Search

Thermochemical and thermodynamic properties of 2-, 3- and 4-iodonitrobenzene have been determined using a combination of calorimetric and effusion techniques as well as computational calculations. The standard (p° = 0.1 MPa) molar enthalpies of formation, in the crystalline state, Δ f H m ∘ (cr) , at T = 298.15 K, were derived from the standard molar enthalpies of combustion, Δ c H m ∘ (cr) , in oxygen, to yield CO2(g), N2(g), and I2(cr), at T = 298.15 K, measured by rotating bomb combustion calorimetry. The standard molar enthalpies of sublimation of these compounds, Δ cr g H m ∘ , at T = 298.15 K, were determined using high temperature Calvet microcalorimetry. The Knudsen mass-loss effusion technique was used to determine the standard molar enthalpies, entropies and Gibbs free energies of sublimation, at T = 298.15 K, of the three studied compounds. The combination of some of the referred thermodynamic parameters yielded the standard (po = 0.1 MPa) molar enthalpies of formation in the gaseous phase, at T = 298.15 K, of the three isomers: Δ f H m ∘ ( 2 - iodonitrobenzene, g ) = (178.8 ± 1.5) kJ · mol - 1 , Δ f H m ∘ ( 3 - iodonitrobenzene, g ) = (155.4 ± 1.8) kJ · mol - 1 and Δ f H m ∘ ( 4 - iodonitrobenzene, g ) = (151.8 ± 1.6) kJ · mol - 1 . The results were analyzed and interpreted in terms of enthalpic increments and molecular structure. Using the empirical scheme developed by Cox, the values of the standard molar enthalpies of formation in the gaseous phase were estimated and afterwards compared with the ones obtained experimentally, being both interpreted in terms of the molecular structure of the compounds. For comparison purposes, standard molecular calculations at the B3LYP6-311++G(d, p) level were performed, and the gas-phase enthalpies of formation of the three compounds were estimated; the results are in good agreement with experimental data. Furthermore, the molecular structures of the three molecules were established and the structural parameters were determined at the B3LYP/6-311++G(d, p) level of theory. The computational study was also extended to the determination of proton and electron affinities, basicities, and adiabatic ionization enthalpies.

The thermochemistry of α-D-xylose(cr) was studied by means of oxygen bomb calorimetry and a Physical Property Measurement System (PPMS) in zero magnetic field. The sample of α-D-xylose(cr) used in this study was one well-characterized by HPLC, Karl Fischer analysis, NMR, and by carbon dioxide analysis. The standard molar enthalpy of combustion was found to be Δc H m o = −(2342.2 ± 0.8) kJ·mol−1 at T = 298.15 K and at the standard pressure p° = 0.1 MPa. The standard molar heat capacity for α-D-xylose(cr) was measured with the PPMS over the temperature range 1.9001 ⩽ T/K ⩽ 303.66. At T = 298.15 K, C p ,m o = (178.1 ± 1.8) J·K−1·mol−1. The values of C p ,m o were fit as a function of T by using theoretical and empirical models for appropriate temperature ranges. The results of these fits were used to calculate values of C p ,m o , the entropy increment Δ 0 T S m o , Δ 0 T H m o , and Φ m o = ( Δ 0 T S m o - Δ 0 T H m o / T ) from T = 0.5 K to T = 300 K. Derived quantities for α-D-xylose(cr) are the standard molar enthalpy of formation Δ f H m o = −(1054.5 ± 1.1) kJ·mol−1, the third law standard molar entropy S m o = (175.3 ± 1.9) J·K−1·mol−1, and the standard molar Gibbs energy of formation Δ f G m o = −(750.5 ± 1.0) kJ·mol−1. A comparison of values of Δc H m o and S m o for the five-carbon aldoses demonstrated a striking similarity in the values of these respective properties for α-D-xylose(cr), D-ribose(cr), and D-arabinose(cr). Thermochemical network calculations were performed that led to values of the standard formation properties at T = 298.15 K for a variety of biochemical substances: D-xylose(aq), D-xylose−(aq), D-xylose2−(aq), D-lyxose(cr and aq), D-lyxose−(aq), D-xylulose(aq), xylitol(aq), 1,4-β-D-xylobiose(am and aq), and 1,4-β-D-xylotriose(am and aq).

The standard ( p ° = 0.1 MPa) molar enthalpies of formation, in the condensed phase, of the three monoiodoanisoles, were derived from the respective enthalpies of combustion, measured by rotating-bomb combustion calorimetry. Their enthalpies of sublimation/vaporization, at T = 298.15 K, were obtained by Calvet microcalorimetry using the high-temperature vacuum sublimation technique. Moreover the standard molar enthalpy, entropy and Gibbs energy of sublimation, at T = 298.15 K, of 4-iodoanisole were derived from the Knudsen mass-loss effusion technique. Combining the former sets of experimental results, the standard molar enthalpies of formation in the gas-phase, at T = 298.15 K, of 2-, 3- and 4-iodoanisole were derived, respectively, as: (15.1 ± 2.1) kJ · mol −1 ; (11.8 ± 2.2) kJ · mol −1 , and (12.4 ± 1.6) kJ · mol −1 . The experimental values of the gas-phase enthalpies of formation of each iodoanisole were also estimated by means of the empirical scheme developed by Cox and by density functional theory calculations employing the B3LYP/6-311++G(d,p) approach. Estimated values are in excellent agreement with the reported experimental ones derived in the present paper.

