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1.
The fluoride affinities of fluorinated alanes, AlHmF3?m (m = 1–3) were measured using energy-resolved collision-induced dissociation of fluorinated aluminate anions. The AlHmF4?m? anions were formed by reaction of dimethylethylamine-alane with fluoride ion and F2. From the measured bond dissociation energies, the fluoride affinities of fluorinated alanes are determined to be 93.2 ± 3.1, 97.5 ± 4.0, and 108.6 ± 3.7 kcal/mol for m = 3, 2, and 1, respectively. The fluoride affinities are in good agreement with the theoretical calculations at the CCSD(T)/CBS and B3LYP/6-31 + G* levels of theory. The increased Lewis acidity of more fluorinated alanes is attributed to increased positive charge density on the aluminum. 相似文献
2.
M. Agostinha R. Matos Margarida S. Miranda Victor M.F. Morais 《The Journal of chemical thermodynamics》2008,40(4):625-631
The standard (p° = 0.1 MPa) molar enthalpies of combustion and sublimation of 3,4,5-trimethoxyphenol were measured, respectively, by static bomb combustion calorimetry in oxygen atmosphere and by Calvet microcalorimetry. From these measurements, the standard molar enthalpy of formation in both the crystalline and gaseous phase, at T = 298.15 K, were derived: ?(643.4 ± 1.9) kJ · mol?1 and ?(518.1 ± 3.6) kJ · mol?1, respectively. Density functional theory calculations for this compound and respective phenoxyl radical and phenoxide anion were also performed using the B3LYP functional and extended basis sets, which allowed the theoretical estimation of the gaseous phase standard molar enthalpy of formation through the use of isodesmic reactions and the calculation of the homolytic and heterolytic O–H bond dissociation energies. There is good agreement between the calculated and experimental enthalpy of formation. Substituent effects on the homolytic and heterolytic O–H bond dissociation energies have been analysed. 相似文献
3.
Juraj Kuchár Juraj Černák Ivana Sabová Charles Kappenstein Marcela Kajňaková Martin Orendáč Roman Boča 《Solid State Sciences》2009,11(5):950-955
New bimetallic compound [CuxNi1?x(bpy)2(ox)]·4H2O (x = 0.05, ox = oxalato, bpy = 2,2′-bipyridine) was synthesized and chemically characterized. Its crystal structure is molecular. The octahedron around the metal central atom is deformed due to coordination by one bidentate oxalate anion and two bpy ligands. There are four uncoordinated water molecules in the asymmetric unit. The metal site is occupied by both Cu(II) and Ni(II) atoms in the 5:95 ratio. The complex molecules interact with water molecules through hydrogen bonds and, moreover, π–π interactions between aromatic rings lead to a 1D arrangement of molecules. The susceptibility data measured down to 2 K were analyzed using strong-coupling theory and the best agreement with the experimental data were found for g = 2.1, D/k = 5.6, E/k = 0.35, J/k = 0.2. The dehydration starts at 30 °C. As a final product of its thermal decomposition a solid solution of CuxNi1?xO was detected by X-ray powder diffraction. 相似文献
4.
《The Journal of chemical thermodynamics》2001,33(5):513-521
A calorimetric technique is described for measuring the enthalpy of dissociation liberated from solid hydrates. In this study, the enthalpies of dissociation were determined at T = 273.65 K andp = 0.1 MPa for simple and mixed hydrates of carbon dioxide, nitrogen, (carbon dioxide + nitrogen), and (carbon dioxide + nitrogen + tetrahydrofuran) using an isothermal microcalorimeter. The addition of tetrahydrofuran (THF) promoted hydrate stability and increased the number of guest molecules encaged in the small and large cavities of the hydrate lattice, resulting in lower enthalpy of dissociation, compared with structure II hydrate. The composition ratio of guest molecules did not affect the enthalpy of dissociation, which was found to be nearly constant for the same mixture. 相似文献
5.
