共查询到20条相似文献,搜索用时 31 毫秒
1.
The basic kinetic parameters of thermal polymerization of hexafluoropropylene, namely, general rate constants, degree of polymerization,
and their temperature and pressure dependences in the range of 230–290 °C and 2–12 kbar (200–1200 MPa) were determined. The
activation energy (E
act = 132±4 kJ mol−1) and activation volume (ΔV
0
≠ = −27±1 cm3 mol−1) were calculated. The activation energy of thermal initiation of polymerization was estimated. The reaction scheme based
on the assumption about a biradical mechanism of polymerization initiation was proposed. 相似文献
2.
A. V. Mitin 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(13):2314-2319
The He2 and Be2 ground state potential curves have been calculated by extrapolating to an infinite basis BSSE corrected MRCI total energies
obtained with large Gaussian basis sets, large reference configuration spaces, and pseudo-natural molecular orbitals. The
calculated D
e = 11.0031 K and R
e = 5.607 a.u. of He2 are in an excellent agreement with D
e = 11.006 ± 0.004 K and R
e = 5.608 ± 0.012 a.u. obtained recently by SAPT with SM energy correction. The obtained Be2 non-relativistic D
e = 822 cm−1 and relativistically corrected D
e = 818 cm−1 are in a good agreement with experimental D
e = 790 ± 30 cm−1 and the value of 829 ± 64 cm−1 obtained recently by a quantum Monte Carlo method. 相似文献
3.
Relativistic energy-consistent small-core lanthanide pseudopotentials of the Stuttgart–Bonn variety and extended valence
basis sets have been used for the investigation of the dimers La2 and Lu2. It was found that the ground states for La2 and Lu2 are most likely 1∑
g
+ (σ
g
2π
u
4) and 3∑
g
− (4f
144f
14σ
g
2σ
u
2πu
2), respectively. The molecular constants including error bars were derived from multireference configuration interaction as
well as coupled-cluster calculations, taking into account corrections for atomic spin–orbit splitting as well as possible
basis set superposition errors. The theoretical values for La2 (R
e=2.70±0.03 ?, D
e=2.31±0.13 eV, ωe=186±13 cm−1) show good agreement with the experimental binding energy (D
e=2.52±0.22 eV), but the experimental vibrational constant in an Ar matrix (ωe=236±0.8 cm−1) is significantly higher. For Lu2 the theoretical values (R
e=3.07±0.03 ?, D
e=1.40±0.12 eV, ωe=123±1 cm−1) are in overall excellent agreement with experimental data (D
e=1.43±0.34 eV, ωe=122± 1 cm−1). The electronic structures of La2 and Lu2 are compared to those other lanthanide dimers and trends in the series are discussed.
Received: 25 March 2002 / Accepted: 2 June 2002 / Published online: 21 August 2002 相似文献
4.
Terézia Vojtylová Dana Dospivová Olga Třísková Iveta Pilařová Přemysl Lubal Marta Farková Libuše Trnková Petr Táborský 《Chemical Papers》2009,63(6):731-737
Acidobasic properties of purine and pyrimidine bases (adenine, cytosine) and relevant nucleosides (adenosine, cytidine) were
studied by means of glass-electrode potentiometry and the respective dissociation constants were determined under given experimental
conditions (I = 0.1 M (NaCl), t = (25.0 ± 0.1) °C): adenine (pK
HL = 9.65 ± 0.04, pK
H2L = 4.18 ± 0.04), adenosine (pK
H2L = 3.59 ± 0.05), cytosine (pK
H2L = 4.56 ± 0.01), cytidine (pK
H2L = 4.16 ± 0.02). In addition, thermodynamic parameters for bases: adenine (ΔH
0 = (−17 ± 4) kJ mol−1, ΔS
0 = (23 ± 13) J K−1 mol−1), cytosine (ΔH
0 = (−22 ± 1) kJ mol−1, ΔS
0 = (13 ± 5) J K−1 mol−1) were calculated. Acidobasic behavior of oligonucleotides (5′CAC-CAC-CAC3′ = (CAC)3, 5′AAA-CCC-CCC3′ = A3C6, 5′CCC-AAA-CCC3′ = C3A3C3) was studied under the same experimental conditions by molecular absorption spectroscopy. pH-dependent spectral datasets
were analyzed by means of advanced chemometric techniques (EFA, MCR-ALS) and the presence of hemiprotonated species concerning
(C+-C) a non-canonical pair (i-motif) in titled oligonucleotides was proposed in order to explain experimental data obtained according to literature. 相似文献
5.