This paper reports a combined experimental and computational thermochemical study of 4-benzyloxyphenol. Static bomb combustion calorimetry and Knudsen mass-loss effusion technique were used to determine the standard (p° = 0.1 MPa) molar enthalpy of combustion, Δ c H m ∘ = - ( 6580.1 ± 1.8 ) kJ · mol - 1 , and of sublimation, Δ cr g H m ∘ = ( 131.0 ± 0.9 ) kJ · mol - 1 , respectively, from which the standard (p° = 0.1 MPa) molar enthalpy of formation, in the gaseous phase, at T = 298.15 K, Δ f H m ∘ = - ( 119.5 ± 2.7 ) kJ · mol - 1 were derived. For comparison purposes, the gas-phase enthalpy of formation of this compound was estimated by G3(MP2)//B3LYP calculations, using a set of gas-phase working reactions; the results are in excellent agreement with experimental data. G3(MP2)//B3LYP computations were also extended to the calculation of the gas-phase enthalpies of formation of the 2- and 3-benzyloxyphenol isomers. 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 standard (p° = 0.1 MPa) molar enthalpies of formation, in the crystalline state, of the 1- and 2-cyanonaphthalene were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by static-bomb combustion calorimetry. Vapor pressure measurements at different temperatures, using the Knudsen mass loss effusion technique, enabled the determination of the enthalpy, entropy, and Gibbs energy of sublimation, at T = 298.15 K, for both isomers. The standard molar enthalpies of sublimation, at T = 298.15 K, for 1- and 2-cyanonaphthalene, were also measured by high-temperature Calvet microcalorimetry. - Δ c U m ∘ ( cr ) / ( kJ · mol - 1 ) Δ f H m ∘ ( cr ) / ( kJ · mol - 1 ) Δ cr g H m ∘ ( cr ) / ( kJ · mol - 1 ) 1-Cyanonaphthalene 5514.4 ± 1.6 188.5 ± 2.2 88.6 ± 0.5 2-Cyanonaphthalene 5510.5 ± 1.7 184.6 ± 2.2 92.1 ± 0.1 Combining these two experimental values, the gas-phase standard molar enthalpies, at T = 298.15 K, were derived and compared with those estimated by employing two different methodologies: one based on the Cox scheme and the other one based on G3MP2B3 calculations. The calculated values show a good agreement with the experimental values obtained in this work.

This work reports the standard ( p ° = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, Δ f H m ∘ ( g ) , of 2,4-, 2,6-, and 3,5-dibromophenol, at T = 298.15 K, respectively, as (59.6 ± 2.6) kJ · mol −1 , (49.1 ± 2.2) kJ · mol −1 and (39.5 ± 2.0) kJ · mol −1 . These experimental values were derived from the measurements of the standard molar enthalpies of formation, in the crystalline phase, Δ f H m ∘ ( 2,4-dibromophenol,cr ) = - ( 140.9 ± 2.1 ) kJ · mol - 1 , Δ f H m ∘ ( 2,6-dibromophenol,cr ) = - ( 132.5 ± 1.6 ) kJ · mol - 1 and Δ f H m ∘ ( 3,5-dibromophenol,cr ) = - ( 134.5 ± 1.7 ) kJ · mol - 1 , at the same reference temperature, achieved from the standard molar enthalpies of combustion, in oxygen, to yield CO 2 (g) and HBr·600H 2 O(l), measured by rotating-bomb combustion calorimetry, together with measurements of the standard molar enthalpies of sublimation, at T = 298.15 K, as Δ cr g H m ∘ ( 2,4-dibromophenol ) = ( 81.3 ± 1.5 ) kJ · mol - 1 , Δ cr g H m ∘ ( 2,6-dibromophenol ) = ( 83.4 ± 1.5 ) kJ · mol - 1 and Δ cr g H m ∘ ( 3,5-dibromophenol ) = ( 94.3 ± 1.8 ) kJ · mol - 1 , obtained using the Calvet high temperature vacuum sublimation technique. The standard molar enthalpy of sublimation, at T = 298.15 K, for the 3,5-dibromophenol was also determined from the temperature–vapour pressure dependence, obtained by the Knudsen mass loss effusion method, Δ cr g H m ∘ ( 3,5-dibromophenol ) = ( 95.0 ± 1.1 ) kJ · mol - 1 . For this isomer it is also reported the standard ( p ° = 0.1 MPa) molar entropy and Gibbs energy of sublimation, at T = 298.15 K. The experimental values of the gas-phase enthalpies of formation of each compound were compared with estimates using the empirical scheme developed by Cox and with the calculated values based on density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional at the 6-311++G(d,p) basis set. These two methodologies were also used to estimate the enthalpies of formation in the gas-phase of the 2,3-, 2,5-, and 3,4-dibromophenol.