N-acetyl-3,3-dinitroazetidine (ADNAZ) is an important precursor for synthesizing new multinitroazetidine energetic compounds. Its thermal behaviour was studied under a non-isothermal condition by DSC and TG/DTG methods, the results show that there are one melting process and one endothermic decomposition process. The specific molar heat capacity (Cp,m) of ADNAZ was determined by a continuous Cp mode of micro-calorimeter and theoretical calculation, and the Cp,m of ADNAZ was 240.37 J · K−1 · mol−1 at T = 298.15 K. The detonation velocity (D) and detonation pressure (P) of ADNAZ were estimated using the nitrogen equivalent equation according to the experimental density, the value of D and P are (6685.83 ± 3.12) m · s−1 and (18.36 ± 0.02) GPa, respectively. The free radical signals of ADNAZ were detected by electron spin resonance (ESR) technique, which is used to estimate its sensitivity. 相似文献
6.
《Journal of organometallic chemistry》2006,691(1-2):208-223
The insertion reactions of the p-complex structure (A) of silylenoid H2SiLiF into XHn molecules (X = C, Si, N, P, O, S, and F; n = 1–4) have been studied by ab initio calculations at the G3(MP2) level. The results indicate that the insertion reactions of A into X–H bonds proceed via three reaction paths, I, II, and III, forming the same products, substituted silanes H3SiXHn − 1 with dissociation of LiF, respectively, and all insertion reactions are exothermic. All the seven X–H bonds can undergo insertion reactions with A via path I and II, but only four of them, C–H, Si–H, P–H, and S–H, undergo insertion reactions via path III. The following conclusions emerge from this work: (i) the X–H insertion reactions of A occur in a concerted manner via a three-membered ring transition state; (ii) for path I and II, the stabilization energies of the A–XHn complexes decrease in the order HF > H2O > H2S > NH3 > SiH4 > CH4; (iii) for path I and II, the greater the atomic number of heteroatom (X) in a given row, the easier the insertion reaction of XHn hydrides and the larger the exothermicity, and for the second-row hydrides, the reaction barriers are lower than for the first-row hydrides; (iv) The barriers of path I are lowest in those of three pathways with the exception of A + SiH4 system, which barrier of path III is lowest. Moreover, the present study demonstrates that both electronic and steric effects play major roles in the course of insertion reactions of A into X–H bonds. 相似文献
7.
The thermal properties of {tetra-n-butylammonium bromide + tetra-n-butylammonium chloride (TBAB + TBAC)} mixed semiclathrate hydrates prepared from aqueous solutions were investigated by dissociation temperature measurements and differential scanning calorimetry (DSC). The maximum dissociation temperature of the mixed hydrate crystals at 0.1 MPa is 288.5 K for xTBAB = 0.2 {mole fraction of TBAB to (TBAB + TBAC)}, which is higher than that of the pure hydrates {T = (285.5 and 288.2) K for TBAB and TBAC hydrates, respectively}. In addition, the dissociation enthalpies of the mixed hydrates are higher than those of the pure hydrates {(5.55 ± 0.06) kJ ⋅ mol−1 H2O for pure TBAB hydrate and (5.30 ± 0.05) kJ ⋅ mol−1 H2O for pure TBAC hydrate}, with a maximum of (5.95 ± 0.12) kJ ⋅ mol−1 H2O recorded at approximately xTBAB = 0.4. It was therefore suggested that the crystal distortion in (TBAB + TBAC) mixed hydrates, caused by replacing water molecules by both bromide and chloride anions, was smaller than that observed for each pure hydrate. Consequently, the hydration numbers in the mixed hydrates were hypothesized to be slightly higher than those of the pure hydrates. 相似文献
8.