Predrag Djurdjevi? Ratomir Jeli? Ljubinka Joksovi? Mirjana Cvijovi? 《Monatshefte für Chemie / Chemical Monthly》2006,12(2):717-735
Solution equilibria between aluminium(III) ion and L-aspartic acid were studied by potentiometric, 27Al, 13C, and 1H NMR measurements. Glass electrode equilibrium potentiometric studies were performed on solutions with ligand to metal concentration
ratios 1:1, 3:1, and 5:1 with the total metal concentration ranging from 0.5 to 5.0 mmol/dm3 in 0.1 mol/dm3 LiCl ionic medium, at 298 K. The pH of the solutions was varied from ca. 2.0 to 5.0. The non-linear least squares treatment of the data performed with the aid of the Hyperquad program, indicated
the formation of the following complexes with the respective stability constants log βp,q,r given in parenthesis (p, q, r are stoichiometric indices for metal, ligand, and proton, respectively): Al(HAsp)2+ (log β1,1,1 = 11.90 ± 0.02); Al(Asp)+ (log β1,1,0 = 7.90 ± 0.03); Al(OH)Asp0 (log β1,1,−1 = 3.32 ± 0.04); Al(OH)2Asp− (log β1,1−2 = −1.74 ± 0.08), and Al2(OH) Asp3+ (log β2,1,−1 = 6.30 ± 0.04). 27Al NMR spectra of Al3+ + aspartic acid solutions (pH 3.85) indicate that sharp symmetric resonance at δ∼10 ppm can be assigned to (1, 1, 0) complex. This resonance increases
in intensity and slightly broadens upon further increasing the pH. In Al(Asp)+ complex the aspartate is bound tridentately to aluminum. The 1H and 13C NMR spectra of aluminium + aspartic acid solutions at pH 2.5 and 3.0 indicate that β-methylene group undergoes the most pronounced changes upon coordination of aluminum as well as
α-carboxylate group in 13C NMR spectrum. Thus, in Al(HAsp)2+ which is the main complex in this pH interval the aspartic acid acts as a bidentate ligand with –COO− and –NH2 donors closing a five-membered ring. 相似文献
6.
Predrag Djurdjević Ratomir Jelić Ljubinka Joksović Mirjana Cvijović 《Monatshefte für Chemie / Chemical Monthly》2006,137(6):717-735
Summary. Solution equilibria between aluminium(III) ion and L-aspartic acid were studied by potentiometric, 27Al, 13C, and 1H NMR measurements. Glass electrode equilibrium potentiometric studies were performed on solutions with ligand to metal concentration
ratios 1:1, 3:1, and 5:1 with the total metal concentration ranging from 0.5 to 5.0 mmol/dm3 in 0.1 mol/dm3 LiCl ionic medium, at 298 K. The pH of the solutions was varied from ca. 2.0 to 5.0. The non-linear least squares treatment of the data performed with the aid of the Hyperquad program, indicated
the formation of the following complexes with the respective stability constants log βp,q,r given in parenthesis (p, q, r are stoichiometric indices for metal, ligand, and proton, respectively): Al(HAsp)2+ (log β1,1,1 = 11.90 ± 0.02); Al(Asp)+ (log β1,1,0 = 7.90 ± 0.03); Al(OH)Asp0 (log β1,1,−1 = 3.32 ± 0.04); Al(OH)2Asp− (log β1,1−2 = −1.74 ± 0.08), and Al2(OH) Asp3+ (log β2,1,−1 = 6.30 ± 0.04). 27Al NMR spectra of Al3+ + aspartic acid solutions (pH 3.85) indicate that sharp symmetric resonance at δ∼10 ppm can be assigned to (1, 1, 0) complex. This resonance increases
in intensity and slightly broadens upon further increasing the pH. In Al(Asp)+ complex the aspartate is bound tridentately to aluminum. The 1H and 13C NMR spectra of aluminium + aspartic acid solutions at pH 2.5 and 3.0 indicate that β-methylene group undergoes the most pronounced changes upon coordination of aluminum as well as
α-carboxylate group in 13C NMR spectrum. Thus, in Al(HAsp)2+ which is the main complex in this pH interval the aspartic acid acts as a bidentate ligand with –COO− and –NH2 donors closing a five-membered ring. 相似文献
7.
