The Experts below are selected from a list of 4497 Experts worldwide ranked by ideXlab platform
L Fournaison - One of the best experts on this subject based on the ideXlab platform.
-
phase equilibrium and Dissociation Enthalpy for semi clathrate hydrate of co2 tbab
Fluid Phase Equilibria, 2008Co-Authors: A Delahaye, L FournaisonAbstract:The present work investigates equilibrium conditions and Dissociation Enthalpy of hydrates formed from CO2-TBAB(tetra-n-butylammonium bromide)-water mixtures. Differential Thermal Analysis (DTA) was used for Hydrate-Liquid-Vapour (H-L-V) equilibrium condition determination in a TBAB concentration range from 4.43 to 9.01 wt% and in a CO2 pressure range from 0.3 to 2.5 MPa. The results showed that the presence of TBAB allowed decreasing the formation pressure of CO2 hydrate by approximately 74 and 87% at 283 and 279 K, respectively. Moreover, pressure reductions were dependent on the TBAB concentration. The Dissociation Enthalpy and the composition of double hydrate formed from 9.01 wt% TBAB solution were determined by both the DTA and Clapeyron equation. The DTA method resulted in 313.2 kJ per kg of hydrate for the Dissociation Enthalpy and 2.51CO2∙TBAB∙38H2O for composition of the double hydrate. For the use of Clapeyron equation, the volume change was defined by taking into account the gas solubility in the liquid phase. The calculation results showed a discrepancy with the experimental data obtained by DTA, suggesting the limited application of Clapeyron equation in the CO2-TBAB-water system.
-
Phase equilibrium and Dissociation Enthalpy for semi-clathrate hydrate of CO2+TBAB
Fluid Phase Equilibria, 2008Co-Authors: Wei Lin, A Delahaye, L FournaisonAbstract:The present work investigates equilibrium conditions and Dissociation Enthalpy of hydrates formed from CO2-TBAB(tetra-n-butylammonium bromide)-water mixtures. Differential Thermal Analysis (DTA) was used for Hydrate-Liquid-Vapour (H-L-V) equilibrium condition determination in a TBAB concentration range from 4.43 to 9.01 wt% and in a CO2 pressure range from 0.3 to 2.5 MPa. The results showed that the presence of TBAB allowed decreasing the formation pressure of CO2 hydrate by approximately 74 and 87% at 283 and 279 K, respectively. Moreover, pressure reductions were dependent on the TBAB concentration. The Dissociation Enthalpy and the composition of double hydrate formed from 9.01 wt% TBAB solution were determined by both the DTA and Clapeyron equation. The DTA method resulted in 313.2 kJ per kg of hydrate for the Dissociation Enthalpy and 2.51CO2∙TBAB∙38H2O for composition of the double hydrate. For the use of Clapeyron equation, the volume change was defined by taking into account the gas solubility in the liquid phase. The calculation results showed a discrepancy with the experimental data obtained by DTA, suggesting the limited application of Clapeyron equation in the CO2-TBAB-water system.
-
Phase equilibrium and Dissociation Enthalpy for semi-clathrate hydrate of CO2 + TBAB
Fluid Phase Equilibria, 2007Co-Authors: Wei Lin, A Delahaye, L FournaisonAbstract:The present work investigates equilibrium conditions and Dissociation Enthalpy of hydrates formed from CO2-TBAB(tetra-n-butylammonium bromide)-water mixtures. Differential Thermal Analysis (DTA) was used for Hydrate-Liquid-Vapour (H-L-V) equilibrium condition determination in a TBAB concentration range from 4.43 to 9.01 wt% and in a CO2 pressure range from 0.3 to 2.5 MPa. The results showed that the presence of TBAB allowed decreasing the formation pressure of CO2 hydrate by approximately 74 and 87% at 283 and 279 K, respectively. Moreover, pressure reductions were dependent on the TBAB concentration. The Dissociation Enthalpy and the composition of double hydrate formed from 9.01 wt% TBAB solution were determined by both the DTA and Clapeyron equation. The DTA method resulted in 313.2 kJ per kg of hydrate for the Dissociation Enthalpy and 2.51CO2∙TBAB∙38H2O for composition of the double hydrate. For the use of Clapeyron equation, the volume change was defined by taking into account the gas solubility in the liquid phase. The calculation results showed a discrepancy with the experimental data obtained by DTA, suggesting the limited application of Clapeyron equation in the CO2-TBAB-water system.
José A. Martinho Simões - One of the best experts on this subject based on the ideXlab platform.
