共查询到20条相似文献,搜索用时 10 毫秒
1.
Matos MA Miranda MS Monte MJ Santos LM Morais VM Chickos JS Umnahanant P Liebman JF 《The journal of physical chemistry. A》2007,111(43):11153-11159
Condensed phase standard (p degrees = 0.1 MPa) molar enthalpies of formation for 1-indanone, 2-indanone, and 1,3-indandione were derived from the standard molar enthalpies of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The standard molar enthalpies of sublimation for 1-indanone and 2-indanone, at T = 298.15 K, were measured both by correlation-gas chromatography and by Calvet microcalorimetry leading to a mean value for each compound. For 1,3-indandione, the standard molar enthalpy of sublimation was derived from the vapor pressure dependence on temperature. The following enthalpies of formation in gas phase, at T = 298.15 K, were then derived: 1-indanone, -64.0 +/- 3.8 kJ mol(-1); 2-indanone, -56.6 +/- 4.8 kJ mol(-1); 1,3-indandione, -165.0 +/- 2.6 kJ mol(-1). The vaporization and fusion enthalpies of the indanones studied are also reported. In addition, theoretical calculations using the density functional theory with the B3LYP and MPW1B95 energy functionals and the 6-311G** and cc-pVTZ basis sets have been performed for these molecules and the corresponding one-ring species to obtain the most stable geometries and to access their energetic stabilities. 相似文献
2.
Roux MV Jiménez P Dávalos JZ Notario R Juaristi E 《The Journal of organic chemistry》2001,66(16):5343-5351
To understand the differences in conformational behavior and reactivity of oxygen- and sulfur-containing 1,3,5-heterocyclohexanes, the enthalpies of formation and sublimation of 1,3,5-trithiane, 1, have been measured. The numerical value of the enthalpy of formation for this compound in the solid state is -8.6 +/- 2.6 kJ mol(-1), while the corresponding value in the gaseous state is 84.6 +/- 2.6 kJ mol(-1). The value for the enthalpy of sublimation is 93.2 +/- 0.2 kJ mol(-1). Standard ab initio molecular orbital calculations at the G2(MP2), G2, and G3 levels were performed, and the calculated enthalpies of formation are compared with the experimental data. These experimental and theoretical studies support the relevance of through-space lone pair-lone pair electronic repulsion in the sulfur heterocycle. 相似文献
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Thermochemical data, and in particular the enthalpies of formation of oxygen- and sulfur-containing six-membered heterocycles provide essential information on the factors responsible for the contrasting behavior (structural, conformational and reactivity) between these types of compounds. A proper understanding of the experimental observations requires theoretical modeling in order to confirm the relative importance of the steric, electronic, electrostatic and stereoelectronic interactions that are responsible of the enthalpies of formation for the heterocyclic compounds of interest. 相似文献
5.
Ribeiro da Silva MA Lobo Ferreira AI Cimas Á 《The Journal of organic chemistry》2011,76(10):3754-3764
Thermodynamic properties of 3- and 4-phenoxyphenol have been determined by using a combination of calorimetric and effusion techniques as well as by high-level ab initio molecular orbital calculations. The standard (p° = 0.1 MPa) molar enthalpies of formation in the condensed and gas states, Δ(f)H(m)°(cr or l) and Δ(f)H(m)°(g), at T = 298.15 K, of 3- and 4-phenoxyphenol were derived from their energies of combustion in oxygen, measured by a static bomb calorimeter, and from the enthalpies of vaporization or sublimation derived respectively by Calvet microcalorimetry for the 3-phenoxyphenol and by Knudsen effusion technique for the 4-phenoxyphenol. The theoretically estimated gas-phase enthalpies of formation were calculated from high-level ab initio molecular orbital calculations at the G3(MP2)//B3LYP level of theory. Furthermore, this composite approach was also used to obtain information about the gas-phase acidities, gas-phase basicities, proton and electron affinities, adiabatic ionization enthalpies, and, finally, O?H bond dissociation enthalpies. The good agreement between the G3MP2B3-derived values and the experimental gas-phase enthalpies of formation for the 3- and 4-phenoxyphenol gives confidence to the estimate concerning the 2-phenoxyphenol isomer, which was not experimentally studied, and to the estimates concerning the radical and the anion. Additionally, the experimental values of gas-phase enthalpies of formation were also compared with estimates based on the empirical scheme developed by Cox. 相似文献
6.