Jonathan F. Ojo Jide Ige Grace O. Ogunlusi Olanrewaju Owoyomi Esan S. Olaseni 《Transition Metal Chemistry》2006,31(6):782-785
The kinetics of the reactions between Fe(phen)
3
2+
[phen = tris–(1,10) phenanthroline] and
Co(CN)5X3− (X = Cl, Br or I) have been investigated in aqueous acidic solutions at I = 0.1 mol dm−3 (NaCl/HCl). The reactions were carried out at a fixed acid concentration ([H+] = 0.01 mol dm−3) and the second-order rate constants for the reactions at 25 °C were within the range of (0.151–1.117) dm3 mol−1 s−1. Ion-pair constants K
ip for these reactions, taking into consideration the protonation of the cobalt complexes, were 5.19 × 104, 3.00 × 102 and 4.02 × 104 mol−1 dm−3 for X = Cl, Br and I, respectively. Activation parameters measured for these systems were as follows: ΔH* (kJ K−1 mol−1) = 94.3 ± 0.6, 97.3 ± 1.0 and 109.1 ± 0.4; ΔS* (J K−1) = 69.1 ± 1.9, 74.9 ± 3.2 and 112.3 ± 1.3; ΔG* (kJ) = 73.7 ± 0.6, 75.0 ± 1.0 and 75.7 ± 0.4; E
a
(kJ) = 96.9 ± 0.3, 99.8 ± 0.4, and 122.9 ± 0.3; A (dm3 mol−1 s−1) = (7.079 ± 0.035) × 1016, (1.413 ± 0.011) × 1017, and (9.772 ± 0.027) × 1020 for X = Cl, Br, and I respectively. An outer – sphere mechanism is proposed for all the reactions. 相似文献
8.
Novikov Vladimir P. Tarasenko Svetlana A. Samdal Svein Vilkov Lev V. 《Structural chemistry》2000,11(2-3):111-120
Gas electron diffraction data are applied to determine the geometrical parameters of the octamethylcyclotetrasilane molecule using a dynamic model in which the ring puckering is treated as a large amplitude motion. The structural parameters and parameters of the potential function were refined, taking into account the relaxation of the molecular geometry estimated from ab initio calculations at the Hartree–Fock level of theory using a 6-311G** basis set. The potential function has been described as V() = V
0[(/
e
)2 – 1]2 with V
0 = 1.0 ± 0.5 kcal/mol and
e
= 28.3 ± 1.9°, where is the puckering angle of the ring. The geometric parameters at the minimum of V() (r
a in Å, in degrees and errors given as three times the standard deviations including a scale error) are as follows: r(Si—C)av = 1.894(3), r(Si—Si) = 2.363(3), r(C—H) = 1.104(3), CSiC = 109.5(6), SiSiSi = 88.2(2), SiCH = 111.7(6), C = 4.1, where the tilt C was estimated from ab initio constraints. The structural parameters are compared with those obtained for related compounds. 相似文献
9.
