Standard enthalpies of formation of 4-methylbiphenyl and 4,4′-dimethylbiphenyl

The energies of combustion of 4-methylbiphenyl and 4,4′-dimethylbiphenyl in the crystal state were measured in a precision calorimeter equipped with a self-sealing bomb at 298.15 K. The enthalpies of vaporization of these substances were measured in an isothermal heat-conducting Calvet microcalorimeter. Standard enthalpies of formation were calculated for 4-methylbiphenyl and 4,4′-dimethylbiphenyl in the crystal, liquid, and gas states.     

Standard molar enthalpies of formation and phase changes of Tetra-N-phenylbenzidine and 4,4′-Bis (N-carbazolyl)-1,1′-biphenyl

Journal of Thermal Analysis and Calorimetry - The values of the standard molar energies of combustion of Tetra-N-phenylbenzidine and 4,4′-Bis(N-carbazolyl)-1,1′-biphenyl in solid phase...     

Standard molar formation enthalpies of flower-like NH4CdPO4·H2O

Flower-like ammonium cadmium phosphate monohydrate was synthesized by solid-state reaction at low temperature and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscope, and elemental analysis. The product NH₄CdPO₄·H₂O was obtained with flower-like morphology by the addition of fatty alcohol-polyoxyethylene ether surface-active agent. Based on Hess??s law, thermochemical cycle was designed to determine the dissolution enthalpies of reactants and products using a solution-reaction isoperibol calorimeter at 298.15?K, and the molar reaction enthalpy was calculated on the basis of above dissolution enthalpies. With the aid of other auxiliary thermodynamic data, the standard molar formation enthalpy of the title compounds was concluded: $ \Updelta_{\text{f}} H_{\text{m}}^{-\!\!\!\!\circ} [{\text{NH}}_{4} {\text{CdPO}}_{4} \cdot {\text{H}}_{2} {\text{O}}] = ( - 1749.82 \pm 0.76)\; {\text{kJ}}\; {\text{mol}}^{ - 1} . $      

Energetic studies of urea derivatives: Standard molar enthalpy of formation of 3,4,4′-trichlorocarbanilide

Thermochemical and thermophysical studies have been carried out for crystalline 3,4,4′-trichlorocarbanilide. The standard (p° = 0.1 MPa) molar enthalpy of formation, at T = 298.15 K, for the crystalline 3,4,4′-trichlorocarbanilide (TCC) was experimentally determined using rotating-bomb combustion calorimetry, as ?(234.6 ± 8.3) kJ · mol^?1. The standard enthalpy of sublimation, at the reference temperature of 298.15 K, was measured by the vacuum drop microcalorimetric technique, using a High Temperature Calvet Microcalorimeter as (182.1 ± 1.7) kJ · mol^?1. These two thermochemical parameters yielded the standard molar enthalpy of formation of the studied compound, in the gaseous phase, at T = 298.15 K, as ?(52.5 ± 8.5) kJ · mol^?1. This parameter was also calculated by computational thermochemistry at M05-2X/6-311++G7 and B3LYP/6-311++G(3df, 2p) levels, with a deviation less than 4.5 kJ · mol^?1 from experimental value. Moreover, the thermophysical study was made by differential scanning calorimetry, DSC, over the temperature interval between T = 263 K and its onset fusion temperature, T = (527.5 ± 0.4) K. A solid–solid phase transition was found at T = (428 ± 1) K, with the enthalpy of transition of (6.1 ± 0.1) kJ · mol^?1. The X-ray crystal structure of TCC was determined and the three-centred N–H?OC hydrogen bonds present analyzed.     

Standard enthalpies of formation of “A” type carbonate phosphobaryum hydroxyapatites

Phosphobaryum carbonate hydroxyapatites Ba₁₀(PO₄)₆(OH)_(2?2x)(CO₃) _x with 0????x????1, were synthesized in this study by solid gas reaction at a high temperature. Carbonate content was determined by thermogravimetric analysis and X-ray diffraction. The heat of the solution in a 3 wt% nitric acid solution was measured at 298?K using an isoperibol calorimeter. The combination of the enthalpies of solution with the enthalpies of formation of the reactants allowed us to determine the standard enthalpies of formation of the studied apatites. The result showed a decrease in formation enthalpy with the carbonate amount introduced in the lattice, suggesting an increase in stability of these compounds as the ratio of the substitution increases.     

Standard enthalpies of formation of α-aminobutyric acid and products of its dissociation in an aqueous solution

Heats of solution of crystalline α-aminobutyric acid in water and in aqueous solutions of potassium hydroxide at 298.15 K are measured by means of direct calorimetry. Standard enthalpies of formation of the amino acid and products of its dissociation in an aqueous solution are calculated.     

Standard enthalpies of formation of γ-aminobutyric acid and the products of its dissociation in aqueous solution

Heat effects of the dissolution of crystalline γ-aminobutyric acid in water and potassium hydroxide solutions are determined by direct colorimetry at 298.15 K. Standard enthalpies of formation of γ-aminobutyric acid and the products of its dissociation in aqueous solution are calculated.     

