共查询到20条相似文献,搜索用时 328 毫秒
1.
M. Agostinha R. Matos Margarida S. Miranda Natália A. B. Pinto Victor M. F. Morais N. Dhananjaya Joel F. Liebman 《Molecular physics》2013,111(14):1885-1894
The standard (p°?=?0.1?MPa) molar enthalpy of formation for solid and gaseous diphenic anhydride (2,2′-biphenyldicarboxylic anhydride, dibenz[c,e]oxepin-5,7-dione) was derived from the standard molar enthalpy of combustion, in oxygen, at T?=?298.15?K, measured by static bomb combustion calorimetry, and the standard molar enthalpy of sublimation, at T?=?298.15?K, measured by Calvet microcalorimetry: ?(258.4?±?4.9) kJ?mol?1. In addition, ab initio and density functional theory calculations have been performed at a variety of levels. The degree of aromaticity of diphenic anhydride is discussed in the context of other oxygen-containing (ring and keto) heterocycles and related carbocycles: this species is surprisingly destabilized. 相似文献
2.
Low-temperature heat capacities and standard molar enthalpy of formation of pyridine-2,6-dicarboxylic acid 下载免费PDF全文
This paper reports that the low-temperature heat
capacities of pyridine-2,6-dicarboxylic acid were measured by a
precision automatic calorimeter over a temperature range from 78~K
to 380~K. A polynomial equation of heat capacities as a function of
temperature was fitted by the least-squares method. Based on the
fitted polynomial, the smoothed heat capacities and thermodynamic
functions of the compound relative to the standard reference
temperature 298.15~K were calculated and tabulated at intervals
of 5~K. The constant-volume energy of combustion of the compound was
determined by means of a precision rotating-bomb combustion
calorimeter. The standard molar enthalpy of combustion of the
compound was derived from the constant-volume energy of combustion.
The standard molar enthalpy of formation of the compound was
calculated from a combination of the datum of the standard molar
enthalpy of combustion of the compound with other auxiliary
thermodynamic quantities through a Hess thermochemical cycle. 相似文献
3.
Sergio L. Laurella Claudia Latorre Roque Dietrich Jorge J. P. Furlong Patricia E. Allegretti 《Journal of Physical Organic Chemistry》2012,25(12):1365-1373
Mass spectrometric evidence of tautomerism is reported for β‐ketoamides. The most abundant tautomers are ketoamido and Z‐enolamido (both forming internal hydrogen bonds). The influence of temperature on the enol/keto abundance ratios is studied in order to estimate the enthalpy difference for tautomeric equilibria. Theoretical calculations have been done in order to support experimental determinations. There are consistent trends between theoretical and experimental data: Enolization is favored by electron‐withdrawing substiuents, bulky groups in α position and temperature increase. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
4.
T. S. Kon’kova Yu. N. Matyushin E. A. Miroshnichenko A. B. Vorob’ev 《Russian Journal of Physical Chemistry B, Focus on Physics》2011,5(2):298-303
A combined use of precise combustion calorimetry and reaction calorimetry made it possible to obtain the standard enthalpy
of formation of complex salts of transition metals (nickel, zinc, and cadmium) with 2-(1H-1,2,3,4-tetrazol-1-yl)acetohydrazide
ligands. The enthalpy of combustion of the ligand was determined using combustion calorimetry, based on which its standard
enthalpy of formation was calculated. For measurements by reaction calorimetry, a thermochemical cycle was designed to determine
the standard enthalpy of formation of complex salts. The enthalpies of solution in water and in a 0.1 N hydrochloric acid
solution of the ligand and complex transition metal salts were measured. Based on these data, the enthalpy of formation of
the salts and the enthalpy of formation of three new complex ions were calculated. 相似文献
5.