Dissociative electron attachment to SO2, NO2, NF3 and H2O2 is studied in terms of the kinetic energies of the dominant fragment ions. The O? data from SO2 show that the two major resonances at 4.6 and 7.2 eV respectively have the same dissociation limit. Similarly, the resonances at 1.8 and 3.5 eV in the O? channel in NO2 appear to have same dissociation limit of NO (X 2Π) + O?, while the resonance at 8.5 eV appears to dissociate to give NO (a 4Πi) along with O?. We find considerable internal excitation of the neutral fragments in all these cases along with that of NF3, whereas the negative ion resonance in H2O2 appears to fragment almost like a diatomic system with very little internal excitation of the OH and OH? fragments. 相似文献
9.
《Chemical physics》2005,317(1):35-42
The quantum theory of atoms in molecules (AIM) has been used to decompose dipole moment derivatives and fundamental infrared intensities of the AB3 (A = N,P; B = H,F) molecules into charge–charge flux–dipole flux (CCFDF) contributions. Calculations were carried out at the MP2(FC)/6-311++G(3d,3p) level. Infrared intensities calculated from the AIM atomic charges and atomic dipoles are within 13.8 km mol−1 of the experimental values not considering the NH3 and PH3 stretching vibrations for which the experimental bands are severely overlapped. Group V atomic dipoles are very important in determining the molecular dipole moments of NF3, PH3 and PF3 although the atomic charges account for almost all of the NH3 molecular moment. Dipole fluxes on the Group V atom are important in determining the stretching band intensities of all molecules whereas they make small contributions to the bending mode intensities. Consideration of dipole flux contributions from the terminal atoms must also be made for accurately describing the intensities of all these molecules. As expected from a simple bond moment model, charge contributions dominate for most of the NH3, NF3, and PF3 dipole moment derivatives and intensities. Charge flux and dipole flux contributions are very substantial for all the PH3 vibrations, cancelling each other for the stretching modes and reinforcing one another for the bending modes. 相似文献
10.
Protocatechuic acid, a major metabolite of antioxidant polyphenols found in green tea, has been shown to prevent carcinogenesis or antitumor growth in vitro and in vivo studies. The dilution enthalpies ΔdilHm, dissociation enthalpies ΔdisHm and thermodynamic dissociation constants Ka for protocatechuic acid in aqueous NaCl or KCl solutions were simultaneously determined by mixing-flow microcalorimetry at T = 298.15 K. In order to verify the reliability of the fitted dissociation parameters, the values of dissociation enthalpies and thermodynamic dissociation constants were also determined by isothermal titration calorimetry and electrical conductivity methods. The Ka values obtained through the proposed method agree well with those reported in literatures and obtained by other techniques. Enthalpic interaction coefficients (h2, h3 and h4) were computed according to the McMillan–Mayer model. The trends of h2 and ΔdisHm for protocatechuic acid with increasing salt molality in both the salt solutions were obtained. The different influence of KCl and NaCl on the values of h2 and ΔdisHm were discussed in terms of (solute + solute) and (solute + solvent) interactions. The results showed that it is possible to perform in a single calorimetric experiment the simultaneous determination of dilution enthalpies, dissociation enthalpies and constants in a given solvent. 相似文献
11.
《Journal of organometallic chemistry》2007,692(1-3):225-233
New tripod oligo(dibenzyl sulfide) molecules were designed by computer modeling calculations so that they would form 1:1 complexes with an Au147 nanoparticle. Twelve aromatic molecules containing two methylthiomethyl groups were used as construction units (“residues”). Combinations of the residues (“sequences”) were examined by molecular dynamic simulations, and those sequences giving the largest interaction energies with the gold nanoparticle were sought through either full search or genetic algorithm. Best-fit sequences were found for N = 5 and 6 (N is the number of “residues” in one leg of the tripod molecule). 相似文献
12.