Stefan Perişanu Iulia Contineanu Mircea D. Banciu Hui Zhao Nigam Rath James Chickos 《Structural chemistry》2006,17(6):639-648
Condensed and gas phase enthalpies of formation of 3:4,5:6-dibenzo-2-hydroxymethylene-cyclohepta-3,5-dienenone (1, (−199.1 ± 16.4), (−70.5 ± 20.5) kJ mol−1, respectively) and 3,4,6,7-dibenzobicyclo[3.2.1]nona-3,6-dien-2-one (2, (−79.7 ± 22.9), (20.1 ± 23.1) kJ mol−1) are reported. Sublimation enthalpies at T=298.15 K for these compounds were evaluated by combining the fusion enthalpies at T = 298.15 K (1, (12.5 ± 1.8); 2, (5.3 ± 1.7) kJ mol−1) adjusted from DSC measurements at the melting temperature (1, (T
fus, 357.7 K, 16.9 ± 1.3 kJ mol−1)); 2, (T
fus, 383.3 K, 10.9 ± 0.1) kJ mol−1) with the vaporization enthalpies at T = 298.15 K (1, (116.1 ± 12.1); 2, (94.5 ± 2.2) kJ mol−1) measured by correlation-gas chromatography. The vaporization enthalpies of benzoin ((98.5 ± 12.5) kJ mol−1) and 7-heptadecanone ((94.5 ± 1.8) kJ mol−1) at T = 298.15 K and the fusion enthalpy of phenyl salicylate (T
fus, 312.7 K, 18.4 ± 0.5) kJ mol−1) were also determined for the correlations. The crystal structure of 1 was determined by X-ray crystallography. Compound
1 exists entirely in the enol form and resembles the crystal structure found for benzoylacetone. 相似文献
10.
Geometric parameters of dimethylphenylphosphine molecule were determined by gas-phase electron diffraction using a dynamic model in which the rotation of the PMe2 group is treated as large-amplitude motion. Refinement of the structural parameters and parameters of the potential function was performed taking into account the geometry relaxation on the basis of HF/6-311++G** calculations. The internal rotation potential has a single minimum at 0° ( is the angle between the bisector of the MePMe angle and the phenyl ring plane) and may be described by the function of the form V() = 0.5V
2(1 - cos2), where V
2 = 0.38±0.36 kcal mol-
1. The data obtained are compared with those for related molecules. Steric effects affect the geometry of the phenylphosphine molecule more significantly than does p- interaction. 相似文献
11.
Density functional theory (DFT) calculations were carried out to investigate the organic field effect transistor (OFET) performance
of the symmetrical metal-free tetrakis (1,2,5-thiadiazole) porphyrazine (S4)PzH2 and tetrakis (1,4-diamyloxybenzene) (A4)PzH2 as well as the low-symmetry metal-free porphyrazine with annulated 1,2,5-thiadiazole and 1,4-diamyloxybenzene groups in the
ratio 2:2 (cis) and 1:3, that is, (cis-S2A2)PzH2 and (SA3)PzH2, (S = 1,2,5-thiadiazole ring, A = annulated 1,4-diamyloxy-benzene ring, Pz = porphyrazine) in terms of the highest occupied
molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy, ionization energy (IE), electron affinity
(EA), and their reorganization energy (λ) during the charge-transport process. On the basis of Marcus electron transfer theory, electronic couplings (V) and field effect transistor (FET) properties for the four compounds with known crystal structure have been calculated. The
electron transfer mobility (μ−) is revealed to be 0.056 cm2·V−1·s−1 for (S4)PzH2. The hole transfer mobility (μ+) is 0.075, 0.098, and 8.20 cm2·V−1·s−1 for (cis-S2A2)PzH2, (SA3)PzH2, and (A4)PzH2, respectively. The present work represents the theoretical effort towards understanding the OFET properties of symmetrical
and unsymmetrical porphyrazine derivatives with annulated 1,2,5-thiadiazole and 1,4-diamyloxybenzene.
Supported by the National Natural Science Foundation of China (Grant No. 50673051) and Beijing Municipal Commission of Edueation 相似文献
12.
We have obtained interaction dipole moment curves for the rare gas heterodiatoms Rg...Xe (Rg = He, Ne, Ar, and Kr) from conventional ab initio and density functional theory calculations with flexible Gaussian-type basis sets. All methods seem to reproduce fairly similar dipole moment curves for all pairs. Our best values for the interaction dipole moment (at the respective experimental equilibrium separation R
e) were obtained at the coupled-cluster theory with single, double, and perturbatively linked triple excitations level of theory: μint(RgXe)/eα0 = − 0.0025(He), − 0.0047(Ne), − 0.0055(Ar), and − 0.0037(Kr). The same trend (in absolute terms) is observed at the MP2 level of theory for the derivative of the dipole moment at R
e, as (dμint (RgXe)/dR)
e
/e = 0.0043 (He), 0.0082 (Ne), 0.0091 (Ar), and 0.0059 (Kr). Around R
e
, μint(HeXe) ≡ μHeXe varies at the MP2 level of theory as [μHeXe(R) − μHeXe(R
e)]/ea0 = 0.0043(R − R
e) − 0.0033(R − R
e)2 + 0.0018(R − R
e)3 − 0.0005(R − R
e)4. 相似文献
13.
