摘要:

Results of recent measurements in the Ion Chemistry Laboratory at York University using the Selected-Ion Flow Tube (SIFT) technique are surveyed for reactions of singly, doubly, and triply charged buckminsterfullerene C60n+cations proceeding at room temperature in helium buffer gas at 0.35 Torr (1 Torr = 133.3 Pa). Measured rate coefficients and observed product channels for reactions with a variety of inorganic and organic molecules depend strongly on the charge state of the reactant ion. The measured rate coefficients span more than four orders of magnitude. Primary product channels observed include attachment, dissociative attachment, dissociative attachment with charge separation, single-electron transfer, dissociative single-electron transfer, and two-electron transfer. A qualitative description of the potential-energy profiles associated with these reaction channels is provided. The observed higher order chemistry of derivatized C60n+cations and of atomic exohedral adduct ions is also described. This chemistry includes cation-transfer reactions, surface derivatization, and "ball-and-chain" polymerization. Finally, results are presented that provide insight into the influence of surface strain on the reactivities of fullerene ions.Key words: fullerenes, ions, electron transfer, charge separation, surface derivatization.

ISSN:0008-4042    

DOI:10.1139/v99-158

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The complexation property and the acid dissociation kinetics of fourN,N'-dialkyl-1,10-phenanthroline-2,9-dimathanamine complexes with cobalt(II) were studied using a pH meter and a stopped-flow spectrophotometer. In 6.6 × 10-3~0.5 mol dm-3HCl (I= 0.5 mol dm-3HCl + NaCl), the dissociation rate follows the lawkobs=kK2[H+]/(1 +K2[H+]). The acid dissociation can be rationalized in terms of a four-step kinetic process involving two rapid pre-equilibrium protonations and rate-determining cleavage of the Co(II)-N(phenanthroline) bond. The temperature dependence of the rate was determined, and the appropriate thermodynamic parameters were obtained. The linear relationship between &Dgr;Hnot equaland &Dgr;Snot equalsuggests that an isokinetic temperature,Tisoof 282 ± 2 K exists.Key words:N,N'-dialkyl-1,10-phenanthroline-2,9-dimathanamine, complexation property, acid dissociation kinetics, mechanism, cobalt(II) complex

ISSN:0008-4042    

DOI:10.1139/v99-160

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The reaction between CrO2Cl2and ethylene leading to the formation of epoxide and chlorohydrin precursors or directly to 1,2-dichloroethane has been studied by density functional theory. The formation of the epoxide precursor (Cl2(O)Cr-OC2H4) was found to take place via a [3+2] addition of ethylene to two Cr=O bonds followed by rearrangement of the five-membered diol to the epoxide product. The alternative mechanisms involving a direct addition of oxygen to ethylene or the [2+2] addition of the olefin to a Cr=O bond were found to have much higher activation energies. The formation of the chlorohydrin precursor (Cl(O)Cr-OCH2=CHCl) was found to take place via a [3+2] addition to one Cr—Cl and one Cr=O bond. Pathways involving initial [2+2] addition to a Cr—Cl or Cr=O bond had much higher activation barriers. The generation of 1,2-dichloroethane is highly unfavorable with an endothermicity of 44.7 kcal/mol and an even higher activation barrier. It is suggested that the formation of epoxide and chlorohydrin from the respective precursors requires the addition of H2O.Key words: reaction mechanisms, epoxide, oxidation of ethylene, chromyl chloride, DF

ISSN:0008-4042    

DOI:10.1139/v99-148

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The 3-deoxy-D-erythro-hexos-2-ulose bis(thiosemicarbazone) (LH2) acts as a tetradentate ligand with S2N2donor sites to form a copper(II) chelate (Cu(II)L). The Cu K-edge X-ray absorption spectra analysis of a powdered sample revealed a square-planar S2N2local coordination geometry with average Cu—N and Cu—S distances of 1.92 and 2.33 Å. The EXAFS and XANES spectra and the structural parameters of a DMF solution sample indicate the retention of the square-planar local structure of the Cu(II)S2N2chromophore upon dissolution. Semiempirical PM3 calculations indicate that the structure of Cu(II)L with the copper(II) ion bound to the S2N2donor set disposed in a square-planar geometry is the most favorable one (with the highest |&Dgr;Hf|). The formation constant (logKf= 20.65 ± 0.06) of the neutral [CuL] species was calculated in 30% v/v dioxane-water and the protonation and deprotonation constants determined.Key words: bis(thiosemicarbazone), copper(II), chelate, structure, stability consta