This work reports the experimental and computational thermochemical study performed on three difluorinated nitrobenzene isomers: 2,4-difluoronitrobenzene (2,4-DFNB), 2,5-difluoronitrobenzene (2,5-DFNB), and 3,4-difluoronitrobenzene (3,4-DFNB). The standard (p° = 0.1 MPa) molar enthalpies of formation in the liquid phase of these compounds were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by rotating bomb combustion calorimetry. A static method was used to perform the vapor pressure study of the referred compounds allowing the construction of the phase diagrams and determination of the respective triple point coordinates, as well as the standard molar enthalpies of vaporization, sublimation, and fusion for two of the isomers (2,4-DFNB and 3,4-DFNB). For 2,5-difluoronitrobenzene, only liquid vapor pressures were measured enabling the determination of the standard molar enthalpies of vaporization. Combining the thermodynamic parameters of the compounds studied, the following standard (p° = 0.1 MPa) molar enthalpies of formation in the gaseous phase, at T = 298.15 K, were derived: Δ(f)H(m)° (2,4-DFNB, g) = -(296.3 ± 1.8) kJ · mol⁻¹, Δ(f)H(m)° (2,5-DFNB, g) = -(288.2 ± 2.1) kJ · mol⁻¹, and Δ(f)H(m)° (3,4-DFNB, g) = -(302.4 ± 2.1) kJ · mol⁻¹. Using the empirical scheme developed by Cox, several approaches were evaluated in order to identify the best method for estimating the standard molar gas phase enthalpies of formation of these compounds. The estimated values were compared to the ones obtained experimentally, and the approach providing the best comparison with experiment was used to estimate the thermodynamic behavior of the other difluorinated nitrobenzene isomers not included in this study. Additionally, the enthalpies of formation of these compounds along with the enthalpies of formation of the other isomers not studied experimentally, i.e., 2,3-DFNB, 2,6-DFNB, and 3,5-DFNB, were estimated using the composite G3MP2B3 approach together with adequate gas-phase working reactions. Furthermore, we also used this computational approach to calculate the gas-phase basicities, proton and electron affinities, and, finally, adiabatic ionization enthalpies.

The standard ( p ∘ = 0.1 MPa ) molar enthalpies of formation of 2-chloro-4,6-dinitroaniline and 4-chloro-2,6-dinitroaniline, in the gaseous phase, at T = 298.15 K, were derived from the combination of the values of the standard molar enthalpies of formation, in the crystalline phase, and of the standard molar enthalpies of sublimation, at the same temperature. The standard molar enthalpies of formation, in the crystalline phase, were derived from the standard massic energies of combustion, in oxygen, measured by rotating-bomb combustion calorimetry. The standard molar enthalpies of sublimation were calculated, by the application of the Clausius–Clapeyron equation, to the vapour pressures at several temperatures, measured by Knudsen effusion technique. Compound - Δ f H m ∘ (cr) / ( kJ · mol - 1 ) Δ cr g H m ∘ / ( kJ · mol - 1 ) Δ f H m ∘ (g) / ( kJ · mol - 1 ) 2-Chloro-4,6-dinitroaniline 101.0 ± 1.9 115.0 ± 0.9 14.0 ± 2.1 4-Chloro-2,6-dinitroaniline 76.9 ± 1.8 105.2 ± 0.7 28.3 ± 1.9 The values of the standard molar enthalpies of formation of 2-chloro-4,6-dinitroaniline and 4-chloro-2,6-dinitroaniline, in the gaseous phase, at T = 298.15 K, are discussed in terms of enthalpic increments, and the enthalpy of isomerization between the two compounds is compared with the same parameter for two isomers of chloronitroaniline, studied in previous works.

The standard (p∘ = 0.1 MPa) molar enthalpies of formation, in the crystalline state, of 1,5-diaminonaphthalene and 1,8-diaminonaphthalene were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by static-bomb combustion calorimetry. The Knudsen mass-loss effusion technique was used to measure the dependence of the vapour pressure of the solid isomers of diaminonaphthalene with the temperature, from which the standard molar enthalpies of sublimation were derived using the Clausius–Clapeyron equation. - Δ c U m ∘ ( cr ) / ( kJ · mol - 1 ) Δ f H m ∘ ( cr ) / ( kJ · mol - 1 ) Δ cr g H m ∘ / ( kJ · mol - 1 ) 1,5-Diaminonaphthalene 5402.7 ± 2.2 42.1 ± 2.6 122.5 ± 0.9 1,8-Diaminonaphthalene 5425.9 ± 2.3 65.4 ± 2.6 99.0 ± 0.7 Combining these two experimental values, the gas-phase standard molar enthalpies of formation, at T = 298.15 K, were derived and compared with those estimated using two different empirical methods of Δ f H m ∘ ( g ) estimation: the Cox scheme and the Benson’s Group Method. Moreover, the standard (p∘ = 0.1 MPa) molar entropies and Gibbs energies of sublimation, at T = 298.15 K, were derived for the two diaminonaphthalene isomers.

The present work is part of a research program on the energetics of formation of alkyl substituted benzenediols, aiming the study of the enthalpic effect of the introduction of methyl substituents into benzenediols. In this work we present the results of the thermochemical research on 2-methylresorcinol, 3-methylresorcinol, 4-methylresorcinol, and methylhydroquinone. The standard ( p ∘ = 0.1 MPa ) molar enthalpies of formation, in the crystalline phase, at T = 298.15 K, of the compounds mentioned above were derived from their standard massic energies of combustion, measured by static-bomb combustion calorimetry, while the standard molar enthalpies of sublimation of those compounds were obtained by the temperature dependence of their vapour pressures determined by the Knudsen effusion technique. - Δ c U m ∘ ( cr ) / ( kJ · mol - 1 ) Δ f H m ∘ ( cr ) / ( kJ · mol - 1 ) Δ cr g H m ∘ / ( kJ · mol - 1 ) 2-Methylresorcinol (cr) 3499.3 ± 0.8 −393.6 ± 1.2 99.2 ± 2.3 4-Methylresorcinol (cr) 3491.3 ± 1.1 −401.6 ± 1.4 107.3 ± 3.0 5-Methylresorcinol (cr) 3491.4 ± 1.1 −401.5 ± 1.4 102.9 ± 3.5 Methylhydroquinone (cr) 3492.7 ± 1.4 −400.2 ± 1.7 108.4 ± 3.9 From those experimental values, the standard molar enthalpies of formation of the studied methylbenzenediols in the gaseous phase, at T = 298.15 K were then derived. The results are interpreted in terms of structural contributions to the energetics of the substituted benzenediols and compared with the same parameters estimated from the Cox Scheme. Moreover, the standard ( p ∘ = 0.1 MPa ) molar enthalpies, entropies, and Gibbs energies of sublimation, at T = 298.15 K, were derived for the four isomers of methylbenzenediols.