Roux MV Temprado M Jiménez P Notario R Guzman-Mejía R Juaristi E 《The Journal of organic chemistry》2007,72(4):1143-1147
The enthalpies of formation in the condensed and gas states, DeltafH degrees m(cd) and DeltafH degrees m(g), of 1,3- and 1,4-oxathiane sulfones were derived from their respective enthalpies of combustion in oxygen, measured by a rotating bomb calorimeter and the variation of vapor pressures with temperatures determined by the Knudsen effusion technique. Standard ab initio molecular orbital calculations at the G2(MP2) and G3 levels were performed, and a theoretical study on molecular and electronic structure of the compounds has been carried out. Calculated DeltafH degrees m(g) values at the G3 level using atomization reactions agree well with the experimental ones. These experimental and theoretical studies support that the destabilization found in 1,3-oxathiane sulfone, 11.2 kJ mol-1 respecting to 1,4-oxathiane sulfone, is due to the electrostatic repulsion between the negative charges of the axial oxygen of the sulfone and the oxygen of the ring and apparently masks any stabilization originating from the hyperconjugative nO --> sigma*C-SO2 stereoelectronic interaction. 相似文献
7.
Roux MV Temprado M Jiménez P Notario R Guzman-Mejía R Juaristi E 《The Journal of organic chemistry》2006,71(7):2581-2586
This work reports the enthalpies of formation in the condensed and gas state of 1,4-dithiacyclohexane 1,1-dioxide (1,4-dithiane sulfone, 5), derived from the enthalpy of combustion in oxygen, measured by a rotating bomb calorimeter and the variation of vapor pressures with temperatures determined by the Knudsen effusion technique. The theoretically estimated enthalpy of formation was calculated from high-level ab initio molecular orbital calculations at the G2(MP2) level. The theoretical calculations appear to be in very good agreement with experiment. A comparison of the conversion of thiane sulfone 3 to 1,3-dithiane sulfone 4 and 1,4-dithiane sulfone 5 clearly shows the 1,3 isomer to be 6.7 kJ mol(-1) less stable, probably owing to diminished electrostatic repulsion between the sulfur heteroatoms in 1,4-sulfone 5. 相似文献
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Roux MV Temprado M Jiménez P Notario R Guzmán-Mejía R Juaristi E 《The Journal of organic chemistry》2004,69(5):1670-1675
The enthalpies of combustion and sublimation of 1,3-dithiacyclohexane 1,1-dioxide (1,3-dithiane sulfone) were measured by a rotating-bomb combustion calorimeter and the Knudsen effusion technique, and the gas-phase enthalpy of formation was determined, Delta(f)H(m)*(g) = -326.3 +/- 2.0 kJ mol(-1). Standard ab initio molecular orbital calculations at the G2(MP2) level were performed, and a theoretical study on molecular and electronic structure of the compound has been carried out. Calculated Delta(f)H(m)*(g) values agree very well with the experimental one. These experimental and theoretical studies support the relevance of the repulsive electrostatic interaction between sulfur atoms in 1,3-dithiane sulfone, that apparently counterbalances any n(S) --> rho(C-SO2)* stabilizing hyperconjugative interaction. 相似文献
10.
