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1.
Molar excess enthalpies HmE, isobaric heat capacities CP,mE, volumes VmE and isothermal compressibilities κ TE for the 1,3-dioxane(3DX) + cyclohexane mixture were measured at 298.15 K, in order to compare to those of the 1,4-dioxane(4DX) + cyclohexane mixture. HmE is endothermic and the maximum value about 1.5 kJ mol −1 at x ≈ 0.45, and lower than that of the 4DX mixture by about 80 J mol −1. VmE is positive over the whole concentration and the maximum value is about 0.85 cm 3 mol −1 at x ≈ 0.45, and lower than that of the 4DX mixture. The above results suggest the energetic unstabilization, resulting in the volume expansion in the mixture. CP,mE shows the characteristic W-shaped concentration dependence, which has maximum at x ≈ 0.45 and two minima at x ≈ 0.1 and 0.9. The maximum CP,mE value for 3DX mixture shifts toward the positive side, compared to that of 4DX mixture. κ TE were estimated from speeds of sound, densities, thermal expansion coefficients and isobaric heat capacities of the pure component liquids and the mixtures. The κ TE result shows the positive concentration dependence over the whole composition range. The 3DX mixture has the similar thermodynamic properties to the 4DX mixture, despite that 4DX is the nonpolar solvent and 3DX is the dipolar liquid. this means that there exists the local dipolar interaction between 4DX molecules, and the prevalence of “microheterogeneity” in the both mixtures. 相似文献
2.
The one-electron oxidation of Mitomycin C (MMC) as well as the formation of the corresponding peroxyl radicals were investigated by both steady-state and pulse radiolysis. The steady-state MMC-radiolysis by OH-attack followed at both absorption bands showed different yields: at 218 nm G i (-MMC) = 3.0 and at 364 nm G i (-MMC) = 3.9, indicating the formation of various not yet identified products, among which ammonia was determined, G(NH 3) = 0.81. By means of pulse radiolysis it was established a total κ (OH + MMC) = (5.8 ± 0.2) × 10 9 dm 3 mol −1 s −1. The transient absorption spectrum from the one-electron oxidized MMC showed absorption maxima at 295 nm (ε = 9950 dm 3 mol −1 cm t-1), 410 nm (ε = 1450 dm 3 mol −1 cm −1) and 505 nm ( ε = 5420 dm 3 mol −1 cm −1). At 280–320 and 505 nm and above they exhibit in the first 150 μs a first order decay, κ 1 = (0.85 ± 0.1) × 10 3 s −1, and followed upto ms time range, by a second order decay, 2κ = (1.3 ± 0.3) × 10 8 dm 3 mol -1 s −1. Around 410 nm the kinetics are rather mixed and could not be resolved. The steady-state MMC-radiolysis in the presence of oxygen featured a proportionality towards the absorbed dose for both MMC-absorption bands, resulting in a Gi (-MMC) = 1.5. Among several products ammonia-yield was determined G(NH3) = 0.52. The formation of MMC-peroxyl radicals was studied by pulse radiolysis, likewise in neutral aqueous solution, but saturated with a gas mixture of 80% N2O and 20% O2. The maxima of the observed transient spectrum are slightly shifted compared to that of the one-electron oxidized MMC-species, namely: 290 nm (ε = 10100 dm3 mol−1 cm−1), 410 nm (ε = 2900 dm3 mol−1 cm−1) and 520 nm (ε = 5500 dm3 mol−1 cm−1). The O2-addition to the MMC-one-electron oxidized transients was found to be at 290 to 410 nm gk(MMC·OH + O2) = 5 × 107 dm3 mol−1 s−1, around 480 nm κ = 1.6 × 108 dm3 mol−1 s−1 and at 510 nm and above, κ = 3 × 108 dm3 mol−1 s−1. The decay kinetics of the MMC-peroxyl radicals were also found to be different at the various absorption bands, but predominantly of first order; at 290–420 nm κ1 = 1.5 × 103 s−1 and at 500 nm and above, κ = 7.0 × 103 s−1. The presented results are of interest for the radiation behaviour of MMC as well as for its application as an antitumor drug in the combined radiation-chemotherapy of patients. 相似文献
3.