14.
The bis(chelated) complex of CrV(0) derived from the dianion (L2
−) of 2-ethyl-2-hydroxybutanoic acid is readily reduced to a bis(chelate of CrIII, featuring the monoanion (LH−) [Cr
V(0)(L2−)2]−+4H++H2O+2e−→[CrIII(OH2)2(LH−
2]+ of this acid. Potentials estimated by Ghosh in 1993 for this 2e− change, E0 (pH 0) 1.32 V, Eeff (pH 3.3) 0.93 V, are in accord with the nearly irreversible reductions of the Cr(V) species (in 1∶1 ligand buffer) by Fe2+, V02+, IrCl6
3
− and I−, whereas lower values reported by Bose in 1996, E0 (pH 0) 0.84 V, Eeff (pH 3.3) 0.45 V, are potentiometrically inconsistent with these conversions. A similar discrepancy is noted for potentials
for Cr(V,IV) estimated in 1996, E0 (pH 0) 0.84 V, Eeff (pH 3.3) 0.46 V, which, wholly contrary to observation, predict that the reductions of excess Cr(V) to CR(IV) by Fe2+, V02+, and I− are thermodynamically disfavored. 相似文献
15.
Helena Dodziuk Anna Bielejewska Wojciech Schilf Haruhisa Ueda 《Central European Journal of Chemistry》2011,9(6):1056-1061
The NMR spectra of [2.2]paracyclophane with β- or γ-cyclodextrin in DMF-d7 at room temperature do not show significant complexation, while HPLC of the complexes in mixed H2O:alcohol solvents demonstrate complexation with different stoichiometries. At 243 K in DMF solution the H3 and H5 NMR signals
of γ-cyclodextrin (but not β) exhibit complexation-induced chemical shifts denoting complex formation. According to HPLC,
at room temperature the [2.2]paracyclophane complex with β-cyclodextrin in 20% H2O:EtOH exhibits 1:2 stoichiometry with K
1 = 1×102 ± 2, K
2 = 9.0×104 ± 2×103 (K = 9×106) while that with γ-cyclodextrin in 50% H2O:MeOH exhibits 1:1 stoichiometry with K
1 = 4×103 ± 150 M−1. Thermodynamic parameters for both complexes have been estimated from the retention time temperature dependence. For the
β-cyclodextrin complexation at 25°C ΔG
0
CD is −39.7 kJ mol−1 while ΔH
0
CD and ΔS
0
CD are −88.2 kJ mol−1 and −0.16 kJ mol−1 K−1. For γ-cyclodextrin, the corresponding values are ΔG
0
CD = −20.5 kJ mol−1, ΔH
0
CD = −33.5 kJ mol−1 and ΔS
0
CD = −0.04 kJ mol−1 K−1.
相似文献
16.
Electrocatalytic oxygen reduction was studied on a RuxFeySez(CO)n cluster catalyst with Vulcan carbon powder dispersed into a Nafion film coated on a glassy carbon electrode. The synthesis
of the electrocatalyst as a mixture of crystallites and amorphous nanoparticles was carried out by refluxing the transition
metal carbonyl compounds in an organic solvent. Electrocatalysis by the cluster compound is discussed, based on the results
of rotating disc electrode measurements in a 0.5 M H2SO4. A Tafel slope of −80.00±4.72 mV dec−1 and an exchange current density of 1.1±0.17×10−6 mA cm−2 was calculated from the mass transfer-corrected curve. It was found that the electrochemical reduction reaction follows the
kinetics of a multielectronic (n=4e−) charge transfer process producing water, i.e. O2+4H++4e−→2H2O.
Electronic Publication 相似文献
17.
