Enthalpies of formation of acetyl radicals

The database on the enthalpies of formation (Δ_f H ^○) of aliphatic acetyl radicals of the RC·(O) type is analyzed and extended. Δ_f H ^○ values are estimated for the first time for three compounds on the basis of experimental data. The data were analyzed using the additive group approach with the determination and correction of parameters. Good correspondence between the Δ_f H ^○(RC·(O)) values calculated according to parameters with experimental data is observed.     

Enthalpy of the formation of natural hydrous aluminum hydroxosulfate (aluminite)

A thermochemical study of natural aluminum hydroxosulfate Al₂[(OH)₄SO₄] · 7H₂O, aluminite (Nakhodka deposit, West Chukotka, Russia) is performed on a Tian-Calvet “Setaram” high-temperature heat-conducting microcalorimeter (France). The enthalpy of aluminite formation from simple compounds is obtained via the melt calorimetry of dissolution, Δ_f H ^○(298.15 K) = ?4986 ± 21 kJ/mol.     

Influence of the molecular weight of polystyrene on its thermodynamic properties

The thermodynamic properties of a series of polystyrene samples with different molecular weights (M _w was varied from 2.5·10³ to 6.57·10⁴) were studied by precision adiabatic vacuum, high-accuracy dynamic, and combustion calorimetry: temperature dependences of the heat capacity in a wide temperature range, thermodynamic characteristics of glass transition and glassy state under standard pressure, and energy of combustion. The thermodynamic functions C ^○ _p (T), H ^○(T) - H ^○(0), S ^○(T) - S ^○(0), and G ^○(T) - H ^○(0) of polystyrene with different molecular weights, enthalpies of combustion Δ_c H ^○, thermodynamic parameters of formation from simple substances Δ_f H ^○, Δ_f S ^○, and Δ_f G ^○ at T = 298.15 K, and parameters of their synthesis from monomers were calculated from the experimental data. The temperature dependences of the heat capacity for a region of 0–380 K, glass transition temperatures, and thermodynamic characteristics of formation and synthesis of polystyrene depending on its molecular weight were examined.     

Effect of solvation on the thermodynamics of formation for 18-crown-6 ether complexes with glycine and triglycine in water-ethanol solutions at 298 K

Using data from calorimetric titration, standard thermodynamic parameters logK ^○, Δ_r G ^○, Δ_r H ^○, and TΔ_r S ^○ of the formation of 18-crown-6 ether (18C6) molecular complex with triglycine (3Gly), [3Gly18C6] in H₂O-EtOH solvents with contents of ethanol x ranging between 0.0 and 0.5 mole fractions are calculated. Increasing the concentration of EtOH in the solvent is found to raise the reaction’s exothermicity from ?5.9 to ?21.0 kJ mol^?1 and logK ^○ [3Gly18C6] from 1.10 to 2.53. A comparative analysis of the effect the composition of H₂O-EtOH solvent has on the reactions of [3Gly18C6] and [Gly18C6] formation is performed. As in case of [Gly18C6] formation, the changes in the complex’s enthalpy of solvation Δ_tr H ^○([3Gly18C6]) are close to the Δ_tr H ^○(18C6) parameter and differ considerably from the Δ_tr H ^○(3Gly) value, testifying to the crucial role 18C6 plays in changing the [3Gly18C6] state of solvation. The ratio between solvation contributions from reagents to Δ_tr G ^○ of [3Gly18C6] formation is found to differ from that the one between the corresponding contributions to Δ_tr H _r ^o : in transferring from water to H₂O-EtOH mixtures, the increase in the positive Δ_tr G ^○(18C6) values is slight and therefore negligible when compared to Δ_tr G ^○(3Gly).     

Determination of enthalpies of formation of organic free radicals from bond dissociation energies 1. Hydrocarbon radicals

The enthalpies of formation (ΔH _f ^o) for 24 hydrocarbon radicals (R^?), mainly polycyclic aromatic radicals with the complex structure, were determined from the published data on bond dissociation energies. The ΔH _f ^o values of the corresponding molecules were calculated, in the majority of cases, by the macroincrement method. Calculations by the group contribution method were performed. Some ΔH _f ^o(R^?) values were compared to those calculated by the additive-group method. Calculations were performed, and the conjugation energies of the radicals were discussed. The errors of determination of the ΔH _f ^o(R^?) values found were estimated. Due to this work, the database for ΔH _f ^o values of hydrocarbon radicals was increased more than by 25%.     