《Journal of Molecular Structure》2006,780(1-3):151-157
The molecular structure of caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione) was determined by means of gas electron diffraction. The nozzle temperature was 185 °C. The results of MP2 and B3LYP calculations with the 6-31G7 basis set were used as supporting information. These calculations predicted that caffeine has only one conformer and some of the methyl groups perform low frequency internal rotation. The electron diffraction data were analyzed on this basis. The determined structural parameters (rg and ∠α) of caffeine are as follows: <r(NC)ring> = 1.382(3) Å; r(CC) = 1.382(←) Å; r(CC) = 1.446(18) Å; r(CN) = 1.297(11) Å; <r(NCmethyl)> = 1.459(13) Å; <r(CO)> = 1.206(5) Å; <r(CH)> = 1.085(11) Å; ∠N1C2N3 = 116.5(11)°; ∠N3C4C5 = 121. 5(13)°; ∠C4C5C6 = 122.9(10)°; ∠C4C5N7 = 104.7(14)°; ∠N9–C4=C5 = 111.6(10)°; <∠NCHmethyl> = 108.5(28)°. Angle brackets denote average values; parenthesized values are the estimated limits of error (3σ) referring to the last significant digit; left arrow in parentheses means that this parameter is bound to the preceding one. 相似文献
13.
Equilibria of EuO dissolution and dissociation in molten (NaBr + NaI) mixtures of 0.77:0.23 and 0.31:0.69 compositions at T = 973 K were studied by potentiometric titration method using Pt(O2)|ZrO2(Y2O3) indicator electrode. The solubility product indices of EuO are (7.81 ± 0.08) and (8.43 ± 0.16) in the melts of 0.77:0.23 and 0.31:0.69 compositions. The corresponding dissociation constant indices are (4.96 ± 0.04) and (5.54 ± 0.06), respectively (all the parameters are in molality). Non-dissociated EuO is the prevailing form in all the saturated solutions of europium monoxide. The decrease of the iodide ion concentration in the melts results in strengthening of EuO dissociation that is explained by introduction of harder Pearson’s base (Br−) in sodium iodide melt. In its turn this increases the fixation degree of Eu2+ in mixed halide complexes. The total solubility of EuO decreases going from NaI melt to the (bromide + iodide) mixtures that is caused by the decrease of ‘physical’ solubility of non-dissociated oxide which occupies hollow spaces of enough large size in the ionic solvents. The quantity of these hollow spaces diminishes at the sequential Br− → I− substitution. 相似文献
14.
《Vibrational Spectroscopy》2007,45(2):266-272
The solubility in the three-component system Rb2SO4–BeSO4–H2O at 25 °C was studied by the method of isothermal decrease of supersaturation. A new compound, Rb2Be(SO4)2·2H2O, is formed in a wide concentration range (from solutions containing 27.49 mass% beryllium sulfate and 20.16 mass% rubidium sulfate up to solutions containing 15.08 mass% beryllium sulfate and 39.07 mass% rubidium sulfate).Rb2Be(SO4)2·2H2O crystallizes in the monoclinic space group P21/c (a = 11.371(2) Å, b = 11.858(2) Å, c = 7.431(1) Å, β = 96.33(1), V = 996.0 Å3, Z = 4, R1 = 0.039 for 2672Fo > 4σ(Fo) and 153 variables). The crystal structure is characterized by three-membered chain fragments, composed of a central BeO2(H2O)2 polyhedron sharing corners with two SO4 tetrahedra. These bent [Be(SO4)2(H2O)2]2− units are linked by rubidium ions and hydrogen bonds to double layers and further to a three-dimensional framework structure. Rb2Be(SO4)2·2H2O is isotypic to the respective potassium sulfate and selenate compounds.The strengths of the hydrogen bonds in the title compound as deduced from the infrared wavenumbers of the uncoupled OD stretches of matrix-isolated HDO molecules (isotopically dilute sample) are discussed in terms of the Ow⋯O hydrogen bond distances, the different hydrogen bond acceptor capabilities of the sulfate oxygen atoms and the strong BeOH2 interactions (synergetic effect). The intramolecular OH bond lengths are derived from the νOD versus rOH correlation curve [H.D. Lutz, C. Jung, J. Mol. Struct. 404 (1997) 63]. 相似文献
15.