-
O–H Bond Dissociation enthalpies in hydroxyphenols: A time-resolved photoacoustic calorimetry and quantum chemistry study
Phys. Chem. Chem. Phys., 2004Co-Authors: Catarina Correia, Rita C. Guedes, Rui M. Borges Dos Santos, Benedito J. Costa Cabral, José A. Martinho SimõesAbstract:Time-resolved photoacoustic calorimetry (TR-PAC) was used to investigate the energetics of O–H bonds of phenol, catechol, pyrogallol, and phloroglucinol. Values of −27.1 ± 3.9, −44.1 ± 4.4 and −1.6 ± 3.8 kJ mol−1, respectively, were obtained for the solution-phase (acetonitrile) O–H bond Dissociation enthalpies of the last three compounds relative to the O–H bond Dissociation Enthalpy in phenol, ΔDHosln(ArO–H) = DHosln(ArO–H) − DHosln(PhO–H). A value of 388.7 ± 3.7 kJ mol−1 was determined for the PhO–H bond Dissociation Enthalpy in acetonitrile. Density functional theory (MPW1PW91/aug-cc-pVDZ) calculations and complete basis set (CBS-4M) calculations were carried out to analyse intramolecular hydrogen bonding and to predict gas-phase O–H bond Dissociation enthalpies, DHo(ArO–H). A microsolvation model, based on the DFT calculations, was used to study the differential solvation of the phenols and their radicals in acetonitrile and to bridge solution- and gas-phase data. The results strongly suggest that ΔDHosln(ArO–H) ≈ ΔDHo(ArO–H). Hence, to calculate absolute gas-phase O–H bond Dissociation enthalpies in substituted phenols from the corresponding solution-phase values, the solvation enthalpies of the substituted phenols and their radicals are not required.
-
S−H Bond Dissociation Enthalpies in Thiophenols: A Time-Resolved Photoacoustic Calorimetry and Quantum Chemistry Study†
The Journal of Physical Chemistry A, 2002Co-Authors: Rui M. Borges Dos Santos, Rita C. Guedes, Vania S. F. Muralha, Catarina Correia, Benedito J. Costa Cabral, José A. Martinho SimõesAbstract:Time-resolved photoacoustic calorimetry (TR-PAC) and quantum chemistry calculations were used to investigate the energetics of sulfur-hydrogen bonds in thiophenol and four para-substituted thiophenols, 4-XC 6 H 4 SH (X = CH 3 , OCH 3 , Cl, and CF 3 ). The result obtained for the PhS-H gas-phase bond Dissociation Enthalpy, derived from the PAC experimental results in solution, is 349.4 ′ 4.5 kJ mol - 1 . This value is significantly higher than recent literature values but agrees with a value suggested some 20 years ago in a widely used review. The PAC result also concurs with the value computed at a high theory level, G3(MP2), 346.8 kJ mol - 1 . The data obtained for the substituted thiophenols support the idea that substituent effects are less pronounced on the S-H bond Dissociation Enthalpy than on the O-H bond Dissociation Enthalpy of the corresponding phenols.
-
Uranium-ligand bond-Dissociation enthalpies of uranium(IV) poly(pyrazolyl)borate complexes
J. Chem. Soc. Dalton Trans., 1994Co-Authors: João Paulo Leal, José A. Martinho SimõesAbstract:Solution calorimetry measurements involving the complexes [UCl2L{HB(dmpz)3}](L = OCMe2CH2COMe or dmpz; dmpz = 3,5-dimethylpyrazol-1 -yl) led to D(U–OCMe2CH2COMe) and D(U–dmpz) bond-Dissociation enthalpies of 484.2 ± 8.6 and 393 ± 16 kJ mol–1 in solution. The fact that the uranium–ligand bond-Dissociation Enthalpy in the L = OCMe2CH2COMe complex is about 20 kJ mol–1 higher than D(U–O) values observed for other complexes of the same type is consistent with a bidentate co-ordination of the ligand to the metal centre. This conclusion relies on literature data and on equilibrium studies in solution involving the complex [UCl3{HB(dmpz)3}]·OC4H8, which afforded the U–OC4H8 bond-Dissociation Enthalpy, 21.5 ± 2.9 kJ mol –1.
Rita C. Guedes - One of the best experts on this subject based on the ideXlab platform.