The reactions of hydroxyl radical, hydrogen atom and hydrated electron intermediates of water radiolysis with N-isopropylacrylamide (NIPAAm) were studied by pulse radiolysis in dilute aqueous solutions. OH, H and e aq− react with NIPAAm with rate coefficient of (6.9±1.2)×10 9, (6.6±1)×10 9, and (1.0±0.2)×10 10 mol −1 dm 3 s −1. In OH and H radical addition to the double bond mainly -carboxyalkyl type radicals form, (OHCH 2CH √C(N- i-C 3H 7)O and CH 3CH √C(N- i-C 3H 7)O). In reaction of e aq− oxygen atom centered radical anion is produced (CH 2CHC √(N- i-C 3H 7)O −), the anion undergoes reversible protonation with p Ka=8.7. There is also an irreversible protonation on the β-carbon atom that produces the same radical as forms in H atom reaction (CH 3CH √C(N- i-C 3H 7)O). The -carboxyalkyl type radicals at low NIPAAm concentration (0.1–1 mmol dm −3) mainly disappear in self-termination reactions, 2 kt,m=8.4×10 8 mol −1 dm 3 s −1. At higher concentrations the decay curves reflect the competition of the self-termination and radical addition to monomer (propagation). The termination rate coefficient of oligomer radicals containing a few monomer units is 2 kt≈2×10 8 mol −1 dm 3 s 1. 相似文献
4.
ESR spectroscopy with modulated radical initiation is used to analyze quantitatively chemical lifetimes and CIDEP enhancements of 2-propyl-2-ol radicals, formed by photoreduction of acetone with 2-propanol in aqueous solution at T = 16°C. The bimolecular termination rate constant of the radicals is found to be diffusion controlled and to depend on the hyperfine state as a consequence of T 0---S mixing in F-pairs. CIDEP enhancements built up in geminate and in F-pairs are separated. Their relative dependence on the hyperfine state agrees with microscopic theory, which however, fails to reproduce the absolute enhancements by a factor of 4. The polarizations indicate equal reactivities towards photoreduction for the three sublevels of the 3nπ* state of acetone, and conservation of the electron spin polarization upon radical formation. The initial separation of the species in the geminate pair is found to lie within the strong exchange region, since geminate and F-pairs show equal RPM polarizations. The CIDEP enhancements limit the rate constant k22 for abstraction of the hydroxylic hydrogen of 2-propanol by 3nπ* acetone to k22 < 10 5 dm 3 mol −1 s −1. 相似文献
5.
NH 2 profiles were measured in a discharge flow reactor at ambient temperature by monitoring reactants and products with an electron impact mass spectrometer. At the low pressures used (0.7 and 1.0 mbar) the gas-phase self-reaction is dominated by a ‘bimolecular’ H 2-eliminating exit channel with a rate coefficient of k3b(300 K) = (1.3 ± 0.5) × 10 −12 cm 3 molecule −1 s −1 and leading to N 2H 2 + H 2 or NNH 2 + H 2. Although the wall loss for NH 2 radicals is relatively small ( kw ≈ 6–14 s −1), the contribution to the overall NH 2 decay is important due to the relatively slow gas-phase reaction. The heterogeneous reaction yields N 2H 4 molecules. 相似文献
6.