Peng Zou Jinian Shu Simon W. North 《Journal of photochemistry and photobiology. A, Chemistry》2010,209(1):56-60
The photodissociation of Cl2O has been studied at 248 and 193 nm using photofragment translational spectroscopy (PTS) experiments with tunable VUV photoionization detection. The sole products observed were Cl, O and ClO fragments. Based on the derived translational energy distributions for the ClO and Cl photofragments we conclude that at 248 nm 15% of Cl2O excitation results in three-body dissociation. At 193 nm no Cl2 fragments are observed and we conclude that the oxygen atoms arise solely from three-body dissociation. Dissociation geometries derived from forward convolution fitting suggest two qualitatively distinct three-body dissociation pathways: asymmetric concerted dissociation and symmetric concerted dissociation in agreement with recent theoretical predictions. 相似文献
16.
Manuel A.V. Ribeiro da Silva Luís M. Spencer S. Lima Ana Rita G. Moreno Ana I.M.C.L. Ferreira José R.B. Gomes 《The Journal of chemical thermodynamics》2008,40(2):155-165
The standard (p° = 0.1 MPa) molar enthalpies of formation, at T = 298.15 K, of 4-chloro-3-nitroaniline and 5-chloro-2-nitroaniline, in the condensed phase, were derived from their standard molar energies of combustion, in oxygen, to yield CO2(g), N2(g), and HCl · 600H2O(l), measured by rotating bomb combustion calorimetry. From the temperature dependence of the vapour pressures of these compounds, measured by the Knudsen effusion technique, their standard molar enthalpies of sublimation, at T = 298.15 K, were derived by means of the Clausius–Clapeyron equation. The Calvet microcalorimetry was also used to measure the standard molar enthalpies of sublimation of these compounds, at T = 298.15 K. The combination of the standard molar enthalpies of formation in the condensed phases and the standard molar enthalpies of sublimation yielded the standard molar enthalpies of formation in the gaseous phase at T = 298.15 K for each isomer. Further, the standard (p° = 0.1 MPa) molar enthalpies, entropies and Gibbs free energies of sublimation, at T = 298.15 K, were also derived.The standard molar enthalpies of formation, in the gaseous phase of all the chloronitroaniline isomers were also estimated by the Cox scheme and by the use of computational thermochemistry and compared with the available experimental values. 相似文献
17.
《Journal of Analytical and Applied Pyrolysis》2009,84(2):145-150
The thermal behavior of 4-amino-1,2,4-triazol-5-one (ATO) was studied under non-isothermal condition by DSC method in a sealed cell of stainless steel. The melting enthalpy and melting entropy of ATO are 21.34 ± 0.49 kJ mol−1 and 46.54 ± 0.30 J mol−1 K−1, respectively. The kinetic parameters were obtained from the analysis of DSC curves by Kissinger method, Ozawa method, the differential method and the integral method. The main exothermic decomposition reaction mechanism of ATO is classified as nucleation and growth, and the kinetic parameters of the reaction are Ea = 119.50 kJ mol−1 and A = 109.03 s−1. The gas products and condensed phase products of the thermal decomposition of ATO were studied on two simultaneous devices of the fast thermolysis reaction cell (gas reaction cell) in situ in conjunction with rapid scan transform infrared spectroscopy (RSFT-IR) and the solid reaction cell in situ. The heat of formation (HOF) for ATO was evaluated by G3 theory. The detonation velocity (D) and detonation pressure (P) were estimated by using the well-known Kamlet–Jacobs equation, based on the theoretical HOF and the determined crystal density. 相似文献
18.