ISSN:0008-4042    

DOI:10.1139/v99-165

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The electron self-exchange rate constant for the Cu(dmbp)22+/+couple (dmbp = 6,6'-dimethyl-2,2'-bipyridine) was measured in acetonitrile by the NMR method (kex= 5.5 × 103kg mol-1s-1, &Dgr;H* = 35.0 ± 0.3 kJ mol-1and &Dgr;S* = -56 ± 1 J mol-1K-1). Reduction reactions of Cu(bcp)22+(bcp = 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline) and Cu(dmbp)22+with Co(bipy)32+(bipy = 2,2'-bipyridine) and ferrocene (Fe(Cp)2= bis(cyclopentadienyl)iron(II)), and oxidation reactions of Cu(bcp)2+and Cu(dmbp)2+by Ni(tacn)23+(tacn = 1,4,7-triazacyclononane) and Mn(bipyO2)33+(bipyO2=N,N'-dioxo-2,2'-bipyridine) were also studied in acetonitrile. The electron self-exchange rate constants,kex, estimated for the Cu(bcp)22+/+and Cu(dmbp)22+/+couples from the oxidation reactions of Cu(bcp)2+and Cu(dmbp)2+by Ni(tacn)23+and Mn(bipyO2)33+were consistent with the directly measured values by NMR, whilekexestimated from the reduction reactions of Cu(bcp)22+and Cu(dmbp)22+by Co(bipy)32+([Cu(bcp)22+]0, [Cu(dmbp)22+]0>> [Co(bipy)32+]0) were 103times smaller than those directly measured by the NMR method. The pseudo-first-order rate constant for the reduction reaction of Cu(bcp)22+and Cu(dmbp)22+by Fe(Cp)2was not linear against the concentration of excess amounts of Fe(Cp)2. Analyses of the reactions revealed that the reductions of Cu(bcp)22+and Cu(dmbp)22+involve slow paths related to the deformation of Cu(II)N4center from tetragonal to tetrahedral coordination. The energetic preference for the deformation of Cu(II) species rather than that of Cu(I) was discussed on the basis of the ligand field activation energy (LFAE).Key words: electron transfer, copper(II) and copper(I) complexes, gated behavior

ISSN:0008-4042    

DOI:10.1139/v99-171

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The reaction of MoO2(S2CNEt2)2with Me3SiI and Me3SiNCS yielded MoOI2(S2CNEt2)2and MoO(NCS)2(S2CNEt2)2, respectively, similar to results reported for Me3SiCl and Me3SiBr. On the contrary, MoO(OSiMe3)CN(S2CNEt2)2was the only compound isolated from the reaction of MoO2(S2CNEt2)2with Me3SiCN. To study the effects of ligands on the reactivity of siloxy compounds, ab initio calculations were undertaken for Mo(OSiH3)L(S2CNH2)2molecules, for L = Cl, Br, I, NCS, and CN. The electronic density, &rgr;(r), was analysed by means of the topological theory of Atoms in Molecules (AIM). The analysis of -del2&rgr;(r) critical points (CPs) at the molybdenum valence shell showed, only in the case of L = CN, a local charge concentration region (N-type CPs) susceptible to electrophilic attacks. However, for L = Cl, Br, I, and NCS, local charge depletion sites (E-type CPs) were found in a bond-free region. The absence of any accessible E-type CPs and the presence of an N-type CP in the same region, opposite to the Mo=O group, justified the stability of Mo(OSiMe3)L(S2CNEt2)2for L = CN, and the formation of MoOL2(S2CNEt2)2for L = Cl, Br, I, and NCS by further reaction with the corresponding Me3SiL.Key words: ab initio calculation, electronic density, Mo-siloxy compound, reactivity, theoretical.

ISSN:0008-4042    

DOI:10.1139/v99-172

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Carbon-acid ionization constants,QaK(concentration quotient at ionic strength = 0.10 M), were determined by spectrophotometric titration in aqueous solution forN-methylindoline-2-one, pQaK= 15.70,N-methylindoline-2-thione, pQaK= 8.93, andN-methylindoline-2-selone, pQaK= 7.25. Rate profiles were also constructed for the thione and selone. These were interpreted, with support from the form of acid-base catalysis as well as solvent and substrate isotope effects, as representing keto - enol/enolate ion interconversion. That led to the enol acidity constant pQaE= 4.05 and the keto-enol equilibrium constant pKE= 4.88 for the thione and estimates of the limits on these quantities, pQaE< 3 and pKE> 4, for the selone.Key words: lactam, thiolactam, selenolactam, keto-enol equilibria, carbon-acid ionization constants.

ISSN:0008-4042    

DOI:10.1139/v99-169

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Experimental solubilities are reported at 25.0°C for acenaphthene dissolved in 36 different organic nonelectrolyte solvents containing ether-, carbonyl-, hydroxy-, ester, methyl-, andtert-butyl functional groups. Results of these measurements are used to test the applications and limitations of expressions derived from Mobile Order theory. For the 29 solvents for which predictions could be made computations show that Mobile Order theory does provide fairly reasonable estimates of the saturation mole fraction solubilities. Average absolute deviation between predicted and observed values is 37.8%. In comparison, the average absolute deviation is 1080% when ideal solution behavior is assumed.Key words: acenaphthene solubilities, organic nonelectrolyte solvents, solubility predictions

ISSN:0008-4042    

DOI:10.1139/v99-168

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Experiments showing that water is decomposed by the action of high-energy radiations date back to the first days of the discovery of radioactivity, a century ago. On the occasion of this anniversary, we have attempted to give a comprehensive account of the radiation chemistry of water and its solutions since its origin, with special emphasis on the various physical and chemical stages that led to the present state of this science. To this aim, we describe the effect of different intervening factors on the molecular and radical yields, including dissolved solute concentration, pH, radiation intensity (or dose rate), type and energy of the radiation, presence of oxygen, temperature, phase, and pressure. We also discuss briefly the chemical behavior of the free radicals produced in radiolyzed aqueous solutions. A good, albeit incomplete, description of the phenomena is obtained that leads to various perspectives concerning, on the one hand, the development of this science and, on the other hand, its potential for applications.Key words: radical chemistry, dilution curve, water, hydrated electron, hydroxyl and superoxide radicals, free radicals, radiolysis, chain reactions, molecular and radical yields, cell survival, linear energy transfer.

ISSN:0008-4042    

DOI:10.1139/v99-162

出版商:NRC Research Press    

年代:1999

数据来源: NRC