Study on the thermodynamic properties of cholesterol

The standard molar enthalpy of combustion of cholesterol was measured at constant volume. According to value of Δ_r U _m^θ(−14358.4±20.65 kJ mol⁻¹), Δ_r H _m^θ(−14385.7 kJ mol⁻¹) of combustion reaction and Δ_f H _m^θ(2812.9 kJ mol⁻¹) of cholesterol were obtained from the reaction equation. The enthalpy of combustion reaction of cholesterol was also estimated by the average bond enthalpies. By design of a thermo-chemical recycle, the enthalpy of combustion of cholesterol were calculated between 283.15∼373.15 K. Besides, molar enthalpy and entropy of fusion of cholesterol was obtained by DSC technique.     

Thermochemical studies on the thioproline

The combustion energy of thioproline was determined by the precision rotating-bomb calorimeter at 298.15 K to be Δ_c U= –2469.30±1.44 kJ mol^–1. From the results and other auxiliary quantities, the standard molar enthalpy of combustion and the standard molar enthalpy of formation of thioproline were calculated to be Δ_c H _m ^θC₄H₇NO₂S, (s), 298.15 K= –2469.92±1.44 kJ mol^–1 and Δ_f H _m ^θC₄H₇NO₂S, (s), 298.15K= –401.33±1.54 kJ mol^–1.     

Molar heat capacities and standard molar enthalpy of formation of 2-amino-5-methylpyridine

The heat capacities (C _p,m) of 2-amino-5-methylpyridine (AMP) were measured by a precision automated adiabatic calorimeter over the temperature range from 80 to 398 K. A solid-liquid phase transition was found in the range from 336 to 351 K with the peak heat capacity at 350.426 K. The melting temperature (T _m), the molar enthalpy (Δ_fus H _m⁰), and the molar entropy (Δ_fus S _m⁰) of fusion were determined to be 350.431±0.018 K, 18.108 kJ mol⁻¹ and 51.676 J K⁻¹ mol⁻¹, respectively. The mole fraction purity of the sample used was determined to be 0.99734 through the Van’t Hoff equation. The thermodynamic functions (H _T-H _298.15 and S _T-S _298.15) were calculated. The molar energy of combustion and the standard molar enthalpy of combustion were determined, ΔU _c(C₆H₈N₂,cr)= −3500.15±1.51 kJ mol⁻¹ and Δ_c H _m⁰ (C₆H₈N₂,cr)= −3502.64±1.51 kJ mol⁻¹, by means of a precision oxygen-bomb combustion calorimeter at T=298.15 K. The standard molar enthalpy of formation of the crystalline compound was derived, Δ_r H _m⁰ (C₆H₈N₂,cr)= −1.74±0.57 kJ mol⁻¹.     

Thermochemical study of the solid complex Ho(PDC)3 (o-phen)

A novel solid complex, formulated as Ho(PDC)₃ (o-phen), has been obtained from the reaction of hydrate holmium chloride, ammonium pyrrolidinedithiocarbamate (APDC) and 1,10-phenanthroline (o-phen·H₂O) in absolute ethanol, which was characterized by elemental analysis, TG-DTG and IR spectrum. The enthalpy change of the reaction of complex formation from a solution of the reagents, Δ_rH_m^θ (sol), and the molar heat capacity of the complex, c_m, were determined as being –19.161±0.051 kJ mol^–1 and 79.264±1.218 J mol^–1 K^–1 at 298.15 K by using an RD-496 III heat conduction microcalorimeter. The enthalpy change of complex formation from the reaction of the reagents in the solid phase, Δ_rH_m^θ(s), was calculated as being (23.981±0.339) kJ mol^–1 on the basis of an appropriate thermochemical cycle and other auxiliary thermodynamic data. The thermodynamics of reaction of formation of the complex was investigated by the reaction in solution at the temperature range of 292.15–301.15 K. The constant-volume combustion energy of the complex, Δ_cU, was determined as being –16788.46±7.74 kJ mol^–1 by an RBC-II type rotating-bomb calorimeter at 298.15 K. Its standard enthalpy of combustion, Δ_cH_m^θ, and standard enthalpy of formation, Δ_fH_m^θ, were calculated to be –16803.95±7.74 and –1115.42±8.94 kJ mol^–1, respectively.     