Standard enthalpies of formation of D,L-α-alanyl-glycine and the products of its dissociation in aqueous solutions

The heats of dissolution of crystalline D,L-α-alanyl-glycine in water and potassium hydroxide solutions were measured by direct calorimetry at 298.15 K using a calorimeter with an isothermal shell and automatic recording of the temperature-time curve.     

Standard formation enthalpies for α-amino acids: L-serine,L-arginine,and L-tyrosine

The energies of combustion, Δ _c U ⁰, of three amino acids: L-serine (I), L-arginine (II) and L-tyrosine (III) in the crystalline state at 298.15 K were determined using a static-bomb isoperibolic calorimeter. From these data, the enthalpies of combustion, Δ _c H ⁰, and the enthalpies of formation, Δ _f H ⁰, are calculated. The Δ _f H ⁰ values are compared with the published data.     

The standard enthalpies of formation of l-asparagine and l-α-glutamine

The energies of combustion of l-asparagine and l-α-glutamine were measured in a static bomb adiabatic calorimeter. Corrections were made for the heats due to the ignition of sample and for the nitric acid formation. The derived enthalpies of formation in solid state of asparagine monohydrate, nonhydrated asparagine and glutamine are respectively ?1084.1 ± 3.0, ?788.1 ± 4.7 and ?834.3 ± 4.6 kJ mol^?1. The data of enthalpy of formation are compared with the literature values and with estimated values by means of group additivity, using parameters recommended by Domalski and Hearing. The discrepancies between experimental and calculated values are explained by considering the number and strength of intermolecular hydrogen bonds. The dehydration of asparagine monohydrate and the possible melting of the three amino acids were investigated by means of DSC. Glutamine melts without considerable decomposition at about 182 °C, while asparagines decompose during the fusion process (208 °C).     

The estimation of ether’s enthalpies of formation

Taking hydrocarbon as gerneratrix, the differences of enthalpies of formation of ether and their corresponding generatrixes were compared and concluded and the equation to estimate ether’s enthalpy of formation, which was Δ_f H _e^°/(kJ/mol) = K(Δ_f H _m^ℴ − 90 + A) was obtained. The results can be elucidated with bond dissociation energies data, bond-enthalpy of formation method, induction effect and conjugative effect. The more essential account to explain the results can be got by using quantum chemistry theories, etc. Using replacement and comparison method, the way of estimation of organic compounds’ thermodynamic properties including enthalpy of formation can be obtained either. The article is published in the original.     

Standard enthalpies of formation of Ce–Au congruent compounds (CeAu,CeAu2, and Ce14Au51)

The enthalpies of formation of Ce–Au congruent compounds (CeAu, CeAu₂, and Ce₁₄Au₅₁) have been determined at 1123 K and the standard enthalpies of formation at 298 K have been deduced from the measurements of enthalpy increments of single-phase samples. The following values (kJ/mole of atoms) are reported: Δ_fH°_1123 K (CeAu) = −75.2 ± 1.4, Δ_fH°_298 K (CeAu) = −76.2 ± 1.9, Δ_fH°_1123 K (CeAu₂) = −71.3 ± 2.0, Δ_fH°_298 K (CeAu₂) = −70.3 ± 2.2, Δ_fH°_1123 K (Ce₁₄Au₅₁) = −55.0 ± 1.7, and Δ_fH°_298 K (Ce₁₄Au₅₁) = −53.2 ± 1.9.     

Characterization and crystal structures of solvated N′-(4-hydroxy-3-nitrobenzylidene)-3-methylbenzohydrazide and N′-(4-dimethyl-aminobenzylidene)-3-methylbenzohydrazide

Two new solvated benzohydrazone derivatives N′-(4-hydroxy-3-nitrobenzylidene)-3-methylbenzohydrazide-methanol-water (2/1/1) 2(C₁₅H₁₃N₃O₄)·CH₃OH·H₂O (1) and N′-(4-dimethylamino-benzylidene)-3-methylbenzohydrazide methanol monosolvate C₁₇H₁₉N₃O·CH₃OH (2) are prepared and characterized by elemental analysis, ¹H and ¹³C NMR, and single crystal X-ray diffraction. Compound 1 crystallizes in the monoclinic space group P2₁/c with unit cell dimensions a = 17.084(2) Å, b = 12.706(1) Å, c = 15.412(1) Å, β = 113.207(1)°, V = 3074.1(4) ų, Z = 4, R ₁ = 0.0567, and wR ₂ = 0.1209. Compound 2 crystallizes in the monoclinic space group P2₁/n with unit cell dimensions a = 15.058(1) Å, b = 6.658(1) Å, c = 17.211(2) Å, β = 94.189(2)°, V = 1720.8(3) ų, Z = 4, R ₁ = 0.0611, and wR ₂ = 0.1594. X-ray diffraction indicates that the asymmetric unit of 1 contains two independent benzohydrazone molecules, one methanol and one water molecules. The asymmetric unit of 2 contains one benzohydrazone molecule and one methanol molecule. Benzohydrazone molecules of the compounds display trans configurations with respect to the C=N double bonds. The crystal structures of the compounds are stabilized by hydrogen bonds and weak π...π interactions.     