Matos MA Miranda MS Fonseca DA Morais VM Liebman JF 《The journal of physical chemistry. A》2008,112(40):10053-10058
The standard (p(o) = 0.1 MPa) molar energies of combustion in oxygen, at T = 298.15 K, of solid 3,3-tetramethyleneglutaric acid and the related 3,3-tetramethyleneglutaric anhydride and 3,3-tetramethyleneglutarimide were measured by static bomb combustion calorimetry. The values of the standard molar enthalpies of sublimation, at T = 298.15 K, were obtained by Calvet microcalorimetry, allowing the calculation of the standard molar enthalpies of formation of the compounds, in the gaseous state, at T = 298.15 K. The geometries of the experimentally studied compounds were fully optimized using density functional theory with the B3LYP functional and extended basis sets. More accurate energies were also obtained from single-point calculations at the most stable B3LYP/6-311G** geometries, using the cc-pVTZ basis set. From these calculations the standard molar enthalpies of formation of 3,3-tetramethyleneglutaric acid, 3,3-tetramethyleneglutaric anhydride, and 3,3-tetramethyleneglutarimide were estimated using isodesmic reactions involving glutaric acid, glutaric anhydride, and glutarimide, respectively. Experimental and computational results were used in the discussion of the interrelation of energetics and structure in these compounds and compared with other structurally related compounds. 相似文献
11.
Enthalpy increment measurements on melts in the system KF-K2TaF7 were carried out by drop calorimetry at temperatures between 298 K and 1063, 1103 and 1143 K for selected compositions. Heat
capacities of the melted mixtures and enthalpies of mixing have been determined. Careful calorimetric experiments showed small
but distinct non-ideality of the melt. The molar heat capacity of melt exhibits small positive divergence from additivity.
The molar enthalpy of mixing shows negative deviation from ideality which decreases with increasing temperature. The thermal
effect at mixing was assigned predominantly to association reactions producing more complex fluorotantalate anions. The formation
of complex anions with lower coordination number of Ta may not be excluded.
相似文献
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Hiroyuki Yoshida Takushi Ito Akira Murata 《Fresenius' Journal of Analytical Chemistry》1990,338(6):738-740
Summary The acid dissociation constant of 4-methyl-6-acetyl-7-hydroxycoumarin, as determined by spectrophotometry was found to be Ka=9.77×10–9. Beryllium reacts with this reagent to form a water-insoluble complex that can be extracted into benzene. The maximum wavelengths of the excitation and emission spectra of the beryllium complex in benzene are 403 and 465 nm, respectively. Beryllium can be determined in the range 0.0050.1 g per 10 ml benzene when extracted from the solution at pH 7.57.8 into benzene. 相似文献
14.
Kočí J Grandclaude V Massonneau M Richard JA Romieu A Renard PY 《Chemical communications (Cambridge, England)》2011,47(23):6713-6715
Synthesis and chemiluminescent properties of a new 1,2-dioxetane chemiluminophore bearing a 7-hydroxycoumarin moiety are presented. The 1,2-dioxetane decomposition ended up with strong and long-lived emission of light. This new structure opens way to the development of a new generation of bright chemiluminescent bio-probes. 相似文献
15.
Ya. V. Voznyi M. O. Dekaprilevich D. S. Yufit Yu. T. Struchkov 《Russian Chemical Bulletin》1992,41(6):1072-1075
A method was developed for the production of derivatives of 4-trifluoromethyl-7-hydroxycoumarin with electron-withdrawing groups (CN, CF3CO) at position 3. The structure of 3-cyano-4-trifluoromethyl-7-acetoxycoumarin was proved by x-ray crystallographic investigation. The effect of the substituents on the geometry of the molecule is discussed.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. A. N. Nesmeyanov Institute of Heteroorganic Compounds, Russian Academy of Sciences, 117813 Moscow. Institute of Biochemistry, Academy of Sciences of Armenia, 375044 Erevan. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 6, pp. 1371–1375, June, 1992. 相似文献
16.