The effects of pressure were examined for the partitioning and rotational correlation time of nitroxide probes, TEMPO and DTBN, in dispersions of a triglyceride membrane. As external pressures increased, nitroxide probes shifted from the vesicle phase to the aqueous phase. Rotational correlation times of TEMPO and DTBN in the vesicle phase, determined from ESR line broadening, increased remarkably with increasing pressure, dependent of the molecular size of the nitroxide probes: Δ V‡ = 65.6 cm 3 mol −1 for TEMPO and 24.4 cm 3 mol −1 for DTBN. Based on the results, the microscopic properties inside the triglyceride membrane are discussed. 相似文献
7.
The self-termination rates of the benzyl radical (C 6H 5---CH 2√) and para-substituted benzyl radicals (X---C 6H 4---CH 2√) were studied in aqueous solutions. The Arrhenius parameters and activation energies were determined in the temperature range 275.5–328 K. The kinetic activation energies of these radicals were close to the dynamic activation energy of the solvent, indicating that the termination rate is controlled by diffusion. The values for the rate constants (2 kt (10 9 dm 3 mol −1 s −1)) and the activation energies ( E (kJ mol −1)) were 5.94±0.52 and 14.69±0.61 for CH 3O---C 6H 4---CH 2√, 4.52±0.2 and 17.65±1.16 for CH 37z.sbnd;C 6H 4---CH 2√, 3.07±0.45 and 17.58±0.97 for H---C 6H 4---CH 2√, 4.13±0.81 and 19.10±1.20 for Cl---C 6H 4---CH 2√ and 4.17±0.44 and 14.62±0.52 for NO 2---C 6H 4---CH 2√. 相似文献
8.
The enthalpy of formation (Δ Hf0), enthalpy of evaporation (Δ Hv0) and enthalpy of atomization (Δ Ha) of permethylcyclosilazanes (Me 2SiNH) n ( n = 3, 4) and 1,1,3,3-tetramethyldisilazane (Me 2SiH) 2NH have been determined. The enthalpies of formation of these compounds were compared with those calculated by the Benson-Buss-Franklin and Tatevskii additive schemes. In higher permethylcyclosilazanes the energy of the endocyclic Si---N bond is 306 ± 2 kJ mol −1 (73 kcal mol −1), that is 12 ± 2 kJ mol −1 (3 kcal mol −1) lower than the energy of the acyclic Si---N bond. The strain energy of the cyclotrisilazane ring is estimated to be 10.5 kJ mol −1 (2.5 kcal mol −1), whereas the energy of the ring Si---N bond is 295 kJ mol −1 (70.5 kcal mol −1). The thermochemical data for permethylcyclosilazanes were compared with the corresponding values for permethylcyclosiloxanes calculated from the results of previously reported studies. 相似文献
9.
The new strong anion exchanger (PUFIX) from polyurethane foam was prepared by coupling of the primary amine of the foam matrix with ethyl iodide. PUFIX was characterized using different tools (IR spectra, elemental analysis, density and thermal analysis). The sorption properties of the new anion exchanger (PUFIX) and chromatographic behaviour for separation and determination of palladium(II) ions at low concentrations from aqueous iodide or thiocyanate media were investigated by a batch and dynamic processes. The maximum sorption of Pd(II) was in the pH range of 0.3–2. The kinetics of sorption of the Pd(II) by the PUFIX was found to be fast with average values of half-life of sorption ( t1/2) of 3.32 min. The variation of the sorption of Pd(II) with temperature gives average values of Δ H, Δ S, Δ G and Δ E to be −38.3 kJ mol −1, −100.7 J K −1 mol −1, −8.3 and 11.8 kJ mol −1, respectively. The sorption capacity of PUFIX was 1.69 mmol g −1 for Pd(II), preconcentration factors of values ≈250 and the recovery 99–100% were achieved (R.S.D. ≈ 1.24%). The lower detection limit, 1.28 ng mL −1 was evaluated using spectrophotometric method (R.S.D. ≈ 2.46%). 相似文献
10.