Low-temperature heat capacities and standard molar enthalpy of formation of N-methylnorephedrine C11H17NO(s) 下载免费PDF全文
This paper reports that low-temperature heat capacities of N-methylnorephedrine C11H17NO(s) have been measured by a precision automated adiabatic calorimeter over the temperature range from T=78K to T=400K. A solid to liquid phase transition of the compound was found in the heat capacity curve in the temperature range of T=342-364 K. The peak temperature, molar enthalpy and entropy of fusion of the substance were determined. The experimental values of the molar heat capacities in the temperature regions of T=78-342 K and T=364-400 K were fitted to two poly- nomial equations of heat capacities with the reduced temperatures by least squares method. The smoothed molar heat capacities and thermodynamic functions of N-methylnorephedrine C11H17NO(s) relative to the standard refer- ence temperature 298.15 K were calculated based on the fitted polynomials and tabulated with an interval of 5 K. The constant-volume energy of combustion of the compound at T=298.15 K was measured by means of an isoperibol precision oxygen-bomb combustion calorimeter. The standard molar enthalpy of combustion of the sample was calculated. The standard molar enthalpy of formation of the compound was determined from the combustion enthalpy and other auxiliary thermodynamic data through a Hess thermochemical cycle. 相似文献
6.
Low-temperature heat capacities and standard molar enthalpy of formation of 4-(2-aminoethyl)-phenol (C8H11NO) 下载免费PDF全文
This paper reports that low-temperature heat capacities of 4-(2-aminoethyl)-phenol (C8H11NO) are measured by a precision automated adiabatic calorimeter over the temperature range from 78 to 400 K. A polynomial equation of heat capacities as a function of the temperature was fitted by the least square method. Based on the fitted polynomial, the smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15K were calculated and tabulated at the interval of 5K. The energy equivalent, εcalor, of the oxygen-bomb combustion calorimeter has been determined from 0.68g of NIST 39i benzoic acid to be εcalor=(14674.69±17.49)J·K^-1. The constant-volume energy of combustion of the compound at T=298.15 K was measured by a precision oxygen-bomb combustion calorimeter to be ΔcU=-(32374.25±12.93)J·g^-1. The standard molar enthalpy of combustion for the compound was calculated to be ΔcHm = -(4445.47 ± 1.77) kJ·mol^-1 according to the definition of enthalpy of combustion and other thermodynamic principles. Finally, the standard molar enthalpy of formation of the compound was derived to be ΔfHm(C8H11NO, s)=-(274.68 ±2.06) kJ·mol^-1, in accordance with Hess law. 相似文献
7.
H. Othmani R. Ben Said N. Terzi N.-E. Jaidane M. Mogren Al Mogren A. Elmarghany 《Molecular physics》2019,117(13):1589-1603
ABSTRACTIn many cases, 5-fluorouracil (5-FU) is the first-line drug used in combined chemotherapy and radiotherapy treatments due to its radio-sensitization properties. It could participate in a tautomerization process similar to that of uracil, where 5-FU may couple to adenine in DNA. At present, we performed structural and spectroscopic studies using quantum chemical methods of neutral and cationic isolated 5-FU anticarcinogenic drug tautomers, either interacting with a water molecule or embedded into an implicit water solvent. Also, we determined the stationary points (both stable structures and transition states) on their ground potential energy surfaces playing a role during the tautomerization processes. For neutral and ionic species in the gas phase and in solvent, the ordering of the tautomers is found to be the same, where the di-keto form of 5-FU is the most stable structure, followed by the keto–enol and di-enol structural forms. The energy barriers for tautomerization are strongly reduced in solvent (< 0.5?eV) compared to isolated species (~2?eV). The patterns of their lowest electronic states are also computed. Our data may help for the identification of these species in vivo and in the laboratory. 相似文献
8.
T. S. Kon’kova Yu. N. Matyushin E. A. Miroshnichenko A. B. Vorob’ev 《Russian Journal of Physical Chemistry B, Focus on Physics》2009,3(6):987-989
A method for determining the enthalpies of formation of coordination compounds of Cu(II), Co(II), Zn, and Cd perchlorates
was developed. The enthalpies of solution of complex salts in water were measured. The enthalpy of combustion of the 1,5-diaminotetrazole
ligand was determined, and the enthalpy of its formation in the standard state calculated. The experimental data were used
to calculate the enthalpies of formation of the coordination compounds studied in the standard state. 相似文献
9.
