all carbon resonances when ring inversion is slow on the NMR timescale. The limiting low-temperature solution phase13C spectrum has many common features with the solid phase13C CPMAS spectrum recorded at 300 K. Spectra for the 7,10-tetra-deuterio derivative have also been obtained and substituent influences on13C shieldings are discussed in detail.

ISSN:0008-4042    

DOI:10.1139/v93-127

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Precise1H nuclear magnetic resonance spectral parameters are reported for salicyladehyde and its 3-fluoro and 5-fluoro derivatives in nonpolar solutions. Such data are also given for the 2-mercapto, 2-methylthio, and 2-methoxy derivatives of benzaldehyde. Comparison of the long-range coupling constants in the various compounds and their conformers shows a large perturbation of their magnitudes by hydrogen bond formation. For the salicylaldehyde system, the perturbation is particularly large for couplings involving the aldehyde proton and protons or fluorine nuclei placedorthoto the hydroxyl group. For example,5Jt(F, CHO) is reduced by about 50%. The perturbation, as expected, is much smaller for coupling constants of nuclei remote from the site of the hydrogen bond. In 2-mercaptobenzaldehyde the long-range coupling constants are also sensitive to hydrogen bond formation, those involving the sulfhydryl proton markedly so compared to the hydroxyl proton in salicylaldehyde. The strength of thebond is discussed. It is argued that the reference conformer for the mercapto compound in such a discussion is less easily defined than for salicylaldehyde becauseare similar toenergies. The experimental data for the CCl4solutions imply a free energy of formation of thebond of 4.8(5) kJ/mol at 300 K. Molecular orbital computations on the four planar conformers of each salicylaldehyde and 2-mercaptobenzaldehyde with the 6-31 G**(5D) basis are reported. For salicylaldehyde, thearrangement is taken as the reference conformer, with a computed energy of 25.7 kJ/mol relative to the hydrogen-bonded structure. For 2-mercaptobenzaldehyde, theandconformers are calculated to be isoenergetic, at 5.1 kJ/mol relative to the hydrogen-bonded conformer. Hence either arrangement serves as a reference structure in computations of the strength of the hydrogen bond. The computations are consistent with the experimental results for solutions of the molecules under discussion. An appendix gives the computed geometries of the eight planar conformers, as well as some atomic charges, allowing a rationalization of the relative energies of the conformers.

ISSN:0008-4042    

DOI:10.1139/v93-128

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

An appropriate pattern recognition method has been designed to visually discriminate between crude oils belonging to different geographic origins. Each oil is represented by a circular profile that consists of parameter axes that radiate from the centre like spokes on a wheel. One objective of this approach is to provide an optimum set of axes that will best differentiate one circular profile from another. Several parameters were considered for evaluating the oils: photo-acoustic spectroscopy (PAS), carbon-13 nuclear magnetic resonance (13C NMR, for %CA = aromatic carbon content), high-performance liquid chromatography (HPLC, for unsaturated, aromatic, and polar compounds), initial boiling point (IBP), American Petroleum Institute (API) gravity, and ultraviolet–visible spectrophotometry (for λmax = maximum absorption wavelength and ϵmax = maximum molar absorptivity). By computerized statistical evaluation, the selected parameters are PAS and HPLC for unsaturated, aromatic, and polar compounds.

ISSN:0008-4042    

DOI:10.1139/v93-129

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The kinetics of oxidation of bis(1,4,7-triazacyclononane)nickel(II), [Ni(tacn)2]2+, by the peroxodisulphate anion has been studied in water as a function of S2O82−concentration and temperature. The reaction is first order in both the nickel(II) complex and S2O82−, with a second-order rate constant of 1.13 mol dm−3s−1at 298 K. The activation energy for the reaction is 38.3 ± 1.8 kJ mol−1. The reaction was also studied at 298 K in a series of mixed aqueous solvents. Rate retardation relative to water was observed in all solvent mixtures studied. Correlation of the solvent effects on the kinetics of reaction has been made with the free energy of transfer of the initial state and the transition state.

ISSN:0008-4042    

DOI:10.1139/v93-130

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The efficacy of a new annulation method, developed for the construction of functionalized bicyclic compounds, is illustrated by conversion of the β-keto esters18and19into the bicyclo[4.3.0]non-1-enes33and34, respectively, and by transformation of 2-methoxycarbonylcyclopentanone (20) into the bicyclo[4.3.0]non-6-ene38and the bicyclo[5.3.0]dec-7-enes48and51. Application of the method to total syntheses of the structurally unusual sesquiterpenoids (±)-chiloscyphone (16) and (±)-6-epi-chiloscyphone (17) is described.

ISSN:0008-4042    

DOI:10.1139/v93-131

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

EthylE-5-(4-ethyl-2-hydroxyphenyl)-2-pentenoate (7), prepared in four steps fromm-ethylphenol (9), was converted via Wessely oxidation with lead tetraacetate followed by intramolecular Diels–Alder reaction in boiling xylene to ethyl 1-acetyloxy-6-ethyl-2,3,3a,4,5,7a-hexahydro-8-oxo-1,5-methano-1H-indene-anti-4-carboxylate (16). Hydrogenation of16followed by mild hydrolysis gave ethyl 6-ethyloctahydro-1-hydroxy-8-oxo-1,5-methano-1H-indene-anti-4-car-boxylate (24), which on oxidation with periodate gave 4-(ethoxycarbonyl)-6-ethyloctahydro-1-oxo-1H-indene-5-car-boxylic acid (26). Oxidative decarboxylation of this gave a mixture of ethyl 6-ethyl-2,3,3a,6,7,7a-hexahydro-1-oxo-1H-indene-4-carboxylate (31) and ethyl 6-ethyl-2,3,3a,4,7,7a-hexahydro-1-oxo-1H-indene-4-carboxylate (32); the latter was converted to the former by ethanolic sodium ethoxide. Hydrolysis of31with hot hydrochloric acid gave (±)-coronafacic acid (4).

ISSN:0008-4042    

DOI:10.1139/v93-132

出版商:NRC Research Press    

年代:1993

数据来源: NRC