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1.
Twenty-two isomers/conformers of C3H6S+√ radical cations have been identified and their heats of formation (ΔHf) at 0 and 298 K have been calculated using the Gaussian-3 (G3) method. Seven of these isomers are known and their ΔHf 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 C3H6O+√ isomer is the 1-propen-2-ol radical cation. The G3 ΔHf298 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 ΔHf298 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 ΔHf298 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   


2.
The enthalpy of formation (ΔHf0), enthalpy of evaporation (ΔHv0) and enthalpy of atomization (ΔHa) of permethylcyclosilazanes (Me2SiNH)n (n = 3, 4) and 1,1,3,3-tetramethyldisilazane (Me2SiH)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   


3.
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 ΔH, ΔS, ΔG and ΔE 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   

4.
The coordinatively unsaturated uranium(IV) complex U[N(C6H5)2]4 has been prepared via the stoichiometric reaction of diphenylamine with [(Me3Si)2N]2 H2. U[N(C6H5)2]4 coordinates Lewis bases such as Et2O, THF, pyridine or (EtO)3PO, based on electronic absorption spectroscopy and 1H NMR studies. Exchange between U[N(C6H5)2]4 and U[N(C6H5)2]4(L), where L is THF or pyridine, is rapid on the NMR time-scale between 307 and 323 K. Measurement of equilibrium constants for L = THF provides ΔH and ΔS values of −60 kJ mol−1 and −1.8 × 102 J K−1 mol−1, respectively. U[N(C6H5)2]4 coordinates and binds (EtO)3PO much more tightly (Keq = & > 104 M−1) than THF or pyridine with the exchange rate between U[N(C6H5)2]4 and U[N(C6H5)2]4[OP(OEt)3] being close to the NMR time-scale.  相似文献   

5.
Pentacarbonyl(diethylaminocarbyne)chromium tetrafluoroborate, [(CO)5− CrCNEt2]BF4 (I), reacts with PPh3 with substitution of CO and formation of trans-tetracarbonyl(diethylaminocarbyne)triphenylphosphanechromium tetra-fluoroborate, trans-[PPh3(CO)4CrCNEt2]BF4 (III). Substitution of CO by PPh3 in neutral trans-tetracarbonyl(halo)(diethylaminocarbyne)chromium complexes, trans-X(CO)4CrCNEt2 (IVa: X = Br, IVb: X = I), leads in a reversible reaction to the corresponding tricarbonyl complexes, mer-X(PPh3)(CO)3− CrNEt2 (V), PPh3 occupying the cis-position to the carbyne ligand. With PPh3 in large excess both reactions follow a first-order rate law. This as well as the activation parameters (ΔH≠ = 104–113 kJ mol−1, ΔS≠ = 64–71 J mol−1 K−1) indicate a dissociative mechanism.  相似文献   

6.
[Re2(Ala)4(H2O)8](ClO4)6 (Re=Eu, Er; Ala=alanine) were synthesized, and the low-temperature heat capacities of the two complexes were measured with a high-precision adiabatic calorimeter over the temperature range from 80 to 370 K. For [Eu2(Ala)4(H2O)8](ClO4)6, two solid–solid phase transitions were found, one in the temperature range from 234.403 to 249.960 K, with peak temperature 243.050 K, the other in the range from 249.960 to 278.881 K, with peak temperature 270.155 K. For [Er2(Ala)4(H2O)8](ClO4)6, one solid–solid phase transition was observed in the range from 270.696 to 282.156 K, with peak temperature 278.970 K. The molar enthalpy increments, ΔHm, and entropy increments,ΔSm, of these phase transitions, were determined to be 455.6 J mol−1, 1.87 J K−1 mol−1 at 243.050 K; 2277 J mol−1, 8.43 J K−1 mol−1 at 270.155 K for [Eu2(Ala)4(H2O)8](ClO4)6; and 4442 J mol−1, 15.92 J K−1 mol−1 at 278.970 K for [Er2(Ala)4(H2O)8](ClO4)6. Thermal decompositions of the two complexes were investigated by use of the thermogravimetric (TG) analysis. A possible mechanism for the thermal decomposition is suggested.  相似文献   