任宏江 《原子与分子物理学报》2017,34(4):745-750
采用量子化学密度泛函理论B3LYP方法在6-311++G(d,p)基组水平上,对6-硫代鸟嘌呤硫醇式与硫酮式两类共14种磺化异构体的热力学稳定性进行了计算研究,全自由度优化了各物种构型,进行了振动分析,获得了各磺化异构体的零点能、焓、热力学能以及吉布斯自由能等热力学数据.分析了各异构体磺化前后稳定性的变化情况,探讨了磺化异构体的稳定性问题.结果表明,不论是硫酮式还是硫醇式磺化异构体,当H原子连接到N7上时磺化异构体稳定性均比连接到N9上时较高一些.在6-硫代鸟嘌呤磺化异构体中,STG(3,7,10,10)是最稳定的异构体,STG(1,7,10,10)、STG(1,9,10,10)和STG(1,3,7,10)等异构体也可共存,其他异构体存在的可能性均较小. 相似文献
10.
The pyruvic acid molecule and its various isomers have been studied in aqueous solution in order to understand the mechanism of decarboxylation. The tautomeric equilibrium remains in favor of the keto form in aqueous solution, but the energy difference between the two tautomers decreases. The anion also exists in the keto form in aqueous solution. Good agreement between the calculated and observed gas phase protonation and basicity values is obtained, and the calculated pKa value is also in reasonable agreement with the literature value. The importance of the catalytic mechanism may be gauged from the fact that, in the absence of an enzymatic pathway, the reaction has high activation barrier and may not occur at all. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
11.
José R. B. Gomes Luísa M. P. F. Amaral Manuel A. V. Ribeiro da Silva 《Journal of Physical Organic Chemistry》2008,21(5):365-371
The standard (p0 = 0.1 MPa) molar enthalpy of formation of 3,4‐dimethylbenzophenone was derived from the standard molar energy of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The Calvet high temperature vacuum sublimation technique was used to measure the enthalpy of sublimation of the compound. From these experimental parameters, the standard molar enthalpy of formation of 3,4‐dimethylbenzophenone, in the gaseous phase and at T = 298.15 K, was derived as ?(17.1 ± 2.9) kJ mol?1. Density functional theory was used to investigate the gas‐phase molecular energetics of the 12 dimethylbenzophenones. Molecular geometries and vibrational frequencies were computed at the B3LYP/6‐31G(d) level of theory. The larger 6‐311+G(2d,2p) basis set was used to compute the energy of all dimethylbenzophenones and of the other compounds that were considered for the estimation of the standard molar enthalpies of formation at T = 298.15 K. The calculations show that the 2,2′‐ and 4,4′‐dimethylbenzophenones are the least and most stable isomers, respectively. Finally, the calculated enthalpy of formation of the benzophenone that was also studied experimentally, 3,4‐dimethylbenzophenone, is ?16.7 kJ mol?1, which is in excellent agreement with the experimental result. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
12.
Thomas Rudin Karsten Wegner Sotiris E. Pratsinis 《Journal of nanoparticle research》2011,13(7):2715-2725
A new flame-assisted spray pyrolysis (FASP) reactor design is presented, which allows the use of inexpensive precursors and
solvents (e.g., ethanol) for synthesis of nanoparticles (10–20 nm) with uniform characteristics. In this reactor design, a
gas-assisted atomizer generates the precursor solution spray that is mixed and combusted with externally fed inexpensive fuel
gases (acetylene or methane) at a defined height above the atomizing nozzle. The gaseous fuel feed can be varied to control
the combustion enthalpy content of the flame and onset of particle formation. This way, the enthalpy density of the flame
is decoupled from the precursor solution composition. Low enthalpy content precursor solutions are prone to synthesis of non-uniform
particles (e.g., bimodal particle size distribution) by standard flame spray pyrolysis (FSP) processes. For example, metal
nitrates in ethanol typically produce nanosized particles by gas-to-particle conversion along with larger particles by droplet-to-particle
conversion. The present FASP design facilitates the use of such low enthalpy precursor solutions for synthesis of homogeneous
nanopowders by increasing the combustion enthalpy density of the flame with low-cost, gaseous fuels. The effect of flame enthalpy
density on product properties in the FASP configuration is explored by the example of Bi2O3 nanoparticles produced from bismuth nitrate in ethanol. Product powders were characterized by nitrogen adsorption, X-ray
diffraction, X-ray disk centrifuge, and transmission electron microscopy. Homogeneous Bi2O3 nanopowders were produced both by increasing the gaseous fuel content and, most notably, by cutting the air entrainment prior
to ignition of the spray. 相似文献
13.