Thermochemistry of europium and dithiocarbamate complex Eu(C5H8NS2)3(C12H8N2)

A solid complex Eu(C₅H₈NS₂)₃(C₁₂H₈N₂) has been obtained from reaction of hydrous europium chloride with ammonium pyrrolidinedithiocarbamate (APDC) and 1,10-phenanthroline (o-phen⋅H₂O) in absolute ethanol. IR spectrum of the complex indicated that Eu³⁺ in the complex coordinated with sulfur atoms from the APDC and nitrogen atoms from the o-phen. TG-DTG investigation provided the evidence that the title complex was decomposed into EuS. The enthalpy change of the reaction of formation of the complex in ethanol, Δ_r H _m ^θ(l), as –22.214±0.081 kJ mol^–1, and the molar heat capacity of the complex, c _m, as 61.676±0.651 J mol^–1 K^–1, at 298.15 K were determined by an RD-496 III type microcalorimeter. The enthalpy change of the reaction of formation of the complex in solid, Δ_r H _m ^θ(s), was calculated as 54.527±0.314 kJ mol^–1 through a thermochemistry cycle. Based on the thermodynamics and kinetics on the reaction of formation of the complex in ethanol at different temperatures, fundamental parameters, including the activation enthalpy (ΔH _≠ ^θ), the activation entropy (ΔS _≠ ^θ), the activation free energy (ΔG _≠ ^θ), the apparent reaction rate constant (k), the apparent activation energy (E), the pre-exponential constant (A) and the reaction order (n), were obtained. The constant-volume combustion energy of the complex, Δ_c U, was determined as –16937.88±9.79 kJ mol^–1 by an RBC-II type rotating-bomb calorimeter at 298.15 K. Its standard enthalpy of combustion, Δ_c H _m ^θ, and standard enthalpy of formation, Δ_f H _m ^θ, were calculated to be –16953.37±9.79 and –1708.23±10.69 kJ mol^–1, respectively.     

Constant-volume combustion energy of the lead salts of 2HDNPPb and 4HDNPPb and their effect on combustion characteristics of RDX–CMDB propellant

The constant-volume combustion energies of the lead salts of 2-hydroxy-3,5-dinitropyridine (2HDNPPb) and 4-hydroxy-3,5-dinitropyridine (4HDNPPb), ΔU _c (2HDNPPb(s) and 4HDNPP(s)), were determined as –4441.92±2.43 and –4515.74±1.92 kJ mol^–1 , respectively, at 298.15 K. Their standard enthalpies of combustion, Δ_c ^m H θ(2HDNPPb(s) and 4HDNPPb(s), 298.15 K), and standard enthalpies of formation, Δ_r ^m H θ(2HDNPPb(s) and 4HDNPPb(s), 298.15 K) were as –4425.81±2.43, –4499.63±1.92 kJ mol^–1 and –870.43±2.76, –796.65±2.32 kJ mol^–1 , respectively. As two combustion catalysts, 2HDNPPb and 4HDNPPb can enhance the burning rate and reduce the pressure exponent of RDX–CMDB propellant.     

Thermodynamic investigation of several natural polyols

The low-temperature heat capacity C _p,m of erythritol (C₄H₁₀O₄, CAS 149-32-6) was precisely measured in the temperature range from 80 to 410 K by means of a small sample automated adiabatic calorimeter. A solid-liquid phase transition was found at T=390.254 K from the experimental C _p-T curve. The molar enthalpy and entropy of this transition were determined to be 37.92±0.19 kJ mol⁻¹ and 97.17±0.49 J K⁻¹ mol⁻¹, respectively. The thermodynamic functions [H _T-H _298.15] and [S _T-S _298.15], were derived from the heat capacity data in the temperature range of 80 to 410 K with an interval of 5 K. The standard molar enthalpy of combustion and the standard molar enthalpy of formation of the compound have been determined: Δ_c H _m⁰(C₄H₁₀O₄, cr)= −2102.90±1.56 kJ mol⁻¹ and Δ_f H _m⁰(C₄H₁₀O₄, cr)= − 900.29±0.84 kJ mol⁻¹, by means of a precision oxygen-bomb combustion calorimeter at T=298.15 K. DSC and TG measurements were performed to study the thermostability of the compound. The results were in agreement with those obtained from heat capacity measurements.     