The phase and chemical compositions of the precipitates forming in the Sr(VO3)2-VOCl2-H2O system in the V4+/V5+ = 0.11–9 range at 80–90°C are reported. At pH 1–3 and V4+/V5+ = 0.25−9, the general formula of the precipitated compounds is Sr
x
V
y
4+ V12−y
5+O31−δ·nH2)(0.37 ≤ x ≤ 1.0, 1.7 ≤ y ≤ 3.0, 0.95 ≤ δ ≤ 2.1). Polyvanadates containing the largest amount of vanadium(IV) are obtained at an initial V4+/V5+ ratio of 9 and pH 1.9. Precipitation from solutions at pH 3 takes place only in the presence of the VO2+ ion, and the highest precipitation rate is observed at V4+/V5+ = 0.11. The process is controlled by a second-order reaction on the polyvanadate surface. Under hydrothermal conditions at
180°C, Sr0.25V2O5·1.5H2O nanorods are obtained from solutions with a V4+/V5+ molar ratio of 0.1 at pH 3. The nanorods, 30–100 nm in diameter and up to 2–3 μm in length, have a layered structure with
an interlayer spacing of 10.53 ± 0.08 ?. 相似文献
18.
The stoichiometric solubility constant of eitelite (NaMg
0.5
CO
3
+2H+ ⇄ Na++0.5Mg
2+
+CO
2
(g)+H
2
O, log*K
pso
I
=14.67±0.03 was determined at I=3 m (mol kg−1) (NaClO
4
) and 25°C. The stability of magnesium (hydrogen-)carbonato complexes in this ionic medium was explicitely taken into account.
Consequently, trace activity coefficients of free ionic species, calculated from the Pitzer model with ion-interaction parameters
from the literature, were sufficient for an evaluation of the thermodynamic solubility constants and Gibbs energies of formation
for eitelite (−1039.88±0.60), magnesite (−1033.60±0.40), hydromagnesite (−1174.30±0.50), nesquehonite (−1724.67±0.40), and
brucite (−835.90±0.80 kJ-mol
−1
). The increasing solubilities of nesquehonite and eitelite at higher sodium carbonate molalities were explained by invoking
a magnesium dicarbonato complex (Mg2++2CO
3
2−
⇄ Mg(CO3)
2
2−
, log βz = 3.90 ± 0.08). A set of ion-interaction parameters was obtained from solubility and dissociation constants for carbonic
acid in 1 to 3.5 m NaClO
4
media
which reproduce these constants to 0.02 units in log K. The following Pitzer parameters are consistent with the previously
studied formation of magnesium (hydrogen-)carbonato complexes in 3m NaClO
4
. The model and Gibbs functions of solid phases derived here reproduce original solubility data (−log [H+], [Mg
2+
]
tot
) measured in perchlorate medium within experimental uncertainty.
Presented at the XXII International Conference on Solution Chemistry, July 14–19, 1991, Linz, Austria. 相似文献
19.
Mercury-mercury (II) sulphide electrode has been prepared and its electrochemical and thermodynamic behaviour has been studied
in different media. The electrode is found to show Nernstian response to pS (− log [S2−]) over the range 5.19–10.38. In the pH range 7.96–11.98, at constant [S2−]v, its response is also Nernstian. The values of thermodynamic functions, viz., ΔG0. ΔH0, and ΔS0 for the electrode reaction: Hg(3)+S2−
aμ
⇌HgS(s)+2e, have been determined. Further, the standard free energy of formation (ΔG
f
0
) and solubility product constant (K
vp
) of HgS in aqueous medium at 25±0.1°C have also been determined. 相似文献
20.
A. M. Nazarov 《High Energy Chemistry》2000,34(5):301-303
Chemiluminescence activated by the chelates Eu(tta)3phen and Eu(dbm)3phen in the thermal decomposition of diphenyldiazomethane in benzene in the presence of oxygen was examined at 333 K. The
following photophysical characteristics of the luminescence emitter, excited triplet benzophenone (BP), were found: the phosphorescence
quantum yield ϕ
BP
0
= 1.0 × 10−5, the true lifetime τ
BP
0
= 7 × 10−8 s, and the rate constant of radiative deactivationk
r, BP = ϕ
BP
0
τ
BP
0 −1
= 160 s−1. 相似文献