ISSN:0008-4042    

DOI:10.1139/cjccontents00

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The integrated values of the electron population, electron energy, nucleus–electron potential energy interaction, dipole moment and volume of the oxygen atoms, and the main properties of the O—C bond critical points, were determined by employing the theory of atoms in molecules and 6-31++G**//6-31G* wave functions for a series of 25 unbranched alkyl monoethers. These results were used to assess the degree of approximate transferability of the oxygen atom along this series in terms of the particular alkyl radicals bonded to it. It has been found that a set of six different oxygen atoms is necessary to classify all the computed values. It can be established that the oxygen atoms bonded to propyl and larger radicals can be treated, in practice, as a transferable fragment, while those bonded to at least one smaller radical are specific. Though the total HF energy and the available experimental heats of formation are well fitted by a traditional additivity scheme that distinguishes only among O, CH2, and CH3units, it has been found that the energy properties are influenced by the size of the molecule.Key words: transferability, AIM theory, ether

ISSN:0008-4042    

DOI:10.1139/v00-148

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Chlorine trioxide (Cl2O6) reacts with PdCl2to yield "ClO2Pd(ClO4)3" which is, in fact, an equimolar mixture of Pd(ClO4)2and (ClO2)2Pd(ClO4)4. The chloryl salt decomposes under vacuum to give Pd(ClO4)2. (NO2)2Pd(ClO4)4· 0.5 NO2ClO4is prepared using Pd(NO3)2·0.5 (H2O, HNO3) as the starting salt. Excess NO2ClO4sublimes easily and pure (NO2)2Pd(ClO4)4is obtained. Pd(ClO4)2and (NO2)2Pd(ClO4)4crystallize poorly; however, aP21/mspace group is proposed for the latter. A complete assignment of vibrational modes, and DFT calculations, show that Pd(ClO4)2is monomeric with chelating bidentate [ClO4] groups and Pd is in a square planar environment. In nitryl and chloryl salts, individual anions (Pd(ClO4)2-4), where unidentate [ClO4] groups interact partially with the cation or the Pd core, were characterized.Key words: palladium(II), chlorine trioxide, perchlorato complexes, chelating bidentate, vibrational spectroscopy, DFT calculations, powder X-ray diffraction.

ISSN:0008-4042    

DOI:10.1139/v00-149

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

We measured vapour pressures of aqueous acetonitrile (abbreviated as ACN) at 6, 20, and 37°C, from which excess chemical potentials of ACN (µEACN) were calculated. We also determined excess partial molar enthalpies of ACN (HEACN) at 6, 20, 30, 37, and 45°C. From these data, excess partial molar entropies of ACN (SEACN) were calculated at 6, 20, and 37°C. Using density data by Benson's group, excess partial molar volumes of ACN (VEACN) were evaluated. The response function data by the same group were also used to evaluate amplitude and wavelength of mean-square fluctuations in terms of volume, entropy, and cross between volume and entropy. All the above quantities and their dependence on the mol fraction of solute, i.e., the effect of additional solute on the above quantities were used to study the effect of acetonitrile on the molecular organization of H2O. It was found that acetonitrile works as a stronger structure-making solute than methanol. Rather its effect on H2O is about the same as that of propan-1-ol.Key words: aqueous acetonitrile, interaction functions, fluctuati

ISSN:0008-4042    

DOI:10.1139/v00-140

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Density (&rgr;), ultrasonic velocity (U), viscosity (η), and absorbance (A) of adenine in water, 1 M, 3 M, and 6 M aqueous urea solutions have been measured in the presence (and absence) of different concentrations of salts, i.e., NaCl, KCl, and CaCl2. From these measured values, the apparent molar volume (φv), experimental slope (Sv), apparent molar compressibility (φK), viscosity coefficients A and B of Jones–Dole equation, specific acoustic impedance (Z), hydration number (Sn), internal pressure (Pi), molar absorptivity (&egr;), hypochromicity (h), and oscillator strength (f) have been calculated at 298.15 K. The increasing and (or) decreasing trends of all these parameters indicate a strong interaction of urea in moderate concentration (1 M and 3 M) with adenine especially at the hydrophilic/polar and ionic sites, particularly by hydrogen bonding. However, the interaction at hydrophobic sites are relatively weaker. Higher concentrations of urea (6 M) have more denaturation effect. The &pgr;–&pgr; interactions (stacking) in adenine are more prominent in concentrated solutions and are also strengthened by the presence of cations up to an optimum concentration of salts (cut-off point). The self-association of urea and adenine is more significant in concentrated aqueous solutions and becomes negligible on dilution.Key words: interaction, adenine, urea, density, viscosity, and ultrasonic velocit