The standard enthalpy of formation of silver pivalate

The standard enthalpy of combustion of crystalline silver pivalate, (CH₃)₃CC(O)OAg (AgPiv), was determined in an isoperibolic calorimeter with a self-sealing steel bomb, Δ_c H ⁰ (AgPiv, cr)= −2786.9±5.6 kJ mol⁻¹. The value of standard enthalpy of formation was derived for crystalline state: Δ_f H ⁰(AgPiv,cr)= −466.9±5.6 kJ mol⁻¹. Using the enthalpy of sublimation, measured earlier, the enthalpy of formation of gaseous dimer was obtained: Δ_f H ⁰(Ag₂Piv₂,g)= −787±14 kJ mol⁻¹. The enthalpy of reaction (CH₃)₃CC(O)OAg(cr)=Ag(cr)+(CH₃)₃CC(O)O^.(g) was estimated, Δ_r H ⁰=202 kJ mol⁻¹.     

Standard enthalpy of formation of 3,4,5-trimethoxybenzoic acid

The energy of combustion of crystalline 3,4,5-trimethoxybenzoic acid in oxygen at T=298.15 K was determined to be -4795.9±1.3 kJ mol^-1 using combustion calorimetry. The derived standard molar enthalpies of formation of 3,4,5-trimethoxybenzoic acid in crystalline and gaseous states at T=298.15 K, Δ_fH_m ^Θ (cr) and Δ_fH_m ^Θ (g), were -852.9±1.9 and -721.7±2.0 kJ mol^-1, respectively. The reliability of the results obtained was commented upon and compared with literature values. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermochemistry of the ternary solid complex Gd(C5H8NS2)3(C12H8N2)

The novel ternary solid complex Gd(C₅H₈NS₂)₃(C₁₂H₈N₂) has been obtained from the reaction of hydrous gadolinium chloride, ammonium pyrrolidinedithiocarbamate (APDC), and 1,10-phenanthroline (o-phen · H₂O) in absolute ethanol. The complex was described by an elemental analysis, TG-DTG, and an IR spectrum. The enthalpy change of the complex formation reaction from a solution of the reagents, Δ_r H _m ^ϑ (sol), and the molar heat capacity of the complex, c _m , were determined as being − 15.174 ± 0.053 kJ/mol and 72.377 ± 0.636 J/(mol K) at 298.15 K by using an RD496-III heat conduction microcalorimeter. The enthalpy change of a complex formation from the reaction of the reagents in a solid phase, Δ_r H _m ^ϑ (s), was calculated as being 52.703 ± 0.304 kJ/mol on the basis of an appropriate thermochemical cycle and other auxiliary thermodynamic data. The thermodynamics of the formation reaction of the complex was investigated by the reaction in solution. Fundamental parameters, the activation enthalpy (ΔH _≠ ^ϑ ), the activation entropy (ΔS _≠ ^ϑ ), the activation free energy (ΔG _≠ ^ϑ ), the apparent reaction rate constant (k), the apparent activation energy (E), the preexponential constant (A), and the reaction order (n), were obtained by the combination of the thermochemical data of the reaction and kinetic equations, with the data of thermokinetic experiments. The constant-volume combustion energy of the complex, Δ_c U, was determined as being −17588.79 ± 8.62 kJ/mol by an RBC-II type rotatingbomb calorimeter at 298.15 K. Its standard enthalpy of combustion, Δ_c H _m ^ϑ , and standard enthalpy of formation, Δ_f H _m ^ϑ , were calculated to be −17604.28 ± 8.62 and −282.43 ± 9.58 kJ/mol, respectively. The text was submitted by the authors in English.     