The standard (p° = 0.1 MPa) molar enthalpies of formation of 2,5- and 2,6-dichloro-4-nitroanilines, in the gaseous phase, at T = 298.15 K, were derived from the combination of the values of the standard molar enthalpies of formation in the crystalline phase, at T = 298.15 K, and the standard molar enthalpies of sublimation, of each compound, at the same temperature. The standard molar enthalpies of formation, in the crystalline phase, at T = 298.15 K, were derived from the standard massic energies of combustion of the two isomers, in oxygen, at T = 298.15 K, measured by rotating-bomb combustion calorimetry. The standard molar enthalpies of sublimation were calculated, by application of the Clausius–Clapeyron equation, to the vapour pressures at several temperatures measured by Knudsen effusion technique. Compound Δ f H m ∘ ( cr ) / ( kJ · mol - 1 ) Δ cr g H m ∘ / ( kJ · mol - 1 ) 2,5-Dichloro-4-nitroaniline −85.6 ± 1.9 114.3 ± 0.9 2,6-Dichloro-4-nitroaniline −107.3 ± 1.4 109.2 ± 0.9 The values of the standard (p = 0.1 MPa) molar enthalpies of formation of 2,5- and 2,6-dichloro-4-nitroanilines, in the gaseous phase, at T = 298.15 K, were compared with those estimated by the Cox scheme.

The standard ( p ∘ = 0.1 MPa ) molar enthalpies of formation of the liquid 2-bromophenol and crystalline 4-bromophenol, respectively, Δ f H m ∘ ( l ) = - ( 133.5 ± 1.4 ) kJ · mol - 1 and Δ f H m ∘ (cr) = - ( 152.4 ± 1.4 ) kJ · mol - 1 , were derived from the standard molar energies of combustion, in oxygen, to yield CO2(g) and HBr · 600H2O(l), at T = 298.15 K, measured by rotating-bomb combustion calorimetry. The Calvet high temperature vacuum sublimation technique was used to measure the enthalpy of vaporization or sublimation of the compounds, Δ 1 g H m ∘ = ( 55.5 ± 1.3 ) kJ · mol - 1 and Δ cr g H m ∘ = ( 83.1 ± 1.6 ) kJ · mol - 1 . These two thermodynamic parameters yielded the standard molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, of 2- and 4-bromophenol, respectively, Δ f H m ∘ ( g ) = - ( 78.0 ± 1.9 ) kJ · mol - 1 and Δ f H m ∘ ( g ) = - ( 69.3 ± 2.1 ) kJ · mol - 1 . The experimental values of the gas-phase enthalpies of formation of each compound were compared with estimates using the empirical scheme developed by Cox and with the calculated values based on high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional at the 6-311++G(d,p) basis set.

The standard ( p ∘ = 0.1 MPa ) molar enthalpies of formation of 2,4,6-trichloronitrobenzene, 2,3,5,6-tetrachloronitrobenzene, and pentachloronitrobenzene, in the crystalline state, at T = 298.15 K, were derived from the standard massic energies of combustion, in oxygen, at T = 298.15 K, measured by rotating-bomb combustion calorimetry. The standard molar enthalpies of sublimation, at T = 298.15 K, of 2,4,6-trichloronitrobenzene and pentachloronitrobenzene, were determined from the dependence with the temperature of the vapour pressures, measured by the Knudsen mass-loss effusion method, whereas for 2,3,5,6-tetrachloronitrobenzene, the Calvet drop microcalorimetric technique was used. - Δ c U m ∘ ( cr ) /(kJ · mol−1) - Δ f H m ∘ ( cr ) /(kJ · mol−1) Δ cr g H m ∘ /(kJ · mol−1) 2,4,6-Trichloronitrobenzene 2663.5 ± 1.1 58.6 ± 1.3 86.7 ± 1.1 2,3,5,6-Tetrachloronitrobenzene 2537.1 ± 1.7 67.0 ± 1.9 91.3 ± 2.5 Pentachloronitrobenzene 2387.4 ± 2.4 98.6 ± 2.5 94.5 ± 0.4 The experimental values are also compared with estimates based on G3(MP2)//B3LYP computations, which have also been extended to all the isomers of the trichloro- and tetrachloronitrobenzene that were not studied experimentally.