ISSN:0008-4042    

DOI:10.1139/v00-141

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Diamagnetic niobium and tantalum complexes of general formula [M(η5-C5Me5)(dithiolene)2] have been prepared (M = Nb, dithiolene = dddt2–(5,6-dihydro-1,4dithiine-2,3-dithiolate) (1); M = Ta, dithiolene = dddt2–(2); M = Nb, dithiolene = dddt2–and dmit2–(1,3-dithiole-2-thione-4,5-dithiolate) (3)). All these complexes exhibit temperature-dependent1H NMR spectra which result from a fluxional behavior of the dithiolene ligands. Their redox properties have been investigated by cyclic voltammetry and reversible oxidation processes involving the dithiolene ligands have been evidenced for the complexes1and2.Key words: niobium, tantalum, dithiolene, voltammetry cyclic, variable-temperature1H

ISSN:0008-4042    

DOI:10.1139/v00-144

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Using a second quantized formulation, an approximate diatomics in molecules (DIM) theory is presented in which all three- and four-centered electronic integrals are neglected. To ameliorate the effects of this approximation, the DIM one electron operator is constructed so that the true ab initio first-order density matrix and total energy are reproduced at the Hartree–Fock level. The resulting model was extensively tested for a variety of basis sets for its capability of capturing both the dynamic and nondynamic components of the electron correlation energy as well as the energies of excited electronic states. A modified method in which the DIM one-electron operator is formed from the initial extended Hückel guess of the Hartree–Fock orbitals was also found to produce excellent results.Key words: DIM, electron correlation energy, excited states, semiempiric

ISSN:0008-4042    

DOI:10.1139/v00-143

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

A water and methanol dew point generation device has been built up and tested. Experimental measurements of dew point for ternary methane + water + methanol were carried out between 1.01 × 105Pa to 97.84 × 105Pa and the temperature range from 248.71 to 282.93 K. A EOS-CR method (equation of state – chemical reticular) reproduces very accurately the experimental curves independently of the pressure and temperature ranges.Key words: dew point, experimental method, equation of state, excess functi

ISSN:0008-4042    

DOI:10.1139/v00-151

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Equilibrium constantsKadd= 440 andKox= 3.0 × 108for formation of a carbinolamine adduct and oxime, respectively from 9-formylfluorene and hydroxylamine, and pKa= –1.62 for protonation of the oxime, have been evaluated at 25°C in aqueous solution, based on measurements in hydroxylamine buffers, acetic acid buffers, and dilute HCl. Rate constants for hydrolysis of the oxime have been measured in the acidity range pH 4–12 M HClO4. At the highest acidities, a reaction pathway via protonated carbinolamine has been identified: evidence is presented that the reverse of this reaction involves rate-determining attack of hydroxylamine upon protonated 9-formylfluorene. By assuming that the attack of hydroxylamine is diffusion-controlled, with rate constant 3 × 109M–1s–1, a pKaforO-protonation of the aldehyde (–4.5) is derived. Taking account of the equilibrium constant for enolization of 9-formylfluorene (KE= 16.6), a pKafor forC-protonation of the enol tautomer ((–5.7) may also be obtained. Comparison of this pKawith that of the enol of acetophenone shows that the enol of 9-formylfluorene is less basic by a factor of 1010. By combining pKas for protonation of the aldehyde and oxime with measured or estimated equilibrium constants for addition of water, hydroxide ion, and hydroxylamine to 9-formylfluorene, it is also possible to obtain values of pKR= –5.3, 4.1, and 12.25 for the protonated 9-formylfluorene, protonated oxime, and 9-formylfluorene, respectively. The usefulness of pKRin providing a general measure of equilibrium constants for electrophile-nucleophile combination reactions is discussed.Key words: oxime, formyfluorene, hydrolysis, protonation, diffusio

ISSN:0008-4042    

DOI:10.1139/v00-129

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The reaction ofN,N'-bis(2,6-diisopropylphenyl)carbodiimide with lithium 2,6-diisopropylanilide, quenching with water and recrystallization from heptane produces the symmetric guanidine [DipNH]2C=NDip which crystallizes in the triclinic system, space groupP,a= 10.6513(11),b= 10.8997(11),c= 16.2961(17) Å, &agr; = 80.524(12), &bgr; = 78.921(13), &ggr; = 70.060(12)°,V= 1735.2(3) Å3,Z= 2. The molecule crystallizes with three perpendicular 2,6-diisopropylphenyl groups, which surround and shield the central CN3unit, and provide (almost) three-fold symmetry around the central atom. Its dynamic solution behaviour has been studied by VT NMR between -90 and +180°C, and is consistent with three distinct barriers to N-CArrotation. Preliminary estimates of the Gibbs free energy of activation for the lower two barriers are 56 ± 2 and 73 ± 2 kJ mol–1. Reaction of the title compound with Mo(CO)6in refluxingn-heptane produces [DipNH]2C=NDip·Mo(CO)3, a complex in which Mo(CO)3is η6-coordinated to one of the diisopropylphenyl rings.Key words: crystal structure, diisopropylaniline, guanidine, bulky lig

ISSN:0008-4042    

DOI:10.1139/v00-142

出版商:NRC Research Press    

年代:2000

数据来源: NRC