Thermodynamic investigation of room temperature ionic liquid

The molar heat capacities of the room temperature ionic liquid 1-butylpyridinium tetrafluoroborate (BPBF₄) were measured by an adiabatic calorimeter in temperature range from 80 to 390 K. The dependence of the molar heat capacity on temperature is given as a function of the reduced temperature X by polynomial equations, C _p,m [J K⁻¹ mol⁻¹]=181.43+51.297X −4.7816X ²−1.9734X ³+8.1048X ⁴+11.108X ⁵ [X=(T−135)/55] for the solid phase (80–190 K), C _p,m [J K⁻¹ mol⁻¹]= 349.96+25.106X+9.1320X ²+19.368X ³+2.23X ⁴−8.8201X ⁵ [X=(T−225)/27] for the glass state (198–252 K), and C _p,m[J K⁻¹ mol⁻¹]= 402.40+21.982X−3.0304X ²+3.6514X ³+3.4585X ⁴ [X=(T−338)/52] for the liquid phase (286–390 K), respectively. According to the polynomial equations and thermodynamic relationship, the values of thermodynamic function of the BPBF₄ relative to 298.15 K were calculated in temperature range from 80 to 390 K with an interval of 5 K. The glass transition of BPBF₄ was observed at 194.09 K, the enthalpy and entropy of the glass transition were determined to be ΔH _g=2.157 kJ mol⁻¹ and ΔS _g=11.12 J K⁻¹ mol⁻¹, respectively. The result showed that the melting point of the BPBF₄ is 279.79 K, the enthalpy and entropy of phase transition were calculated to be ΔH _m = 8.453 kJ mol⁻¹ and ΔS _m=30.21 J K⁻¹ mol⁻¹. Using oxygen-bomb combustion calorimeter, the molar enthalpy of combustion of BPBF₄ was determined to be Δ_c H _m⁰ = −5451±3 kJ mol⁻¹. The standard molar enthalpy of formation of BPBF₄ was evaluated to be Δ_f H _m⁰ = −1356.3±0.8 kJ mol⁻¹ at T=298.150±0.001 K.     

Thermodynamics of sodium 5-methylisophthalic acid monohydrate and sodium isophthalic acid hemihydrate

Two crystal samples, sodium 5-methylisophthalic acid monohydrate (C₉H₆O₄Na₂·H₂O, s) and sodium isophthalic acid hemihydrate (C₈H₄O₄Na₂·1/2H₂O, s), were prepared from water solution. Low-temperature heat capacities of the solid samples for sodium 5-methylisophthalic acid monohydrate (C₉H₆O₄Na₂·H₂O, s) and sodium isophthalic acid hemihydrate (C₈H₄O₄Na₂·1/2H₂O, s) were measured by a precision automated adiabatic calorimeter over the temperature range from 78 to 379 K. The experimental values of the molar heat capacities in the measured temperature region were fitted to a polynomial equation on molar heat capacities (C _p,m) with the reduced temperatures (X), [X = f(T)], by a least-squares method. Thermodynamic functions of the compounds (C₉H₆O₄Na₂·H₂O, s) and (C₈H₄O₄Na₂·1/2H₂O, s) were calculated based on the fitted polynomial equation. The constant-volume energies of combustion of the compounds at T = 298.15 K were measured by a precise rotating-bomb combustion calorimeter to be Δ_c U(C₉H₆O₄Na₂·H₂O, s) = −15428.49 ± 4.86 J g⁻¹ and Δ_c U(C₈H₄O₄Na₂·1/2H₂O, s) = −13484.25 ± 5.56 J g⁻¹. The standard molar enthalpies of formation of the compounds were calculated to be Δ _f H _m ^θ (C₉H₆O₄Na₂·H₂O, s) = −1458.740 ± 1.668 kJ mol⁻¹ and Δ _f H _m ^θ (C₈H₄O₄Na₂·1/2H₂O, s) = −2078.392 ± 1.605 kJ mol⁻¹ in accordance with Hess’ law. The standard molar enthalpies of solution of the compounds, Δ _sol H _m ^θ (C₉H₆O₄Na₂·H₂O, s) and Δ _sol H _m ^θ (C₈H₄O₄Na₂·1/2H₂O, s), have been determined as being −11.917 ± 0.055 and −29.078 ± 0.069 kJ mol⁻¹ by an RD496-2000 type microcalorimeter. In addition, the standard molar enthalpies of hydrated anion of the compounds were determined as being Δ _f H _m ^θ (C₉H₆O₄ ²⁻, aq) = −704.227 ± 1.674 kJ mol⁻¹ and Δ _f H _m ^θ (C₈H₄O₄Na₂ ²⁻, aq) = −1483.955 ± 1.612 kJ mol⁻¹, from the standard molar enthalpies of solution and other auxiliary thermodynamic data through a thermochemical cycle.     