《Polyhedron》2007,26(9-11):2230-2234
As a novel crystal engineering approach to organic molecule-based magnets, we have proposed a strategy of bio-inspired molecular assemblage based on intermolecular hydrogen bonding. Complementary hydrogen bonding between nucleobases as found in DNA is a promising non-covalent interaction for controlling the molecular arrangement of open-shell building block molecules. The hydrogen bonding of complementary nucleobases substituted with radical entities of different spin quantum numbers S, e.g., S = 1 and S = 1/2, gives rise to a heteromolecular aggregation of the S = 1 and S = 1/2 entities, leading to organic ferrimagnetics. In this study, we have designed and synthesized a thymine-substituted nitronyl nitroxide biradical (1) as a triplet (S = 1) component for the bio-inspired ferrimagnetic system. The molecular ground state of 1 has been found to be triplet (S = 1) with a singlet–triplet energy gap of 2J/kB = 21.4 K from magnetic susceptibility measurements. It has been found from X-ray structure analyses that the molecules form hydrogen-bonded aggregates in the crystalline solid state, in which the thymine moiety plays a primary role in the molecular packing. The ground-state triplet biradical serves as an S = 1 building block for bio-inspired molecule-based magnets with hydrogen-bonded nucleobase pairings. 相似文献
19.
Bis(betainium) p-toluenesulfonate monohydrate (abbreviated as BBTSH) was studied at various temperatures by X-ray diffraction, differential scanning calorimetry and vibrational spectroscopy methods. DSC curves of BBTSH show a peak at about 349 K which corresponds to water escape from the crystal, and reveal the “cold crystallization” phenomenon. BBTSH crystallizes in the P21/c space group of monoclinic system. After heating above 349 K the compound dehydrates, the crystal system changes to triclinic, the monocrystalline samples become non-merohedral twins. The BBTSH crystal comprises p-toluenesulfonic anions, monoprotonated betaine dimers and water molecules. Three kinds of hydrogen bonds are present in the crystal: strong, asymmetric and almost linear OH⋯O hydrogen bond (R(O⋯O) = 2.463(2) Å), weak OwH⋯O hydrogen bonds (R(Ow⋯O) = 2.820(2) − 2.822(2) Å) and weak CH⋯O hydrogen bonds (R(C⋯O) = 3.295(2) − 3.416(2) Å). The νaOHO vibration of the strongest hydrogen bond in the crystal gives rise to an intense broad absorption with numbers of transmission windows in the low wavenumber region of the infrared spectra. Coupling between νCO stretching vibrations of two COO groups of the betaine dimer was detected. The process corresponding to the loss of water is accompanied by the breakage of strong OH⋯O hydrogen bonds in betaine dimers and rearrangement inside half of the betaine dimers. This rearrangement results in formation of the new betaine dimers with OH∙∙∙O hydrogen bond of similar strength as corresponding bond in the hydrated form (BBTSH). 相似文献
20.
《The Journal of chemical thermodynamics》2004,36(2):115-120
Some heterogeneous reactions of oxide ion exchange (carbonate ion dissociation and magnesium oxide dissolution) in the molten {KCl + LiCl} eutectic at temperatures of (873, 973 and 1073) K were studied using an electrochemical cell with an oxygen membrane electrode Pt(O2)|ZrO2(Y2O3). The dissociation constant of the CO32− was found to increase with increasing temperature: pK (873 K)=(2.39 ± 0.05); pK (973 K)=(1.81 ± 0.09); pK (1073 K)=(1.53 ± 0.08). Removal of CO2 from the gas above the melt allows the complete transformation of CO32− to O2−. pPMgO values decrease more from (6.99 ± 0.08) to (5.41 ± 0.04). The oxobasicity indices, pI(KCl+LiCl), were calculated from the solubility data to be 3.2 at 873 K, 3.4 at 973 K, and 3.6 at 1073 K. This trend suggests an increase in acidity with increasing temperature of {KCl + LiCl}. 相似文献