Standard enthalpies of formation of bis(β-diketonate)cobalt(II) complexes: The mean (CoO) bond-dissociation enthalpies

The standard enthalpies of formation, at 298 K, of the 1-phenyl-1,3-butanedione (HBZAC) and 1,1,1-trifluoro-2,4-pentanedione (HTFAC) crystalline complexes of cobalt(II) were determined by precise solution—reaction calorimetry: ΔH⁰_f{Co(BZAC)₂,cr} = −632±6.0 kJ mol⁻¹ ΔH⁰_f{Co(TFAC)₂,cr} = −2140±10 kJ mol⁻¹. The average molar bond-dissociation enthalpies, <D>(CoO) were derived.     

Determinations of combustion and formation enthalpies of C_(60)and C_(70)

Ｆｕｌｌｅｒｅｎｅｓａｒｅａｋｉｎｄｏｆｃａｒｂｏｎａｌｌｏｔｒｏｐｅｓｆｏｕｎｄｒｅｃｅｎｔｌｙ,ａｎｄｈａｖｅｄｉｓｔｉｎｃｔｉｖｅｓｔｒｕｃｔｕｒｅｓａｎｄｐｒｏｐｅｒｔｉｅｓ.Ｆｏｒｅｘａｍｐｌｅ,Ｃ60ｈａｓａｆｏｏｔｂａｌｌｌｉｋｅｃａｒｂｏｎｓｋｅｌｅｔｏｎｗｉｔｈ20ｓｉｘｍｅｍｂｅｒｅｄｒｉｎｇｓ,12ｆｉｖｅｍｅｍｂｅｒｅｄｒｉｎｇｓａｎｄａｌａｒｇｅｂａｌｌｓｈｅｌｌｌｉｋｅπｂｏｎｄｓｙｓｔｅｍ.Ａｌｔｅｒｎａｔｉｖｅｌｙ,Ｃ70ｈａｓａｎｅｌｌｉｐｓｏｉｄｌｉｋｅｃａｒｂｏｎｓｋｅｌ…     

Synthesis and Crystal Structure of 4-Phenyl-5-(1′- t-butyl-5′-methyl-4′-pyrazolyl)-1,2,4-triazol-3-thione

The crystal structure of 4-phenyl-5-(1′-t-butyl-5′-methyl-4′-pyrazolyl)-1,2,4-triazol- 3-thione 5 (C16H19N5S, Mr = 313.42) has been determined by single-crystal X-ray diffraction analysis. The crystal belongs to monoclinic, space group P21/c with a = 6.680(2), b = 27.44(1), c = 9.388(4)(A。), β = 106.738(6)°, V = 1648(1)(A。)3, Z = 4, Dc = 1.263 g/cm3, μ= 0.200 mm-1, F(000) = 664, R = 0.0608 and wR = 0.1176. The results confirmed that 5 can be assigned to the thione tautomeric form.     

Crystal structures,Hirshfeld analysis,and energy framework analysis of two differently 3′-substituted 4-methylchalcones: 3′-(N=CHC6H4-p-CH3)-4-methylchalcone and 3′-(NHCOCH3)-4-methylchalcone

Two crystal structures of chalcones, or 1,3-diarylprop-2-en-1-ones, are presented; both contain a p-methyl substitution on the 3-Ring, but differ with respect to the m-substitution on the 1-Ring. Their systematic names are (2E)-3-(4-methylphenyl)-1-(3-{[(4-methylphenyl)methylidene]amino}phenyl)prop-2-en-1-one (C₂₄H₂₁NO) and N-{3-[(2E)-3-(4-methylphenyl)prop-2-enoyl]phenyl}acetamide (C₁₈H₁₇NO₂), which are abbreviated as 3′-(N=CHC₆H₄-p-CH₃)-4-methylchalcone and 3′-(NHCOCH₃)-4-methylchalcone, respectively. Both chalcones represent the first reported acetamide-substituted and imino-substituted chalcone crystal structures, adding to the robust library of chalcone structures within the Cambridge Structural Database. The crystal structure of 3′-(N=CHC₆H₄-p-CH₃)-4-methylchalcone exhibits close contacts between the enone O atom and the substituent arene ring, in addition to C…C interactions between the substituent arene rings. The structure of 3′-(NHCOCH₃)-4-methylchalcone exhibits a unique interaction between the enone O atom and the 1-Ring substituent, contributing to its antiparallel crystal packing. In addition, both structures exhibit π-stacking, which occurs between the 1-Ring and R-Ring for 3′-(N=CHC₆H₄-p-CH₃)-4-methylchalcone, and between the 1-Ring and 3-Ring for 3′-(NHCOCH₃)-4-methylchalcone.