Some thermodynamic aspects of nitrides in materials science

The energies of combustion in fluorine of gallium nitride and indium nitride in wurzite crystalline structure have been measured in a two-compartment calorimetric bomb, and new standard molar enthalpies of formation have been calculated: Δ_fH_m⁰(GaN(cr) 298.15 K)= –(163.7±4.2) kJ mol^–1 and Δ_fH_m⁰(InN(cr) 298.15 K)= –(146.5±4.6) kJ mol^–1 . Comparison with the recommended values of the Δ_fH_m⁰ nitrides from the literature is also presented.     

Standard molar enthalpies of formation and sublimation of <Emphasis Type="Italic">N</Emphasis>-phenylphthalimide

The standard (p ⁰=0.1 MPa) molar enthalpy of formation, Δ_f H ⁰ _m, for crystalline N-phenylphthalimide was derived from its standard molar enthalpy of combustion, in oxygen, at the temperature 298.15 K, measured by static bomb-combustion calorimetry, as –206.0±3.4 kJ mol^–1. The standard molar enthalpy of sublimation, Δ^g _cr H ⁰ _m , at T=298.15 K, was derived, from high temperature Calvet microcalorimetry, as 121.3±1.0 kJ mol^–1. The derived standard molar enthalpy of formation, in the gaseous state, is analysed in terms of enthalpic increments and interpreted in terms of molecular structure.     

Thermochemical studies of phthalimide and two N-alkylsubstituted phthalimides (ALKYL=ETHYL AND n-PROPYL)

The standard (p⁰=0.1 MPa) molar enthalpies of formation, Δ_fH_m⁰, for crystalline phthalimides: phthalimide, N-ethylphthalimide and N-propylphthalimide were derived from the standard molar enthalpies of combustion, in oxygen, at the temperature 298.15 K, measured by static bomb-combustion calorimetry, as, respectively, – (318.0±1.7), – (350.1±2.7) and – (377.3±2.2) kJ mol^–1. The standard molar enthalpies of sublimation, Δ_cr^gH_m⁰, at T=298.15 K were derived by the Clausius-Clapeyron equation, from the temperature dependence of the vapour pressures for phthalimide, as (106.9±1.2) kJ mol^–1 and from high temperature Calvet microcalorimetry for phthalimide, N-ethylphthalimide and N-propylphthalimide as, respectively, (106.3±1.3), (91.0±1.2) and (98.2±1.4) kJ mol^–1. The derived standard molar enthalpies of formation, in the gaseous state, are analysed in terms of enthalpic increments and interpreted in terms of molecular structure.     

Thermodynamic properties of Ni-Ga melts

The partial mixing enthalpies of the components (Δ_m $ \bar H $ \bar H _i ) of the Ni-Ga melts were measured using the high-temperature isoperibolic calorimetry at 1770 ± 5 K in wide concentration interval. The limiting partial mixing enthalpy of gallium in a liquid nickel (Δ_m $ \bar H $ \bar H _Ga^∞) is −95.5 ± 19.8 kJ mol⁻¹, and similar function of nickel in liquid gallium (Δ_m $ \bar H $ \bar H _Ni^∞) is −74.5 ± 16.4 kJ mol⁻¹. The integral mixing enthalpy of liquid alloys of this system was calculated from partial enthalpies for the whole concentration area (Δ_m H _min = −32.1 ± 2.7 kJ mol⁻¹ at x _Ni = 0.5). The Δ_m H value of liquid nickel-gallium alloys independence of the temperature is confirmed. Enthalpies of formation of liquid (Δ_m H) phases of Ni-Ga system were compared with ones for solid (Δ_f H) phases of this system. An analysis of d-metals influence on formation energy of Ga-d-Me melts was made using the values of Δ_f H for intermediate phases of these systems. The article was translated by the authors.     