本文通过观测7HQ在固态基质中的吸收光谱,研究7HQ被紫外光照射后物种的变化,表明光照前分子主要以烯醇构型存在。受紫外光337.1nm,照射后部分烯醇构型转变为酮式构型和其它构型,样品被光照后存放2个月,其吸收光谱仍保持不变,这些结果说明7HQ在光存储方面有潜在的应用前景。 相似文献
14.
《光谱学快报》2013,46(6):607-618
Abstract The enolisation tendencies of 1‐(o‐substituted phenyl)barbituric and ‐2‐thiobarbituric acid derivatives have been studied by observing the behaviour of the compounds in different solvents by 1H and 13C NMR. It has been found that the enolisation tendencies of the thiobarbituric acid derivatives observed in polar solvents are greater than those of the barbituric acid derivatives. The ratio of keto–enol tautomers of thiobarbituric acid derivatives in DMSO and in DMF has been calculated. 相似文献
15.
Y. Syetov 《Journal of fluorescence》2013,23(4):689-696
Energies and oscillator strengths of vertical transitions for various rotameric and tautomeric species of 2-(2′-hydroxyphenyl)benzoxazole (HBO), 2,5-bis(2-benzoxazolyl)phenol (DBP) and 2,5-bis(2-benzoxazolyl)hydroquinone (BBHQ) have been calculated in the ground and first excited states with the use of TDDFT methods. The TDDFT results demonstrate good correspondence to the frequencies of absorption and fluorescence bands of the benzoxazoles reported for measurements in supersonic jets and solution, but fail to predict relative energies of the enol and keto tautomers of DBP and BBHQ in the excited state. Low intensity of the fluorescence bands attributed to the conformations of HBO and DBP that do not undergo excited state proton transfer is shown to be caused by low concentrations of the conformations in the ground state. For the three compounds large-amplitude twisting of the keto tautomer is found to be one of radiationless processes resulting in decrease of the fluorescence with a large Stokes shift. 相似文献
16.
Marzyeh Mohammadi 《Molecular physics》2013,111(22):3356-3374
The current work is a theoretical study of the tautomerism of thymine in the gas phase. Eighteen structures were found in the isomerisation reaction of thymine, some of which are reported for the first time. Thirty hydrogen transfer reactions were carried out. In 24 of the reactions, the hydrogen abstractions N―H→O, N―H→C and C―H→O were considered. The potential energy surface for all trajectories was determined for 18 tautomers and 40 transition states. The RRKM-TST model was used to calculate the rate constants of the reactions to examine their kinetics. Nonlinear least-squares fitting was used to calculate the rate constants expressions. The interaction of sodium ion and tautomers in the gas phase was also investigated. Three types of interaction of metal cations with thymine were found. In the first, metal cations interact with a lone pair of nitrogen or oxygen tautomers. The second type is the interaction of metal cations with two nitrogen and oxygen of tautomers. The last type is the interaction of metal cations and the electron density of the π-system of thymine in which the metal ion is perpendicular to the ring of tautomers. The stability ranking of the thymine tautomers and their complexes was also determined. 相似文献
17.