The standard (p° = 0.1 MPa) molar enthalpies of formation of 2,4-, 2,5-, 3,4- and 3,5-dichloronitrobenzene isomers, in the crystalline state, at T = 298.15 K, were derived from the standard (p° = 0.1 MPa) massic energies of combustion, in oxygen, at T = 298.15 K, measured by rotating bomb combustion calorimetry. The standard molar enthalpies of sublimation of the four isomers, at T = 298.15 K, were obtained by high-temperature Calvet microcalorimetry. - Δ c U m ∘ ( cr ) / ( kJ · mol - 1 ) - Δ f H m ∘ (cr) / ( kJ · mol - 1 ) Δ cr g H m ∘ / ( kJ · mol - 1 ) 2,4-Dichloronitrobenzene 2792.8 ± 0.9 47.4 ± 1.2 87.8 ± 1.7 2,5-Dichloronitrobenzene 2793.0 ± 1.8 47.2 ± 2.0 87.4 ± 2.5 3,4-Dichloronitrobenzene 2774.1 ± 1.2 66.1 ± 1.4 85.8 ± 2.5 3,5-Dichloronitrobenzene 2769.6 ± 0.9 70.6 ± 1.2 83.2 ± 1.5 From the determined experimental results, the values of the gaseous standard (p° = 0.1 MPa) molar enthalpies of formation were derived. The gas-phase enthalpies of formation of all the six chloronitrobenzene isomers were also estimated by the Cox scheme and by computational thermochemistry methods and compared with the available experimental values.

The present work reports the values of the standard (po = 0.1 MPa) molar enthalpies of formation in the condensed phase of the three isomers of monofluorophenol derived from the standard molar energies of combustion, in oxygen, to yield CO2(g) and HF·10H2O(l), at T = 298.15 K, measured by rotating bomb combustion calorimetry, as well as the values of the standard molar enthalpies of sublimation or vaporization, at T = 298.15 K, determined using high temperature Calvet microcalorimetry. Combining the former two experimental quantities, the standard molar enthalpies of formation in the gaseous phase were derived, at T = 298.15 K: ΔfHmo(2-fluorophenol, g) = −(294.5 ± 1.6) kJ·mol−1, ΔfHmo(3-fluorophenol, g) = −(292.8 ± 1.7) kJ·mol−1, and ΔfHmo(4-fluorophenol, g) = −(287.6 ± 2.1) kJ·mol−1. The experimental values of the gas-phase enthalpies of formation of each compound were compared with estimates using the empirical scheme developed by Cox and with the calculated values based on high-level density functional...

The standard ( p ° = 0.1 MPa) molar enthalpies of formation in the liquid phase of three isomers of bromoanisole were derived from the standard molar energies of combustion, in oxygen, which yields CO 2 (g) and HBr · 600H 2 O(l), at T = 298.15 K, measured by rotating bomb combustion calorimetry. The determination of the standard molar enthalpies of vaporization of these compounds, at T = 298.15 K, was done by Calvet microcalorimetry using the high-temperature vacuum sublimation technique. Combining the former sets of experimental results, the standard molar enthalpies of formation, in the gas-phase, were derived. The gas-phase enthalpies of formation were also estimated by means of the empirical scheme developed by Cox and by density functional theory calculations performed at the B3LYP/6-31+G(d) level of theory. - Δ c U m ∘ ( l ) / ( kJ · mol - 1 ) - Δ f H m ∘ ( l ) / ( kJ · mol - 1 ) Δ l g H m ∘ / ( kJ · mol - 1 ) 2-Bromoanisole 3629.0 ± 1.4 101.5 ± 1.7 61.8 ± 1.3 3-Bromoanisole 3624.0 ± 1.4 106.5 ± 1.7 58.0 ± 1.2 4-Bromoanisole 3623.8 ± 1.5 106.7 ± 1.8 58.3 ± 1.2 Full-size table Table options View in workspace Download as CSV

The standard (p∘ = 0.1 MPa) molar enthalpies of formation in the liquid phase of three isomers of fluoroanisole were derived from the standard molar energies of combustion, in oxygen, to yield CO2(g) and HF · 10H2O(l), at T = 298.15 K, measured by rotating bomb combustion calorimetry. The standard molar enthalpies of vaporization of these compounds, also at T = 298.15 K, were determined using Calvet microcalorimetry. - Δ c U m ∘ ( l ) / ( kJ · mol - 1 ) - Δ f H m ∘ ( l ) / ( kJ · mol - 1 ) Δ l g H m ∘ / ( kJ · mol - 1 ) 2-Fluoroanisole 3629.7 ± 1.0 301.9 ± 1.5 52.2 ± 1.1 3- Fluoroanisole 3617.1 ± 1.1 314.5 ± 1.6 48.1 ± 1.1 4- Fluoroanisole 3622.4 ± 1.2 309.2 ± 1.6 48.7 ± 1.1 The standard molar enthalpies of formation in the gaseous phase, at T = 298.15 K, were derived from the former two experimental quantities. These values are also compared with estimates based on two different methodologies: one using the empirical scheme developed by Cox and the other one based on high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional at the 6-311++G(d,p) basis set. The computed values and the estimated values using the Cox method compare well with the experimental results obtained in this work.

The standard (p∘ = 0.1 MPa) molar enthalpies of formation of 2-, 3-, and 4-chloronitrobenzene isomers, in the crystalline state, at T = 298.15 K, were derived from the standard (p∘ = 0.1 MPa) massic energies of combustion, in oxygen, at T = 298.15 K, measured by rotating bomb combustion calorimetry. The standard molar enthalpies of sublimation of the isomers, at T = 298.15 K, were obtained by high temperature Calvet microcalorimetry. - Δ c U m ∘ ( cr ) /(kJ · mol−1) - Δ c H m ∘ ( cr ) /(kJ · mol−1) - Δ cr g H m ∘ /(kJ · mol−1) 2-Chloronitrobenzene 2939.5 ± 0.7 18.7 ± 1.0 80.9 ± 1.5 3-Chloronitrobenzene 2915.8 ± 0.8 42.4 ± 1.2 82.5 ± 1.5 4-Chloronitrobenzene 2921.7 ± 1.4 36.5 ± 1.6 76.2 ± 2.1 From the determined experimental data, the values of the gaseous standard (p∘ = 0.1 MPa) molar enthalpies of formation for the three monochloronitrobenzene isomers were derived. The gas-phase enthalpies of formation were also estimated by the empirical scheme developed by Cox showing that for meta- and para-chloronitrobenzene the estimated values are in close agreement with the experimental ones whereas, in the case of ortho-chloronitrobenzene it is shown that a different enthalpic interaction increment is needed, when the substituents in the adjacent carbon ring atoms are a chlorine atom and a nitro group.