UV spectra and kinetics for the reactions of alkyl and alkylperoxy radicals from methyl tert-butyl ether (MTBE) were studied in 1 atm of SF 6 by the pulse radiolysis-UV absorption technique. UV spectra for the radical mixtures were quantified from 215 to 340 nm. At 240 nm. σ R = (2.6 ± 0.4) × 10 −18 cm 2 molecule −1 and σ RO2 = (4.1 ± 0.6) × 10 −18 cm 2 molecule −1 (base e). The rate constant for the self-reaction of the alkyl radicals is (2.5 ± 1.1) × 10 −11 cm 3 molecule −1 s −1. The rate constants for reaction of the alkyl radicals with molecular oxygen and the alkylperoxy radicals with NO and NO 2 are (9.1 ± 1.5) × 10 −13, (4.3 ± 1.6) × 10 −12 and (1.2 ± 0.3) × 10 −11 cm 3 molecule −1 s −1, respectively. The rate constants given above refer to reaction at the tert-butyl side of the molecule. 相似文献
11.
The kinetic parameters were determined for C-trifluoromethylation of aniline with S-(trifluoromethyl)dibenzothiophenium triflate (1), its 3,7-dinitro derivative (2) and S-(trifluoromethyl)diphenylsulfonium triflate (3) in DMF- d7. The higher reactivity of heterocyclic 1 compared with non-heterocyclic 3 could be explained on the basis of its greatly enhanced activation entropy (ΔS ≠: −11.2 cal mol −1 K −1 for 1; −47.1 for 3), but not its enhanced activation enthalpy (ΔH ≠: 21.2 kcal mol −1 for 1; 12.1 for 3). The aromatic delocalization of the heterocyclic ring may thus be only slightly disturbed by the S-trifluoromethyl substituent. The high reactivity of 2 was attributed to the great electron deficiency caused by two nitro groups in addition to the heterocyclic salt system (ΔH ≠ 17.0 kcal mol −1, ΔS ≠ −9.1 cal mol −1 K −1 for 2). The reaction mechanism is discussed; the conventional S N2 attack mechanism was ruled out and a mechanism for a side-on attack to the CF 3-S bond may possibly be applicable. 相似文献
12.
The oxidation reaction of 2-aminophenol (OAP) to 2-aminophenoxazin-3-one (APX) initiated by 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) has been investigated in methanol at ambient temperature. The oxidation of OAP was followed by electronic spectroscopy and the rate constants were determined according to the rate law −d[OAP]/d t= kobs[OAP][TEMPO]. The rate constant, activation enthalpy and entropy at 298 K are as follows: kobs (dm 3 mol −1 s −1)=(1.49±0.02)×10 −4, Ea=18±5 kJ mol −1, Δ H‡=15±4 kJ mol −1, Δ S‡=−82±17 J mol −1 K −1. The results of oxidation of OAP show that the formation of 2-aminophenoxyl radical is the key step in the activation process of the substrate. 相似文献
13.
The state-selected reaction of CH(X 2Πν″ = 0, 1) with H 2 has been studied, in which CH was generated by IRMPD of a precursor gas, CH 3OH. The subsequent evolution of CH (ν″ = 0, 1) was monitored by the sensitive LIF technique. For the ground state and vibrationally excited state CH, the reaction with H 2 is found to depend on the total pressure in the sample cell at room temperature, which suggests that the reaction proceeds through an intermediate adduct, CH 3. The backward dissociation process is found to depend on the buffer pressure, which can be rationalized via a collision-induced backward dissociation. The decay rates of CH (ν″ = 0, 1) due to collisions with H 2 and Ar at a buffer pressure of 10 Torr are kH2 (ν″ = 1) = (2.3±0.1) × 10 −1 cm 3 molecule −1 s −1 and kAr (ν″ = 1) = (4.4±0.1) × 10 −13 cm 3 molecule −1 s −1. Possible effects of the vibrational excitation on the reaction rate of CH (ν″ = 1) are discussed. 相似文献
14.