-
O–H Bond Dissociation enthalpies in hydroxyphenols: A time-resolved photoacoustic calorimetry and quantum chemistry study
Phys. Chem. Chem. Phys., 2004Co-Authors: Catarina Correia, Rita C. Guedes, Rui M. Borges Dos Santos, Benedito J. Costa Cabral, José A. Martinho SimõesAbstract:Time-resolved photoacoustic calorimetry (TR-PAC) was used to investigate the energetics of O–H bonds of phenol, catechol, pyrogallol, and phloroglucinol. Values of −27.1 ± 3.9, −44.1 ± 4.4 and −1.6 ± 3.8 kJ mol−1, respectively, were obtained for the solution-phase (acetonitrile) O–H bond Dissociation enthalpies of the last three compounds relative to the O–H bond Dissociation Enthalpy in phenol, ΔDHosln(ArO–H) = DHosln(ArO–H) − DHosln(PhO–H). A value of 388.7 ± 3.7 kJ mol−1 was determined for the PhO–H bond Dissociation Enthalpy in acetonitrile. Density functional theory (MPW1PW91/aug-cc-pVDZ) calculations and complete basis set (CBS-4M) calculations were carried out to analyse intramolecular hydrogen bonding and to predict gas-phase O–H bond Dissociation enthalpies, DHo(ArO–H). A microsolvation model, based on the DFT calculations, was used to study the differential solvation of the phenols and their radicals in acetonitrile and to bridge solution- and gas-phase data. The results strongly suggest that ΔDHosln(ArO–H) ≈ ΔDHo(ArO–H). Hence, to calculate absolute gas-phase O–H bond Dissociation enthalpies in substituted phenols from the corresponding solution-phase values, the solvation enthalpies of the substituted phenols and their radicals are not required.
-
S−H Bond Dissociation Enthalpies in Thiophenols: A Time-Resolved Photoacoustic Calorimetry and Quantum Chemistry Study†
The Journal of Physical Chemistry A, 2002Co-Authors: Rui M. Borges Dos Santos, Rita C. Guedes, Vania S. F. Muralha, Catarina Correia, Benedito J. Costa Cabral, José A. Martinho SimõesAbstract:Time-resolved photoacoustic calorimetry (TR-PAC) and quantum chemistry calculations were used to investigate the energetics of sulfur-hydrogen bonds in thiophenol and four para-substituted thiophenols, 4-XC 6 H 4 SH (X = CH 3 , OCH 3 , Cl, and CF 3 ). The result obtained for the PhS-H gas-phase bond Dissociation Enthalpy, derived from the PAC experimental results in solution, is 349.4 ′ 4.5 kJ mol - 1 . This value is significantly higher than recent literature values but agrees with a value suggested some 20 years ago in a widely used review. The PAC result also concurs with the value computed at a high theory level, G3(MP2), 346.8 kJ mol - 1 . The data obtained for the substituted thiophenols support the idea that substituent effects are less pronounced on the S-H bond Dissociation Enthalpy than on the O-H bond Dissociation Enthalpy of the corresponding phenols.
-
Thermochemical Properties and Structure of Phenol-(H2O)1-6and Phenoxy-(H2O)1-4by Density Functional Theory
The Journal of Physical Chemistry A, 2000Co-Authors: Rita C. Guedes, B. J. Costa Cabral, J. A. Martinho Simoes, Hermínio P. DiogoAbstract:Structural, vibrational, and thermochemical properties of phenol−(H2O)1-6 and phenoxy radical−(H2O)1-4 complexes were calculated by using density functional theory. The insertion of a phenol molecule in a water cluster keeps some similarities with the addition of a water molecule. The interaction of the phenoxy radical with water clusters shows a strong dependence on the cluster size. The results are compared with theoretical and experimental data for the vibrational structure of phenol−water complexes and with thermochemical data for the phenol O−H bond Dissociation Enthalpy.
William E. Acree - One of the best experts on this subject based on the ideXlab platform.
-
thermochemistry of 2 amino 3 quinoxalinecarbonitrile 1 4 dioxide evaluation of the mean Dissociation Enthalpy of the n o bond
Organic and Biomolecular Chemistry, 2004Co-Authors: Maria Ribeiro D M C Da Silva, Jose R B Gomes, Jorge M Goncalves, Emanuel A Sousa, Siddharth Pandey, William E. AcreeAbstract:The standard Enthalpy of formation of the 2-amino-3-quinoxalinecarbonitrile-1,4-dioxide compound in the gas-phase was derived from the enthalpies of combustion of the crystalline solid measured by static bomb combustion calorimetry and its Enthalpy of sublimation determined by Knudsen mass-loss effusion at T = 298.15 K. This value is (383.8 ± 5.4) kJ mol−1 and was subsequently combined with the experimental gas-phase Enthalpy of formation of atomic oxygen and with the computed gas-phase Enthalpy of formation of 2-amino-3-quinoxalinecarbonitrile, (382.0 ± 6.3) kJ mol−1, in order to estimate the mean (N–O) bond Dissociation Enthalpy in the gas-phase of 2-amino-3-quinoxalinecarbonitrile-1,4-dioxide. The result obtained is (248.3 ± 8.3) kJ mol−1, which is in excellent agreement with the B3LYP/6-311+G(2d,2p)//B3LYP/6-31G(d) computed value.