The present work reports the values of the gaseous standard ( p ∘ = 0.1 MPa) molar enthalpies of formation of four isomers of dichloroanisole: 2,3-, 2,4-, 2,6-, and 3,5-dichloroanisole, at T = 298.15 K. For all compounds, those values were derived from measurements of the standard molar energies of combustion in the condensed phase, using a rotating bomb combustion calorimeter, together with measurements of the standard molar enthalpies of sublimation or vaporization, measured by high temperature Calvet microcalorimetry. Moreover, the enthalpies and the temperatures of fusion for the crystalline isomers of dichloroanisoles were measured by differential scanning calorimetry. - Δ c U m ∘ ( cr, l ) / ( kJ · mol - 1 ) - Δ f H m ∘ ( cr, l ) / ( kJ · mol - 1 ) Δ cr, l g H m ∘ / ( kJ · mol - 1 ) 2,3-Dichloroanisole (cr) 3456.8 ± 1.5 201.3 ± 1.8 83.6 ± 1.5 2,4-Dichloroanisole (l) 3473.7 ± 1.4 184.4 ± 1.7 62.8 ± 0.7 2,6-Dichloroanisole (l) 3492.7 ± 1.5 165.4 ± 1.8 56.1 ± 0.7 3,5-Dichloroanisole (cr) 3453.2 ± 1.5 204.9 ± 1.8 79.0 ± 1.5 The derived standard molar enthalpies of formation in the gaseous phase, at T = 298.15 K, for the title compounds were compared with the same parameters estimated by the Cox scheme and interpreted in terms of molecular structure.

The standard (p∘ = 0.1 MPa) molar enthalpies of formation, in the liquid phase, of 2-, 3- and 4-chloroanisoles, at T = 298.15 K, were derived from their standard massic energies of combustion, in oxygen, to yield CO2(g) and HCl · 600H2O(l), measured by rotating bomb combustion calorimetry. The Calvet high-temperature microcalorimetry technique was used to measure the standard molar enthalpies of vaporization of these compounds. - Δ c U m ∘ ( l ) / ( kJ · mol - 1 ) - Δ f H m ∘ ( l ) / ( kJ · mol - 1 ) Δ l g H m ∘ / ( kJ · mol - 1 ) 2-Chloroanisole 3622.0 ± 1.6 154.1 ± 1.8 55.0 ± 0.8 3-Chloroanisole 3615.9 ± 1.6 160.2 ± 1.8 53.6 ± 0.8 4-Chloroanisole 3619.2 ± 1.5 156.9 ± 1.8 54.8 ± 0.8 From these two sets of experimental values, the standard molar enthalpies of formation in the gaseous phase, at T = 298.15 K, were derived, compared with the same parameters estimated by the Cox scheme and interpreted in terms of molecular structure.

The standard (p∘ = 0.1 MPa) molar enthalpies of formation in the crystalline state of phenylacetic acid and ortho-, meta- and para-chlorophenylacetic acids were derived from the standard molar energies of combustion in oxygen at T = 298.15 K, measured by combustion calorimetry. The Knudsen mass-loss effusion technique was used to measure the dependence of the vapour pressure of the solid isomers of chlorophenylacetic acid with the temperature from which the standard molar enthalpies of sublimation were derived using the Clausius–Clapeyron equation. - Δ c U m ∘ ( cr ) kJ · mol - 1 - Δ f H m ∘ ( cr ) kJ · mol - 1 Δ cr g H m ∘ kJ · mol - 1 Phenylacetic acid 3887.6 ± 1.6 401.3 ± 1.9 99.0 ± 0.6 2-Chlorophenylacetic acid 3722.7 ± 1.1 448.2 ± 1.5 110.9 ± 0.5 3-Chlorophenylacetic acid 3725.2 ± 1.1 445.7 ± 1.5 109.5 ± 0.6 4-Chlorophenylacetic acid 3727.8 ± 1.0 443.1 ± 1.4 109.7 ± 0.6 From these values the standard molar enthalpies in the gaseous phase, at T = 298.15 K, were derived, compared with the same parameters estimated from the Cox scheme and interpreted in terms of molecular structure. The standard (p∘ = 0.1 MPa) molar enthalpies, entropies, and Gibbs energies of sublimation, at T = 298.15 K, were derived for the three monochlorophenylacetic acids, using estimated values for the heat capacity differences between the gas and the crystal phases. Moreover, the enthalpies and the temperatures of fusion for the crystalline isomers of chlorophenylacetic acid were measured by differential scanning calorimetry.

The gas-phase standard molar enthalpies of formation of the three monoiodoanilines were derived from the enthalpies of combustion in the condensed phases, measured by rotating-bomb calorimetry and their enthalpies of sublimation/vaporization obtained by Calvet microcalorimetry at T = 298.15 K. The standard enthalpies of formation for these compounds and for the diiodoaniline isomers were determined by DFT calculations. The theoretical calculations were performed with the B3LYP/6-31G(d):SBKJ-VDZ and B3LYP/6-311G(2d, 2p):SBKJ-VDZ approaches. Estimated values are in excellent agreement with the reported experimental numbers derived in the present Letter.