The reactions of two triphenyl methane (TPM) dyes—crystal violet (CV +) and malachite green (MG +)—with N 3• and OH • radicals were studied by pulse radiolytic kinetic spectrophotometry. The rate constants for the reaction of the cationic dyes (D +) with N 3• are (9.0±0.6)×10 9 and (3.0±0.2)×10 9 dm 3 mol −1 s −1 respectively and those for the reaction with OH • are obtained as (8.0±0.6)×10 9 and (1.1±0.1)×10 9 dm 3 mol −1 s −1 respectively. The transient spectra resulting from the oxidation of the dyes were characterized. The time-resolved spectra indicate that the reaction with OH • radicals initially generates an adduct which subsequently dissociates to form the radical dication D •2+. The D •2+ species decay by further reaction with the parent dye. 相似文献
15.
The Arrhenius equation corresponding to the process P---Ag+P*---Ag*→---P---Ag*+P*---Ag has been determined for [(η 6- p-cymene)Ru(μ-pz) 3Ag(PPh 3)] (1) by complete line-shape analysis of the 31P NMR spectra between −40°C and +30°C. It has the form K = 10 11.8± e (−46±5 kJ mol−1/RT). The preexponential term, log A = 11.8 corresponds to a small activation entropy, whereas the activation energy, 46 kJ mol −1 is comparable to those determined for other phosphorus—metal compounds. 相似文献
16.
Pulse radiolysis technique has been employed to study the reactions of oxidizing ( √OH, N 3√) and reducing radicals (e −aq, CO 2√−, acetone ketyl radical) with 2-hydroxy-3-methoxybenzaldehyde ( o-vanillin) at different pH. Hydroxyl radicals react mostly by addition reaction forming radical adducts (λ max=420 nm) and the oxidation is only a minor process even in the alkaline region. The reaction with azide radicals produced phenoxyl radicals (λ max=340 nm), which are formed on fast deprotonation of solute radical cation. Using PMZ √+/PMZ and ABTS √−/ABTS 2− as the reference couple, different methods are employed to determine the one-electron reduction potential of o-vanillin and the average value is estimated to be 1.076±0.004 V vs. NHE at pH 6. The phenoxyl radicals of o-vanillin were able to oxidize ABTS 2− quantitatively. The e aq− is observed to react with o-vanillin with rate constant value of 2×10 10 dm 3 mol −1 s −1. CO 2√− and acetone ketyl radical are also observed to react with o-vanillin by electron transfer mechanism and showed the formation of transient absorption bands with λ max at 350 and 390 nm at pH 4.5 and 9.7, respectively. The p Ka of the one-electron reduced species was determined to be 8.1. The results indicate that the aldehydic group is the most preferred site for electron addition. 相似文献
17.
Saddle point geometries and barrier heights have been calculated for the H abstraction reaction HO 2( 2A″)+H( 2S) → H 2( 1Σ +g)+O 2( 3Σ −g) and the concerted H approach-O removing reaction HO 2 ( 2A″)+H( 2S) → H 2O( 1A 1)+O( 3P) by using SDCI wavefunctions with a valence double-zeta plus polarization basis set. The saddle points are found to be of C s symmetry and the barrier heights are respectively 5.3 and 19.8 kcal by including size consistent correction. Moreoever kinetic parameters have been evaluated within the framework of the TST theory. So activation energies and the rate constants are estimated to be respectively 2.3 kcal and 0.4×10 9 ℓ mol −1 s −1 for the first reaction, 20.0 kcal and 5.4.10 −5 ℓ mol −1 s −1 for the second. Comparison of these results with experimental determinations shows that hydrogen abstraction on HO 2 is an efficient mechanism for the formation of H 2 + O 2, while the concerted mechanism envisaged for the formation of H 2O + O is highly unlikely. 相似文献
18.