-
experimental and theoretical study of the Dissociation Enthalpy of the n o bond on 2 hydroxypyridine n oxide theoretical analysis of the energetics of the n o bond for hydroxypyrydine n oxide isomers
The Journal of Chemical Thermodynamics, 2004Co-Authors: Maria Ribeiro D M C Da Silva, Margarida S. Miranda, Agostinha M R Matos, Victor M F Morais, William E. AcreeAbstract:Abstract The standard ( p ∘ =0.1 MPa) molar Enthalpy of formation of crystalline 2-hydroxypyridine N -oxide was measured, at T =298.15 K, by static bomb calorimetry and the standard molar Enthalpy of sublimation, at T =298.15 K, was obtained using Calvet microcalorimetry. These values were used to derive the standard molar Enthalpy of formation of 2-hydroxypyridine N -oxide in gaseous phase, and to evaluate the Dissociation Enthalpy of the N–O bond. Additionally, high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional have been performed for the three isomers of hydroxypyridine N -oxide in order to confirm the experimental trend for the Dissociation Enthalpy of the (N–O) bond.
-
energetics of 6 methoxyquinoline and 6 methoxyquinoline n oxide the Dissociation Enthalpy of the n o bond
The Journal of Chemical Thermodynamics, 2003Co-Authors: Maria Ribeiro D M C Da Silva, Ana L.r. Silva, Óscar O. P. Fernandes, Luis M N B F Santos, William E. AcreeAbstract:Abstract The standard (p o =0.1 MPa ) molar enthalpies of formation, at T=298.15 K , were determined using static-bomb calorimetry for crystalline 6-methoxyquinoline N -oxide (6MeOQUINO), as −(85.6±3.7) kJ · mol −1 and liquid 6-methoxyquinoline (6MeOQUI), −(25.8±2.2) kJ · mol −1 . The standard molar enthalpies of sublimation/vaporization, at T=298.15 K , were measured by microcalorimetry and from the enthalpies of formation of the gaseous compounds, the Dissociation Enthalpy D m 0 of the (N + –O − ) dative covalent bond was derived, as (269.2±5.0) kJ · mol −1 .
-
enthalpies of combustion of 2 iodosobenzoic acid and 4 nitrosophenol the Dissociation Enthalpy of the i o bond
The Journal of Chemical Thermodynamics, 1999Co-Authors: M Ribeiro D M C Da Silva, M. A. R. Matos, Maria Luísa C.c.h. Ferrão, Luísa M.p.f. Amaral, Margarida S. Miranda, William E. Acree, G PilcherAbstract:Article on the enthalpies of combustion of 2-iodosobenzoic acid and 4-nitrosophenol and the Dissociation Enthalpy of the I-O bond.
-
Enthalpies of combustion of 2-iodosobenzoic acid and 4-nitrosophenol: the Dissociation Enthalpy of the I–O bond
The Journal of Chemical Thermodynamics, 1999Co-Authors: M. D. M. C. Ribeiro Da Silva, M. A. R. Matos, Maria Luísa C.c.h. Ferrão, Luísa M.p.f. Amaral, Margarida S. Miranda, William E. Acree, Geoffrey PilcherAbstract:Article on the enthalpies of combustion of 2-iodosobenzoic acid and 4-nitrosophenol and the Dissociation Enthalpy of the I-O bond.
Peter Mulder - One of the best experts on this subject based on the ideXlab platform.
-
comment on the Enthalpy of the o h homolytic Dissociation basis set extrapolated density functional theory and coupled cluster calculations by b j costa cabral and s canuto chem phys lett 406 2005 300 305
Chemical Physics Letters, 2006Co-Authors: Gino A Dilabio, Peter MulderAbstract:Abstract Costa Cabral and Canuto [B.J. Costa Cabral, S. Canuto, Chem. Phys. Lett. 406 (2005) 300] have studied the O–H bond Dissociation Enthalpy in water, hydrogen peroxide, methanol, phenol and catechol using a number of theoretical methods. Their choice of experimental O–H bond Dissociation enthalpies for phenol and catechol are not the best available values and led them to several erroneous conclusions about the performance of methodologies they tested. In this work, we present more rigorous experimental O–H bond Dissociation enthalpies for phenol and catechol and discuss the implications these data have on the conclusions presented by Costa Cabral and Canuto. We also demonstrate the importance of the inclusion of higher-order excitations in the coupled-cluster treatment of bond Dissociation Enthalpy of the O–H bond in H 2 O 2 and HOO .