7.
The molecular structure and conformational properties of O=C(N=S(O)F2)2 (carbonylbisimidosulfuryl fluoride) were determined by gas electron diffraction (GED) and quantumchemical calculations (HF/3-21G* and B3LYP/6-31G*). The analysis of the GED intensities resulted in a mixture of 76(12)% synsyn and 24(12)% synanti conformer (ΔH0=H0(synanti)−H0(synsyn)=1.11(32) kcal mol−1) which is in agreement with the interpretation of the IR spectra (68(5)% synsyn and 32(5)% synanti, ΔH0=0.87(11) kcal mol−1). syn and anti describe the orientation of the S=N bonds relative to the C=O bond. In both conformers the S=O bonds of the two N=S(O)F2 groups are trans to the C–N bonds. According to the theoretical calculations, structures with cis orientation of an S=O bond with respect to a C–N bond do not correspond to minima on the energy hyperface. The HF/3-21G* approximation predicts preference of the synanti structure (ΔE=−0.11 kcal mol−1) and the B3LYP/6-31G* method results in an energy difference (ΔE=1.85 kcal mol−1) which is slightly larger than the experimental values. The following geometric parameters for the O=C(N=S)2 skeleton were derived (ra values with 3σ uncertainties): C=O 1.193 (9) Å, C–N 1.365 (9) Å, S=N 1.466 (5) Å, O=C–N 125.1 (6)° and C–N=S 125.3 (10)°. The geometric parameters are reproduced satisfactorily by the HF/3-21G* approximation, except for the C–N=S angle which is too large by ca. 6°. The B3LYP method predicts all bonds to be too long by 0.02–0.05 Å and the C–N=S angle to be too small by ca. 4°.  相似文献   

8.
The preparations and spectroscopic characteristics are reported of a series of (trimethylgermyl)methyl- and (trimethylstannyl)methylplatinum(II) complexes with diene and P-donor ancillary ligands, cis-Pt(CH2GeMe3)2L2 (L = PPh3 or PPh2Me; L2 = dppe or cod) and cis-Pt(CH2SnMe3)2L2 (L = PPh3; L2 =cod). Thermolysis of toluene solutions of cis-Pt(CH2GeMe3)2(PPh3)2 leads to cis-Pt(Me)(CH2GeMe2CH2GeMe3)(PPh3)2 via β-alkyl migration, after (non-rate-limiting) phosphine dissociation. Estimated activation parameters (ΔH298 K = 126 ± 3 kJ mol−1, ΔS = + 17 ± 7 J mol−1 K−1 and hence Δ298 K = 121 ± 5 kJ mol−1) suggest that this system is more migration labile than its silicon analogue, primarily as a result of a lower activation enthalpy. While cis-Pt(CH2GeMe3)2(PPh2Me)2 reacts similarly but less readily, Pt(CH2GeMe3)2(dppe)2 is inert at operable temperatures. Thermolysis of Pt(CH2GeMe3)2(cod) generates 1,1,3,3,-tetramethyldi-1,3-germacyclobutane as the major organogermanium product, while from cis-Pt(CH2SnMe3)2(PPh3)2, 1,1,3,3-tetramethyldi-1,3-stannacyclobutane predominates. Mechanistic implications are discussed.  相似文献   

9.
Amberlite XAD-16 resin has been functionalized using nitrosonaphthol as a ligand and characterized employing elemental, thermogravimetric analysis and FT-IR spectroscopy. The sorption of Ni(II) and Cu(II) ions onto this functionalized resin is investigated and optimized with respect to the sorptive medium (pH), shaking speed and equilibration time between liquid and solid phases. The monitoring of the influence of diverse ions on the sorption of metal ions has revealed that phosphate, bicarbonate and citrate reduce the sorption up to 10–14%. The sorption data followed Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) isotherms. The Freundlich parameters computed are 1/n = 0.56 ± 0.03 and 0.49 ± 0.05, A = 9.54 ± 1.5 and 6.0 ± 0.5 mmol g−1 for Ni(II) and Cu(II) ions, respectively. D–R isotherm yields the values of Xm = 0.87 ± 0.07 and 0.35 ± 0.05 mmol g−1 and of E = 9.5 ± 0.23 and 12.3 ± 0.6 kJ mol−1 for Ni(II) and Cu(II) ions, respectively. Langmuir characteristic constants estimated are Q = 0.082 ± 0.005 and 0.063 ± 0.003 mmol g−1, b = (4.7 ± 0.2) × 104 and (7.31 ± 0.11) × 104 l mol−1 for Ni(II) and Cu(II) ions, respectively. The variation of sorption with temperature gives thermodynamic quantities of ΔH = −58.9 ± 0.12 and −40.38 ± 0.11 kJ mol−1, ΔS = −183 ± 10 and −130 ± 8 J mol−1 K−1 and ΔG = −4.4 ± 0.09 and −2.06 ± 0.08 kJ mol−1 at 298 K for Ni(II) and Cu(II) ions, respectively. Using kinetic equations, values of intraparticle transport and of first order rate constant have been computed for both the metal ions. The sorption procedure is utilized to preconcentrate these ions prior to their determination in tea, vegetable oil, hydrogenated oil (ghee) and palm oil by atomic absorption spectrometry using direct and standard addition methods.  相似文献   