The standard (p degrees = 0.1 MPa) molar enthalpies of formation of 2-, 3-, and 4-chloroaniline were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by rotating bomb combustion calorimetry. The Calvet high-temperature vacuum sublimation technique was used to measure the enthalpies of vaporization or sublimation of the three isomers. These two thermodynamic parameters yielded the standard molar enthalpies of formation of the three isomers of chloroaniline, in the gaseous phase, at T = 298.15 K, as 53.4 +/- 3.1 kJ.mol(-1) for 2-chloroaniline, 53.0 +/- 2.8 kJ.mol(-1) for 3-chloroaniline, and 59.7 +/- 2.3 kJ.mol(-1) for 4-chloroaniline. These values, which correct previously published data, were used to test the computational methodologies used. Therewith, gas-phase acidities, proton affinities, electron donor capacities, and N-H bond dissociation enthalpies were calculated and found to compare well with available experimental data for these parameters.

The standard (po=0.1 MPa) molar enthalpies of formation for crystalline 2-chloro-4-nitroaniline and 2-chloro-5-nitroaniline were derived from the standard molar enthalpies of combustion, in oxygen, at the T=298.15 K, measured by rotating bomb combustion calorimetry. The Knudsen mass-loss effusion technique was used to measure the vapour pressures of the crystals as function of temperature, and the standard molar enthalpies of sublimation, at T=298.15 K, were derived by the Clausius–Clapeyron equation. Direct measurements of the standard molar enthalpies of sublimation, using Calvet microcalorimetry, for 2-chloro-4-nitroaniline and 2-chloro-5-nitroaniline confirmed the values derived from the Knudsen technique. Δ f H m 0 (cr) Δ cr g H m 0 (kJ · mol−1) (kJ · mol−1) Calvet Knudsen 2-Chloro-4-nitroaniline (2-Cl-4-NO2-C6H3NH2) −74.9 ± 1.4 101.8 ± 1.8 102.6 ± 1.5 2-Chloro-5-nitroaniline (2-Cl-5-NO2-C6H3NH2) −71.0 ± 1.5 100.3 ± 2.2 101.0 ± 1.6 Additionally, standard enthalpies of formation were estimated by employing two different methodologies. One is based on the Cox scheme and the other one, much more accurate, is based on first-principles calculations. The theoretical calculations were performed at the AM1, B3LYP/6-31+G** and BP86/6-31+G** levels of theory. Estimated values are in good agreement with the reported experimental numbers.

The standard ( p o = 0.1 MPa) molar enthalpies of formation Δ f H m o , at the temperature 298.15 K, for crystalline 2,3,4-, 2,4,5-, 2,4,6- and 3,4,5-trichloroaniline were derived from the molar enthalpies of combustion Δ c H m o in oxygen using rotating bomb combustion calorimetry. The reaction products were CO 2 (g) , N 2 (g) , and HCl · 600H 2 O(l) . The standard molar enthalpies of sublimation Δ cr g H m o at T = 298.15 K were measured by Calvet microcalorimetry. The results are as follows: The derived standard molar enthalpies of formation of the gaseous compounds were compared with values estimated by assuming the enthalpy increment for substitution of chlorine in aniline to be the same as for substitution into benzene.

The standard (p° = 0.1 MPa) molar enthalpies of formation, of the 2-, 3-, and 4-monobromonitrobenzene isomers, in the crystalline phase, at T = 298.15 K, were derived from the standard massic energies of combustion, in oxygen, at T = 298.15 K, 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 using the Clausius-Clapeyron equation. - Δ c U m ∘ ( cr ) / ( kJ · mol - 1 ) Δ f H m ∘ ( cr ) / ( kJ · mol - 1 ) Δ cr g H m ∘ / ( kJ · mol - 1 ) 2-Bromonitrobenzene 2939.5 ± 1.0 26.9 ± 1.3 85.2 ± 0.3 3-Bromonitrobenzene 2919.7 ± 1.1 7.1 ± 1.3 86.8 ± 0.5 4-Bromonitrobenzene 2913.1 ± 0.9 0.5 ± 1.2 86.6 ± 0.6 The combination of the values of the standard molar enthalpies of formation in the crystalline phase, and of the standard molar enthalpies of sublimation, yielded the standard molar enthalpies of formation in the gaseous phase. The results were interpreted in terms of enthalpic increments, and compared with estimated values applying the empirical scheme developed by Cox.

The present work reports the thermodynamic study performed on three monofluorinated nitrobenzene derivatives by a combination of experimental techniques and computational approaches. The standard (p degrees = 0.1 MPa) molar enthalpies of formation in the liquid phase of the three isomers of fluoronitrobenzene were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by rotating bomb combustion calorimetry. The vapor pressure study of the referred compounds was done by a static method and, from the obtained results, the phase diagrams were elaborated, and the respective triple point coordinates, as well as the standard molar enthalpies of vaporization, sublimation and fusion, at T = 298.15 K, were determined. The combination of some of the referred thermodynamic parameters yielded the standard (p degrees = 0.1 MPa) molar enthalpies of formation in the gaseous phase, at T = 298.15 K, of the studied compounds: Delta(f)H(m)degrees(2-fluoronitrobenzene, g) = -(102.4 +/- 1.5) kJ.mol(-1), Delta(f)H(m)degrees(3-fluoronitrobenzene, g) = -(128.0 +/- 1.7) kJ.mol(-1), and Delta(f)H(m)degrees(4-fluoronitrobenzene, g) = -(133.9 +/- 1.4) kJ.mol(-1). Using the empirical scheme developed by Cox, values of standard molar enthalpies of formation in the gaseous phase were estimated and afterwards compared with the ones obtained experimentally, and both were interpreted in terms of the molecular structure of the compounds. 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. The computed values compare very well with the experimental results obtained in this work and show that 4-fluoronitrobenzene is the most stable isomer from the thermodynamic point of view. Furthermore, this composite approach was also used to obtain information about the gas-phase basicities, proton and electron affinities and, finally, adiabatic ionization enthalpies.