Effect of the composition of a solution on the enthalpies of solvation of piperidine in methanol-acetonitrile and dimethylsulfoxide-acetonitrile mixed solvents

Heat effects of dissolution of piperidine (ppd) are measured by calorimetry at 298.15 K over the range of composition of acetonitrile-methanol (AN-MeOH) mixed solvents. Based on the Δ_sol H ^○(ppd)_AN-MeOH values obtained using the literature data on Δ_sol H ^○ (ppd) in acetonitrile-dimethylsulfoxide (AN-DMSO) mixed solvents and the vaporization enthalpy of ppd, the enthalpies of solvation of amine in AN-MeOH and AN-DMSO binary mixtures are calculated. A rise in the exothermicity of solvation of piperidine is observed upon the transition from AN to DMSO and MeOH, due mainly to the enhanced solvation of the amino group of ppd as a result of changes in the acid-base properties of the mixed solvent.     

Enthalpy pair coefficients of interaction for DL-valine in aqueous solutions of polyatomic alcohols at 298 K

Integral enthalpies of dissolution Δ_sol H ^m of DL-valine are measured via calorimetry of dissolution in aqueous solutions of glycerol, ethylene glycol, and 1,2-propylene glycol. Standard values of the enthalpies of dissolution (Δ_sol H ^○) and transfer (Δ_tr H ^○) of amino acid from water to mixed solvent are calculated from the resulting experimental data. The enthalpy coefficients for pair interactions h_xy of amino acid with polyatomic alcohol molecules are calculated using the McMillan-Meyer theory and have positive values. The obtained results are discussed in light of the theory of the predomination of various types of interactions in mixed solutions and the effect of structural features of interacting biomolecules on the thermochemical parameters of the dissolution of amino acids.     

Thermodynamics of the formation of nickel(II) complexes with L-histidine in aqueous solutions

The heat effects of the formation of Ni(II) complexes with L-histidine in an aqueous solution are determined via direct calorimetry at 298.15 K and ionic strengths of 0.2, 0.5, and 1.0 (KNO₃). The standard thermodynamic characteristics (Δ_r H ^○, Δ_r G ^○, Δ_r S ^○) of complex formation in the investigated system are calculated. It is concluded that the resulting values are consistent with the results from studying the structure of L-histidine complexes with Ni²⁺ ions by various spectral methods.     

Thermal decomposition of zinc and cadmium zirconyl oxalates

The enthalpy of formation at 298.15 K of the polymer Al₁₃O₄(OH)₂₈(H₂O)³⁺₈ and an amorphous aluminium trihydroxide gel was studied using an original differential calorimetric method, already developed for adsorption experiments, and aluminium-27 NMR spectroscopy data. ΔH_f “Al₁₃” (298.15 K) = ? 602 ± 60.2 kJ mole^?1 and ΔH_f Al(OH)₃ (298.15 K) = ? 51 ± 5 kJ mole^?1. Using theoretical values of ΔG_R “Al₁₃” and ΔG_R Al(OH)₃, we calculated ΔG_f “Al₁₃” (298.15 K) = ? 13282 kJ mole^?1; ΔS_f “Al₁₃” (298.15 K) = + 42.2 kJ mole^?1; ΔG_f Al(OH)₃ (298.15 K) = ? 782.5 kJ mole^?1; and ΔS_f Al(OH)₃ (298.15 K) = + 2.4 kJ mole^?1.     

Energetics of the molecular interactions of L-alanine and L-serine with xylitol, D-sorbitol, and D-mannitol in aqueous solutions at 298.15 K

Integral enthalpies of dissolution Δ_sol H ^m of L-alanine and L-serine are measured via the calorimetry of dissolution in aqueous solutions of xylitol, D-sorbitol, and D-mannitol. Standard enthalpies of dissolution (Δ_sol H ^○) and the transfer (Δ_tr H ^○) of amino acids from water to binary solvent are calculated from the experimental data. Using the McMillan-Mayer theory, enthalpy coefficients of pairwise interactions h _xy of amino acids with molecules of polyols are calculated that are negative. The obtained results are discussed within the theory of the prevalence of different types of interactions in mixed solutions and the effect of the structural features of interacting biomolecules on the thermochemical parameters of dissolution of amino acids.     