Derivatives of 4-methylumbelliferone (4-methyl-7-hydroxycoumarin) are important fluorogenic substrates for the assay of group-specific hydrolases and in enzyme-linked immunoassays. The development of techniques suitable for the low-temperature phosphorimetric detection and determination of such derivatives on thin-layer chromatograms is described. 相似文献
17.
Gnül YENLMEZ FT Sergen YILMAZ Nagihan BAYIK Elif ENKUYTU Esra Nur KAYA Mahmut DURMU Mustafa BULUT 《Turkish Journal of Chemistry》2020,44(1):64
The newly synthesized cyclotriphosphazene cored coumarin chemosensors 5, 6, and 7 were successfully characterized by 1 H NMR, 31 P NMR, and MALDI-TOF mass spectrometry. Additionally, the photophysical and metal sensing properties of the targeted compounds were determined by fluorescence spectroscopy in the presence of various metals (Li + , Na + , K + , Cs + , Mg 2+ , Ca 2+ , Ba 2+ , Cr 3+ , Mn 2+ , Fe 3+ , Co 2+ , Al 3+ , Hg + , Cu 2+ , Zn 2+ , Ag + , and Cd 2+ ) . The fluorescence titration results showed that compounds 5, 6, and 7 could be employed as fluorescent chemosensors for Fe 3+ ions with high sensitivity. The complex stoichiometry between final cyclotriphosphazene chemosensors and Fe 3+ ions was also determined by Job’s plots. 相似文献
18.
The heat capacity investigation of crystalline pentasodium zirconium tris(phosphate) was carried out in a vacuum adiabatic calorimeter between 7 and 340 K and in a differential scanning calorimeter of the heat bridge type between 330 and 620 K. Between 389 and 424 K, an isostructural solid-to-solid phase transition of Na5Zr(PO4)3, has been found, the nature of which is connected with a centering of off-centered zirconium atoms in octahedral sites and an occupation transfer between sodium sites in the structure. The results were used to calculate the characteristics of the phase transition and the thermodynamic functions of Na5Zr(PO4)3: the transition temperature T°trs, enthalpy of transition ΔtrsH°, entropy of transition ΔtrsS°; enthalpy H°(T)−H°(0), entropy S°(T) and Gibbs function G°(T)−H°(0) over the range from 0 to 620 K. From hydrofluoric acid solution microcalorimetry, the enthalpy of solution of Na5Zr(PO4)3 at 298.15 K has been determined and the standard enthalpy of formation has been derived. By combining the data obtained by the two techniques, the Gibbs function of formation of Na5Zr(PO4)3 at 298.15 K has been calculated. 相似文献
19.
Kanibolotsky D. S. Golovataya N. V. Lisnyak V. V. 《Journal of Thermal Analysis and Calorimetry》2004,76(1):323-327
The enthalpies of mixing of liquid Gd-Si (1770±5 K) and Al-Gd (1760±5 K) alloys have been measured by high-temperature isoperibolic
calorimetry. The calorimetric study of the gadolinium-based liquid alloys demonstrates the great negative enthalpies of mixing,
which is associated with the contribution of GdSi and GdAl2 intermetallides into the liquid-state thermodynamics. The comparison of obtained results with literature data has been performed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
20.
H. Hanabata T. Matsuo H. Suga 《Journal of inclusion phenomena and macrocyclic chemistry》1987,5(3):325-333
Heat capacities of crystalline-cyclodextrin undecahydrate have been measured in the temperature range between 13 and 300K by use of a miniaturized adiabatic low-temperature calorimeter. A first-order phase transition occurred at 226K with a discontinuous entropy change of 45.0 ± 1.0J
K
–1 mol–1. The highly disordered nature of the high temperature phase was considered in relation to the entropy contribution. A glass transition phenomenon observed around 150K was ascribed to the freezing of a configurational change of the protons engaged in the four-membered hydrogen-bonded ring which appeared only in the low temperature phase. 相似文献