The present work is part of a research program on the energetics of the linear 4-n-alkoxybenzoic acids, aiming the study of the enthalpic effect of the introduction of an alkoxy chain in the position 4- of the benzoic acid ring. In this work, we present the results of the thermochemical research on 4-n-alkoxybenzoic acids with the alkoxy chain length n = 2, 4, and 8. The standard ( p ∘ = 0.1 MPa ) molar enthalpy of formation of crystalline 4-ethoxybenzoic acid, 4-butoxybenzoic acid, and 4-(octyloxy)benzoic acid was measured, at T = 298.15 K, by static-bomb calorimetry. These values, combined with the values of standard molar enthalpies of sublimation, were used to derive the standard molar enthalpies of formation in the gaseous phase. 4-Alkoxybenzoic acid - Δ c U m ∘ ( cr ) / ( kJ · mol - 1 ) - Δ f H m ∘ (cr ) / ( kJ · mol - 1 ) - Δ f H m ∘ ( g ) / ( kJ · mol - 1 ) 4-Ethoxybenzoic acid 4362.7 ± 1.3 605.5 ± 1.8 482.2 ± 2.0 4-Butoxybenzoic acid 5677.3 ± 2.0 647.1 ± 2.5 518.1 ± 2.6 4-(Octyloxy)benzoic acid 8269.0 ± 3.3 767.9 ± 3.9 604.9 ± 4.1 From those experimental values, the standard molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, are interpreted in terms of structural contributions to the energetics of the substituted benzoic acids and compared with the same parameters estimated from the Benson’s Group Method.

The energetics of the C-F, C-Cl, C-Br, and C-I bonds in 2-haloethanols was investigated by using a combination of experimental and theoretical methods. The standard molar enthalpies of formation of 2-chloro-, 2-bromo-, and 2-iodoethanol, at 298.15 K, were determined as Delta(f)H(degree)m(CH2CH2OH, l) = -315.5 +/- 0.7 kJ.mol-1, Delta(f)H(degree)mBrCH2CH2OH, l) = -275.8 +/- 0.6 kJ.mol-1, Delta(f)H(degree)m(ICH2CH2OH, l) = -207.3 +/- 0.7 kJ.mol-1, by rotating-bomb combustion calorimetry. The corresponding standard molar enthalpies of vaporization, Delta(vap)H(degree)m(ClCH2CH2OH) = 48.32 +/- 0.37 kJ.mol-1, Delta(vap)H(degree)m(BrCH2CH2OH) = 54.08 +/- 0.40 kJ.mol-1, and Delta(vap)H(degree)m(ICH2CH2OH) = 57.03 +/- 0.20 kJ.mol-1 were also obtained by Calvet-drop microcalorimetry. The condensed phase and vaporization enthalpy data lead to Delta(f)H(degree)m(ClCH2CH2OH, g) = -267.2 +/- 0.8 kJ.mol-1, Delta(f)H(degree)m(BrCH2CH2OH, g) = -221.7 +/- 0.7 kJ.mol-1, and Delta(f)H(degree)m(ICH2CH2OH, g) = -150.3 +/- 0.7 kJ.mol-1. These values, together with the enthalpy of selected isodesmic and isogyric gas-phase reactions predicted by density functional theory (B3LYP/cc-pVTZ) and CBS-QB3 calculations were used to derive the enthalpies of formation of gaseous 2-fluoroethanol, Delta(f)H(degree)m(FCH2CH2OH, g) = -423.6 +/- 5.0 kJ.mol-1, and of the 2-hydroxyethyl radical, Delta(f)H(degree)m(CH2CH2OH, g) = -28.7 +/- 8.0 kJ.mol-1. The obtained thermochemical data led to the following carbon-halogen bond dissociation enthalpies: DHo(X-CH2CH2OH) = 474.4 +/- 9.4 kJ.mol-1 (X = F), 359.9 +/- 8.0 kJ.mol-1 (X = Cl), 305.0 +/- 8.0 kJ.mol-1 (X = Br), 228.7 +/- 8.1 kJ.mol-1 (X = I). These values were compared with the corresponding C-X bond dissociation enthalpies in XCH2COOH, XCH3, XC2H5, XCH=CH2, and XC6H5. In view of this comparison the computational methods mentioned above were also used to obtain Delta(f)H(degree)m-594.0 +/- 5.0 kJ.mol-1 from which DHo(F-CH2COOH) = 435.4 +/- 5.4 kJ.mol-1. The order DHo(C-F)DHo(C-Cl)DHo(C-Br)DHo(C-I) is observed for the haloalcohols and all other RX compounds. It is finally concluded that the major qualitative trends exhibited by the C-X bond dissociation enthalpies for the series of compounds studied in this work can be predicted by Pauling's electrostatic-covalent model.