10.
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 SN2 attack mechanism was ruled out and a mechanism for a side-on attack to the CF3-S bond may possibly be applicable.  相似文献   

11.
We have made calorimetric measurements of the enthalpy of dissolving solid ferrous chloride in water at 298 K and have derived ΔH° = −19.82 kcal mol−1 for the standard enthalpy of this process. This ΔH° is related by way of some thermodynamic calculations to other properties of iron.  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]/dt=kobs[OAP][TEMPO]. The rate constant, activation enthalpy and entropy at 298 K are as follows: kobs (dm3 mol−1 s−1)=(1.49±0.02)×10−4, Ea=18±5 kJ mol−1, ΔH=15±4 kJ mol−1, ΔS=−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.
Low-temperature heat capacities of the complex Zn(Thr)SO4·H2O (s) have been precisely measured with a small sample adiabatic calorimeter over the temperature range from 78 to 373 K. The initial dehydration temperature of the complex (Td=325.50 K) has been obtained by analysis of the heat-capacity curve. The experimental values of molar heat capacities have been fitted to a polynomial equation by least square method. The standard molar enthalpy of formation of the complex has been determined from the enthalpies of dissolution (ΔdHmΘ) of [ZnSO4·7H2O (s) +Thr (s)] and Zn(Thr)SO4·H2O (s) in 100 ml of 2 mol dm−3 HCl solvent as: ΔfHm,Zn(Thr)SO4·H2OΘ=−2111.7±3.4 kJ mol−1. These experiments were made by using an isoperibol solution calorimeter at 298.15 K.  相似文献   

14.
A quantitative attenuated total reflectance Fourier transform infrared (ATR-FT-IR) spectroscopic method is developed for the analysis of total carboxylate concentration, [COO], in aqueous solution. The short (12–13 μm) and highly reproducible pathlength of the ATR cell permits quantitative subtraction of the water peak at 1640 cm−1. Carboxylate quantitation is based on the area of the asymmetric stretching peak, which is nearly independent of compound structure. The molar absorptivity of alkyl carboxylates in water is 438 ± 58 l mol−1 cm−1, and the integrated molar absorptivity is 2.95 ± 0.08 × 104 l mol−1 cm−2 (n = 15 compounds, 0.1 M ≤ [COO] ≤ 1.5 M). The [COO] in solutions of mixed carboxylates is measured with a root mean square error of 2.4% and a small (+1.5) positive bias. The accuracy of the method is limited by the assumption that integrated absorbance is constant for all COO groups.  相似文献   

15.
The relative stabilities and electronic structures of the linkage isomers NSO and SNO have been determined by the MNDO and ab initio Hartree—Fock—Slater methods. Both approaches predict a higher stability for SNO by ca. 100 kcal mol−1, but an overlap population analysis indicates substantially higher bond orders for NSO compared to SNO. The calculations also reveal a low energy pathway with a barrier of ca. 6 kcal mol−1 for the isomerization process NSO → SNO. Good agreement was found between the observed UV-visible absorption bands for NSOmax 379 nm) and SNOmax 340 nm) and calculated values of the electronic transition energies.  相似文献   