Correlation between the properties of a compound and the polynomial coefficients of a molecular Graph’s adjacency matrix

An additive scheme with 11 constants is derived from the coefficients of characteristic polynomials (CCPs) of adjacency matrix A of irregular molecular graphs (IMG) for molecules that contain a bivalent heteroatom -SH or -OH at the beginning of the chain. The structural significance of the CCPs to adjacency matrix A′ is established. Our formula is used to calculate the enthalpies of formation Δ_f H _{liq 298K} ^○ of liquid alkanethiols (mercaptanes) C _n H_{2n + 1}SH and Δ_f H _{liq 298K} ^○ of liquid saturated monoalcohols C _n H_{2n + 1}OH that remain unstudied experimentally.     

The enthalpy of formation of the praseodymium ion (3+) in an infinitely dilute aqueous solution

The enthalpy of reaction between praseodymium metal and 1.07 n HCl and the enthalpy of solution of praseodymium trichloride in 1.07 n HCl and water were measured in a swinging isoperibol calorimeter at 298.15 K. The results were used to calculate the enthalpy of formation of the praseodymium ion in the state of an infinitely dilute aqueous solution, Δ_f H°_298.15 Pr³⁺(sln, ∞H₂O) = ?687.8 ± 1.7 kJ/mol.     

Enthalpies of the formation of aliphatic carbonyl-containing radicals

A collection of data on enthalpies of the formation(Δ_f H ^o) of aliphatic carbonyl-containing radicals is analyzed and expanded. The Δ_f H ^o values for 29 carbonyl-containing radicals are determined for the first time, and are strongly revised for 17 carbonyl-containing radicals using the literature data on the dissociation energies of the bonds in molecules. The data is analyzed on the basis of the structureproperty (enthalpy of formation) relation within the additive-group approach, with the determination and specification of the parameters. It is concluded that the Δ_f H ^o values of carbonyl-containing radicals calculated from the obtained parameters (a total of 96 compounds was considered) agree well with the experimental data.     

Standard enthalpy of formation of crystalline Ca[NiF6]

The enthalpies of reaction of crystalline Ca[NiF₆](cryst.) with water and a diluted solution of alkali are measured at 298.15 K using an isothermal-shell calorimeter. Based on the obtained values and literature data and using two independent methods, the standard enthalpy of formation of the studied compound is determined (Δ_f H ^○Ca[NiF₆](cryst.) = ?1955 ± 7 kJ/mol).     

Standard thermochemical characteristics of formation of triphenylantimony bis(acetophenoneoximate)

For the first time, the energy of combustion Δ_c U of crystalline triphenylantimony bis(acetophenoneoximate) Ph₃Sb(ONCPhMe)₂ has been measured at T = 298.15 K using the isothermal combustion calorimeter with a stationary bomb. The standard molar enthalpy of combustion Δ_c Hº, the standard molar enthalpy Δ_f Hº, and free Gibbs energy Δ_f Gº of formation of the above oximate have been calculated.     

Hexadecyltrimethylammonium bromide micellization in glycine,diglycine, and triglycine aqueous solutions as a function of surfactant concentration and temperatures

Micellization behavior of hexadecyltrimethylammonium bromide (HTAB) was investigated conductometrically in aqueous solutions containing 0.02 mol kg^?1glycine (Gly), diglycine (Gly-Gly), and triglycine (Gly-Gly-Gly) as a function of surfactant concentration at different temperatures. The critical micelle concentration (CMC) of HTAB exhibits a decreasing trend as the number of carbon atoms increases from Gly to Gly-Gly-Gly, favoring the micelle formation. The values of CMC and the degree of counterion dissociation of the micelles were utilized to evaluate the standard free energy for transferring the surfactant hydrophobic chain out of the solvent to the interior of the micelle, ΔG _HP ^○ , free energy associated with the surface contributions, ΔG _S ^○ , standard free energy, ΔG _m ^○ , enthalpy, ΔH _m ^○ , and entropy, ΔS _m ^○ of micellization were also calculated. The results show that the micellization of HTAB in aqueous solutions as well as in aqueous Gly/Gly-Gly/Gly-Gly-Gly solutions is primarily governed by the entropy gain due to the transfer of the hydrophobic groups of the surfactant from the solvent to the interior part of the micelle. The CMC obtained by fluorometric method is in close agreement with those obtained conductometrically. Furthermore, decrease in the I ₁/I ₃ ratio of pyrene fluorescence intensity suggests the solubilization of the additives by the surfactant micelles and that this solubilization increases as the hydrophobicity increases from Gly to Gly-Gly-Gly.     