Standard molar enthalpies of formation of [RE(Gly)<Subscript>4</Subscript>(Im)(H<Subscript>2</Subscript>O)](ClO<Subscript>4</Subscript>)<Subscript>3</Subscript> (<Emphasis Type="Italic">RE</Emphasis>=Eu,Sm)

The two complexes, [RE(Gly)₄(Im)(H₂O)](ClO₄)₃(s)(RE = Eu, Sm), have been synthesized and characterized. The standard molar enthalpies of reaction for the following reactions, RECl₃·6H₂O(s)+4Gly(s)+Im(s)+3NaClO₄(s) = =[RE(Gly)₄(Im)(H₂O)](ClO₄)₃(s)+3NaCl(s)+5H₂O(l), were determined by solution-reaction colorimetry. The standard molar enthalpies of formation of the two complexes at T = 298.15 K were derived as Δ_f H _m^Θ {Eu(Gly)₄(Im)(H₂O)}(ClO₄)₃(s)} = = −(3396.6±2.3) kJ mol⁻¹ and Δ_f H _m^Θ {Sm(Gly)₄(Im)(H₂O)}(ClO₄)₃(s)} = −(3472.7±2.3) kJ mol⁻¹, respectively.     

Low-temperature heat capacities and standard molar enthalpy of formation of aspirin

Molar heat capacities (C _p,m) of aspirin were precisely measured with a small sample precision automated adiabatic calorimeter over the temperature range from 78 to 383 K. No phase transition was observed in this temperature region. The polynomial function of C _p,m vs. T was established in the light of the low-temperature heat capacity measurements and least square fitting method. The corresponding function is as follows: for 78 K≤T≤383 K, C _p,m/J mol^-1 K^-1=19.086X ⁴+15.951X ³-5.2548X ²+90.192X+176.65, [X=(T-230.50/152.5)]. The thermodynamic functions on the base of the reference temperature of 298.15 K, {ΔH _T -ΔH _298.15} and {S _T-S _298.15}, were derived. Combustion energy of aspirin (Δ_c U _m) was determined by static bomb combustion calorimeter. Enthalpy of combustion (Δ_c H ^o _m) and enthalpy of formation (Δ_f H ^o _m) were derived through Δ_c U _m as - (3945.26±2.63) kJ mol^-1 and - (736.41±1.30) kJ mol^-1, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

A thermochemical study of the coordination reactions of La(III) with alanine and glycine

The solid-state coordination reactions of lanthanum chloride with alanine and glycine, and lanthanum nitrate with alanine have been studied by classical solution calorimetry. The molar dissolution enthalpies of the reactants and the products in 2 mol L^-1 HCl solvent of these three solid-solid coordination reactions have been measured using an isoperibol calorimeter. From the results and other auxiliary quantities, the standard molar formation enthalpies have been determined to be Δ_f H _m ^θ[La(Ala)₃Cl₃·3H₂O(s), 298.2 K]= -3716.3 kJ mol^-1, Δ_f H _m ^θ [La(Gly)₃Cl₃·5H₂O(s), 298.2 K]= -4223.0 kJ mol^-1 and Δ_f H _m ^θ [La(Ala)₄(NO₃)₃·H₂O(s), 298.2 K]= -3867.57 kJ mol^-1, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Complexation of [2.2]paracyclophane with β- and γ-cyclodextrins studied by HPLC and NMR

The NMR spectra of [2.2]paracyclophane with β- or γ-cyclodextrin in DMF-d₇ at room temperature do not show significant complexation, while HPLC of the complexes in mixed H₂O:alcohol solvents demonstrate complexation with different stoichiometries. At 243 K in DMF solution the H3 and H5 NMR signals of γ-cyclodextrin (but not β) exhibit complexation-induced chemical shifts denoting complex formation. According to HPLC, at room temperature the [2.2]paracyclophane complex with β-cyclodextrin in 20% H₂O:EtOH exhibits 1:2 stoichiometry with K ₁ = 1×10² ± 2, K ₂ = 9.0×10⁴ ± 2×10³ (K = 9×10⁶) while that with γ-cyclodextrin in 50% H₂O:MeOH exhibits 1:1 stoichiometry with K ₁ = 4×10³ ± 150 M⁻¹. Thermodynamic parameters for both complexes have been estimated from the retention time temperature dependence. For the β-cyclodextrin complexation at 25°C ΔG ⁰ _CD is −39.7 kJ mol⁻¹ while ΔH ⁰ _CD and ΔS ⁰ _CD are −88.2 kJ mol⁻¹ and −0.16 kJ mol⁻¹ K⁻¹. For γ-cyclodextrin, the corresponding values are ΔG ⁰ _CD = −20.5 kJ mol⁻¹, ΔH ⁰ _CD = −33.5 kJ mol⁻¹ and ΔS ⁰ _CD = −0.04 kJ mol⁻¹ K⁻¹.