16.
Medium-resolution spectra of the N2 b1Πu-X1Σg+ band system were recorded by 1 + 1 multiphoton ionization. In the spectra we found different linewidths for transitions to different vibrational levels in the b 1Πu state: Δν0 = 0.50 ± 0.05 cm−1, Δν1 = 0.28 ± 0.02 cm−1, Δν2 = 0.65 ± 0.06 cm−1, Δν3 = 3.2 ± 0.5 cm−1, Δν4 = 0.60 ± 0.07 cm−1, and Δν5 = 0.28 ± 0.02 cm−1. From these linewidths, predissociation lifetimes τν were obtained: τ0 = 16 ± 3 ps, τ1 > 150 ps, τ2 = 10 ± 2 ps, τ3 = 1.6 ± 0.3 ps, τ4 = 9 ± 2 ps, and τ5 > 150 ps. Band origins and rotational constants for the b 1Πuν = 0 and 1 levels were determined for the 14N2 and 14N15N molecules.  相似文献   

17.
The benzophenone-sensitised photodimerizations of N-acetyl- and N-propionyldibenz[e,f]azepine were investigated in acetone as the solvent. In both the systems, the 1H NMR analysis of the products revealed two isomeric photodimers differing in the chemical shifts and coupling constants of the cyclobutane protons, aromatic protons and the protons of the acetyl or propionyl group. Upon raising the temperature to ca. 70 °C the signals merge. The findings can be ascribed to a single thermally restricted conformational process such as the rotation about the C–N amide bond. The process exhibits free activation energies: ΔG#=(74±2) kJ mol−1 (N-acetyl) and ΔG#=(70±2) kJ mol−1 (N-propionyl).  相似文献   

18.
The rate constant for the reaction between the sulphate radical (SO4√−) and the ruthenium (II) tris-bipyridyl dication (Ru(bipy)32+) is (3.3±0.2)×109 mol−1 dm3 s−1 in 1 mol dm−3 H2SO4 and (4.9±0.5)×109 mol−1 dm3 s−1 in 0.1 mol dm−3, pH 4.7 acetate buffer. The SO4√−radical produced by the electron transfer quenching of Ru(bipy)32+* by S2O82− reacts rapidly with both acetate buffer and chloride ions. These side reactions result in a reduction in the overall quantum yield of Ru(bipy)33+ production and reduced reaction selectivity when Ru(bipy)32+* is quenched by persulphate.  相似文献   

19.
1,2-Bis(dimethylamino)-1,2-dibora-[2]ferrocenophane (1) was prepared by the reaction of 1,1′-dilithioferrocene with 1,2-dichlorobis(dimethylamino)diborane(4). In addition to hindered rotation about the B-N bond (ΔG > 80 kJ mol−1), another dynamic process was revealed by 1H and 13C NMR in solution at low temperature, and interpreted as motion of the cyclopentadienyl rings between staggered and eclipsed conformations (ΔG(233 K) = 44 ± 1 kJ mol−1).  相似文献   

20.
The new diphenolato complexes [{Mo(NO){HB(dmpz)3}Cl}2Q] where dmpz = 3,5-dimethylpyrazolyl and Q = OC6H4(C6H4O (n = 1 or 2), OC6H4CR=CRC6H4O (R = H or Et), and OC6H4CH=CHC6H4CH=CHC6H4O have been prepared and their electrochemical properties (cyclic and differential pulse voltammetry) compared with previously reported analogues where Q = OC6H4O, OC6H4EC6H4O (E = SO2, CO and S), OC6H4 (CO)C6H4 C6H4(CO)C6H4O and 1,5- and 2,7-O2C10H6. The electrochemical interaction between the redox centres in the new complexes is very weak, in contrast to that in the 1,4-benzenediolato and naphthalendiolato species. The EPR spectra of the reduced mixed-valence species [{Mo(NO){HB(dmpz)3}Cl}2Q] where Q = 1,3- and 1,4-OC6H4O and OC6H4SC6H4O shows that they are valence-trapped at room temperature, whereas those of the dianions [{Mo(NO){HB(dmpz)3}Cl}2Q]2− where Q = 1,4-OC6H4O, OC6H4EC6H4O (E = CO or S) and OC6H4CH=CHC6H4CH=CHC6H4O shows that the unpaired spins on each molybdenum centre are strongly correlated (J, the spin exchange integral AMo, the metal-hyperfine coupling constant). The electrochemical properties and the comproportionation constants for the reaction [{Mo(NO){HB(dmpz)3} Cl}2Q] + [{Mo(NO){HB(dmpz)3}Cl}O]2]2−2[{Mo(NO) {HB(dmpz)3}Cl}2Q] where Q = diphenolato bridge, are compared with related compounds containing benzenediamido and dianilido bridges.  相似文献   

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