The standard enthalpies of formation of alkoxy-NNO-azoxy compounds

The standard enthalpies of combustion Δ_c H ^o and formation Δ_f H ^o of seven alkoxy-NNO-azoxy compounds containing the-N⁺(O^?)=NO-characteristic group were determined by combustion in a calorimetric bomb in the atmosphere of oxygen. The contribution of this group to the Δ_f H ^o enthalpies of the substances studied was calculated. The Δ_f H ^o enthalpies found by the method of group contributions were in satisfactory agreement with experimental data.     

Thermodynamic study of complex formation between Kryptofix-5 and Sn2+ in several individual and binary non-aqueous solvents using a conductometric method

The complex formation between 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (Kryptofix-5) and Sn²⁺ ions was studied in pure acetonitrile (AN), dimethylformamide (DMF), 1,4-dioxane (DOX), and methanol (MeOH) and in acetonitrile-1,4-dioxane (AN-DOX), acetonitrile-dichloromethane (AN-DCM), acetonitrile-methanol (AN-MeOH), and acetonitrile-dimethylformamide (AN-DMF) binary mixed solvent solutions at different temperatures using conductometric method. 1: 1 [ML] complex is formed between the metal cation and ligand in most solvent systems but in the cases of AN-MeOH (MeOH = 90 mol %) binary mixture and in pure MeOH a 2: 1 [M₂L] complex was observed, that is the stoichiometry of complexes may be changed by the nature of the medium. The stability order of the (Kryptofix-5·Sn)²⁺ complex in the studied binary mixed solvent solutions at 25°C was found to be AN-DOX > AN-DCM > AN-MeOH > AN-DMF and in the case of pure solvents at 25°C the sequence was the following: AN > DMF > DOX. A non-linear behavior was observed for changes of logK _f of (Kryptofix-5·Sn)²⁺ complex versus the composition of the binary mixed solvents, which was explained in terms of solvent-solvent intractions and also by the preferential solvation of the f species involved in the complexation reaction. The values of standard enthalpy changes (ΔH _c ^○ ) for complexation reactions were obtained from the slope of the Van’t Hoff plots and the changes in standard entropy (ΔS _c ^○ ) were calculated from the relationship ΔG _{c, 298.15} ^○ = ΔH _c ^○ ? 298.15ΔS _c ^○ . The results show that in most cases, the (Kryptofix-5·Sn)²⁺ complex is both enthalpy and entropy stabilized.     

Thermodynamique de substances azotees. IX. Etude thermochimique de la benzamide. Comparaison des grandeurs energetiques liees a la structure de quelques amides et thioamides

The enthalpy of sublimation of benzamide was obtained by calorimetry in the range 323<T (K)<350. From values of ΔH_sub(T)=f(T), it was possible to determine ΔH⁰_sub (298.15 K)=101.7±1.0 kJ mole^?1. Using previous data on ΔH⁰_f (c, 298.15 K) obtained by combustion calorimetry, the value of ΔH⁰_f (g, 298.15 K)=?100.9±1.2 kJ mole^?1 was calculated. With the use of energetical values concerning thioacetamide, thiobenzamide and thiourea, on the one hand, and acetamide, benzamide and urea, on the other, a comparative study was made.     

Enthalpy of formation of aqueous tungstate ion and of crystalline tungstic acid (H2WO4)

Calorimetric measurements of the enthalpy of reaction of WO₃(c) with excess OH^?(aq) have been made at 85°C. Similar measurements have been made with MoO₃(c) at both 85 and 25°C, to permit estimation of ΔH°=?13.4 kcal mol^?1 for the reaction WO₃(c)+2OH^?(aq)=WO^2?₄(aq)+H₂O(liq) at 25°C. Combination of this ΔH° with ΔH°_f for WO₃(c) leads to ΔH°_f=?256.5 kcal mol^?1 for WO^2?₄(aq). We also obtain ΔH°_f=?269.5 kcal mol^?1 for H₂WO₄(c). Both of these values are discussed in relation to several earlier investigations.