I. GALETICH S. G. STAPANIAN V. SHELKOVSKY M. KOSEVICH L. ADAMOWICZ 《Molecular physics》2013,111(23):3649-3659
The temperature dependent field ionization mass spectrometry method combined with ab initio calculations was used to determine the interaction energies and the structures of 9-methylguanine-acrylamide dimers. Acrylamide mimics the side chain amide group of the natural amino acids asparagine and glutamine. The experimental enthalpy of the dimer formation derived from the van't Hoff plot is ?59.5 ± 3.8 kJ mol?1. The value is higher than interaction energies between acrylamide and other nucleic acid bases which were determined to be ?57.0 for 1-methylcytosine, ?52.0 for 9-methyladenine, and ?40.6 kJ mol?1 for 1-methyl-uracil. In total, eight hydrogen bonded dimers formed by the three lowest energy 9-methylguanine tautomers and acrylamide were found in the quantum chemical calculations performed at the DFT/B3LYP/6-31++G?? and MP2/6-31++G?? levels of theory. The relative stability and the interaction energies of the dimers were calculated accounting for the basis set superposition error and the zero-point vibrational energy correction. The lowest energy dimer found in the calculations is formed by acrylamide (Ac) with the keto tautomer of 9-methylguanine (Gk). It is stabilized by two intermolecular H bonds, C6=O(Gk) · · · H—N(Ac) and Nl—H(Gk) · · ·O(Ac), and it is more stable than the second lowest energy dimer by ≈ 25 kJ mol?1. The calculated interaction energies of the lowest energy 9-methylguanine-acrylamide dimer are ?65.0 kJ mol?1 and ?67.7 kJ mol?1 at the MP2 and DFT levels of theory, respectively. The experimental enthalpy of the dimer formation is in good agreement with both the calculated interaction energies of the GkAc dimer and much higher than the interaction energies calculated for all other 9-methylguanine-acrylamide dimers. This proved that only one dimer was present in the experimental samples. To verify whether acrylamide is a good model of the amino acid-amide group, we performed direct calculations of the 9-methylguanine-glutamine dimers at the same levels of theory as used for the complexes involving acrylamide. The interaction energies found for the lowest energy 9-methylguanine-glutamine dimer are ?65.1 kJ mon?1 (MP2/6-31++G??) and ?66.2 kJ mol?1 (DFT/B3LYP/6-31++G??) and these values are very close (within 0.5 kJ mol?1) to the interaction energies obtained for the 9-methylguanine-acrylamide dimers. 相似文献
18.
Analysis of combustion regimes and conditional statistics of autoigniting turbulent n-heptane sprays
DNS is performed for a statistically one dimensional layer of a spray region resembling diesel engine conditions. The group and collective combustion regimes are identified according to the ratio of the chemical and transport time scales for a single droplet. The statistics in group combustion are similar with those in gas phase combustion. The collective combustion regime involves interspersed rich regions with different dissipation characteristics. Reasonable agreements are shown with the scaled AMC model and the linear evaporation model in the ranges of meaningful probability. Initially the evaporation terms are dominant in the budgets of the conditional enthalpy equation. After ignition the chemical reaction term becomes dominant to be balanced by the time rate of change term. For modeling turbulent spray combustion it may not be essential to consider detailed micro structures around each droplet, unless in the droplet combustion regime. 相似文献
19.
Lattice potential energy and standard molar enthalpy in the formation of 1-dodecylamine hydrobromide (1-C12H25NH3 ·Br)(s) 下载免费PDF全文
This paper reports that 1-dodecylamine hydrobromide (1--C12H25NH3·Br)(s) has been synthesized using the liquid phase reaction method. The lattice potential energy of the compound 1--C12H25NH3·Br and the ionic volume and radius of the 1--C12H25NH3+ cation are obtained from the crystallographic data and other auxiliary thermodynamic data. The constant-volume energy of combustion of 1--C12H25NH3·Br(s) is measured to be Δc Umo(1--C12H25NH3·Br, s) =--(7369.03±3.28) kJ·mol-1 by means of an RBC-II precision rotating-bomb combustion calorimeter at T=(298.15±0.001) K. The standard molar enthalpy of combustion of the compound is derived to be Δc Hmo(1--C12H25NH3·Br, s)=--(7384.52±3.28) kJ·mol - 1 from the constant-volume energy of combustion. The standard molar enthalpy of formation of the compound is calculated to be Δf Hmo(1--C12H25NH3·Br, s)=--(1317.86±3.67) kJ·mol-1 from the standard molar enthalpy of combustion of the title compound and other auxiliary thermodynamic quantities through a thermochemical cycle. 相似文献