-
critical re evaluation of the o h bond Dissociation Enthalpy in phenol
Journal of Physical Chemistry A, 2005Co-Authors: Peter Mulder, Gian Franco Pedulli, Hansgert Korth, Derek A Pratt, Gino A Dilabio, Luca Valgimigli, K U IngoldAbstract:The gas-phase O−H bond Dissociation Enthalpy, BDE, in phenol provides an essential benchmark for calibrating the O−H BDEs of other phenols, data which aids our understanding of the reactivities of phenols, such as their relevant antioxidant activities. In a recent review, the O−H BDE for phenol was presented as 90 ± 3 kcal mol-1 (Acc. Chem. Res. 2003, 36, 255−263). Due to the large margin of error, such a parameter cannot be used for dynamic interpretations nor can it be used as an anchor point in the development of more advanced computational models. We have reevaluated the existing experimental gas-phase data (thermolyses and ion chemistry). The large errors and variations in thermodynamic parameters associated with the gas-phase ion chemistry methods produce inconsistent results, but the thermolytic data has afforded a value of 87.0 ± 0.5 kcal mol-1. Next, the effect of solvent has been carefully scrutinized in four liquid-phase methods for measuring the O−H BDE in phenol: photoacoustic calorimetry, o...
-
Substituent effects on the benzylic bond Dissociation Enthalpy in benzyl bromides (C–Br) and tert-butylbenzenes (C–CH3): a gas phase thermolysis and liquid phase photoacoustic study
Journal of the Chemical Society Perkin Transactions 2, 1997Co-Authors: Lucas J. J. Laarhoven, Jan Born, Isabel W. C. E. Arends, Peter MulderAbstract:The bond Dissociation enthalpies in a number of substituted benzyl bromides have been studied in the gas phase, using the toluene carrier technique, and in solution with photoacoustic calorimetry. Gas phase thermolysis with unsubstituted benzyl bromide gives an absolute C–Br bond Dissociation Enthalpy (Ed) at 298 K of 255 ± 4 kJ mol–1. Competition experiments in the gas phase reveal no substituent effect on the value of Ed(C–Br). Gas phase thermolysis with substituted tert-butylbenzenes also shows no effect on the C–CH3 bond Dissociation Enthalpy for p-CN, p-OH and p-But substituents, with a Ed(C–CH3) value at 298 K of 299 ± 2 kJ mol–1. In solution, photoacoustic experiments yield no detectable substituent effect for p-CN, p-But and m-CF3 substitution of the benzyl bromide, in contrast with other reports. With photoacoustic calorimetry a bond Dissociation Enthalpy of 254 ± 4 kJ mol–1 has been found for all benzyl bromides studied. A rationale for the absence of a substituent effect on the benzylic bond Dissociation Enthalpy is provided.
-
substituent effects on the benzylic bond Dissociation Enthalpy in benzyl bromides c br and tert butylbenzenes c ch3 a gas phase thermolysis and liquid phase photoacoustic study
Journal of The Chemical Society-perkin Transactions 1, 1997Co-Authors: Lucas J. J. Laarhoven, Jan Born, Isabel W. C. E. Arends, Peter MulderAbstract:The bond Dissociation enthalpies in a number of substituted benzyl bromides have been studied in the gas phase, using the toluene carrier technique, and in solution with photoacoustic calorimetry. Gas phase thermolysis with unsubstituted benzyl bromide gives an absolute C–Br bond Dissociation Enthalpy (Ed) at 298 K of 255 ± 4 kJ mol–1. Competition experiments in the gas phase reveal no substituent effect on the value of Ed(C–Br). Gas phase thermolysis with substituted tert-butylbenzenes also shows no effect on the C–CH3 bond Dissociation Enthalpy for p-CN, p-OH and p-But substituents, with a Ed(C–CH3) value at 298 K of 299 ± 2 kJ mol–1. In solution, photoacoustic experiments yield no detectable substituent effect for p-CN, p-But and m-CF3 substitution of the benzyl bromide, in contrast with other reports. With photoacoustic calorimetry a bond Dissociation Enthalpy of 254 ± 4 kJ mol–1 has been found for all benzyl bromides studied. A rationale for the absence of a substituent effect on the benzylic bond Dissociation Enthalpy is provided.