Tert-butyl chloride has been broadly studied experimentally through various techniques such as X-ray crystallography, DTA, and NMR. It was also studied experimentally through nuclear quadrupole resonance (NQR), but this study was limited and incomplete. In this paper, we present a more detailed study of TBC through the NQR of 35Cl. Our results show that near 120 K, the onset of the CH 3 groups semirotations around symmetry axis C3 takes place with an activation energy U=16.1 kJ mol −1. This intramolecular movement produces a T1 minimum near 148 K and is the dominant mechanism of the nuclear spin-lattice relaxation in phase III of this compound. In phase II of TBC, we show that there are not only methyl groups semirotations, but also semirotations of the whole molecule around a different axis from the symmetry axis C′ 3 (C–Cl bond) with an activation energy of E=10.4 kJ mol −1. 相似文献
19.
Twenty-two isomers/conformers of C 3H 6S +√ radical cations have been identified and their heats of formation (Δ Hf) at 0 and 298 K have been calculated using the Gaussian-3 (G3) method. Seven of these isomers are known and their Δ Hf data are available in the literature for comparison. The least energy isomer is found to be the thioacetone radical cation (4 +) with C2v symmetry. In contrast, the least energy C 3H 6O +√ isomer is the 1-propen-2-ol radical cation. The G3 Δ Hf298 of 4 + is calculated to be 859.4 kJ mol −1, ca. 38 kJ mol −1 higher than the literature value, ≤821 kJ mol −1. For allyl mercaptan radical cation (7 +), the G3 Δ Hf298 is calculated to be 927.8 kJ mol −1, also not in good agreement with the experimental estimate, 956 kJ mol −1. Upon examining the experimental data and carrying out further calculations, it is shown that the G3 Δ Hf298 values for 4 + and 7 + should be more reliable than the compiled values. For the five remaining cations with available experimental thermal data, the agreement between the experimental and G3 results ranges from fair to excellent. Cation CH3CHSCH2+√ (10+) has the least energy among the eleven distonic radical cations identified. Their ΔHf298 values range from 918 to 1151 kJ mol−1. Nevertheless, only one of them, CH2=SCH2CH2+√ (12+), has been observed. Its G3 ΔHf298 value is 980.9 kJ mol−1, in fair agreement with the experimental result, 990 kJ mol−1. A couple of reactions involving C3H6S+√ isomers CH2=SCH2CH2+√ (12+) and trimethylene sulfide radical cation (13+) have also been studied with the G3 method and the results are consistent with experimental findings. 相似文献
20.
The photoinduced electron transfer reactions of the triplet state of rose bengal (RB) and several electron donors were investigated by the complementary techniques of steady state and time-resolved electron paramagnetic resonance (EPR) and laser flash photolysis (LFP). The yield of radicals varied with the light fluence rate, RB concentration and, in particular, the electron donor used. Thus for L-dopa (dopa, dihydroxyphenylalanine) only 10% of RB anion radical (RB√−) was produced, with double the yield observed with NADH (NAD, nicotinamide adenine dinucleotide) as quencher and more than three times the yield observed with ascorbate as quencher. Quenching of the RB triplet was both reactive and physical with total quenching rate constants of 4 × 10 8 mol −1 dm 3 s −1 and 8.5 × 10 8 mol −1 dm 3 s −1 for ascorbate and NADH respectively. The rate constant for the photoinduced electron transfer from ascorbate to RB triplet was 1.4 × 10 8 mol −1 dm 3 s −1 as determined by Fourier transform EPR (FT EPR). FT EPR spectra were spin polarized in emission at early times indicating a radical pair mechanism for the chemically induced dynamic electron polarization. Subsequent to the initial electron transfer production of radicals, a complex series of reactions was observed, which were dominated by processes such as recombination, disproportionation and secondary (bleaching) reactions. It was observed that back electron transfer reactions could be prevented by mild oxidants such as ferric compounds and duroquinone, which were efficiently reduced by RB√−. 相似文献
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