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Parabens (or esters of 4-hydroxybenzoic acid) are widely used as effective preservatives in cosmetic and pharmaceutical products. They are manufactured by the esterification of 4-hydroxybenzoic acid with the corresponding alcohol, these reactions taking place under thermodynamic control. It has turned out that the available thermodynamic data are in disarray. Thermochemical properties of a homological series of the alkyl 4-hydroxybenzoates (alkyl = methyl, ethyl, n -propyl and n -butyl) were studied by combustion calorimetry, transpiration, static method and DSC. The following experimental results were derived for alkyl 4-hydroxybenzoates (alkyl, Δ cr g H m o (298.15 K) and Δ f H m o (cr, 298.15 K, in kJ⋅mol −1 )): methyl, 107.9 ± 0.4 and − 563.6 ± 1.1; ethyl, 111.5 ± 0.4 and − 597.6 ± 1.2; n -propyl, 115.8 ± 0.5 and − 621.3 ± 1.7; and n -butyl, 122.9 ± 1.5 and − 651.8 ± 1.9. Experimental enthalpies of sublimation, vaporisation, fusion and enthalpies of formation in the crystalline state were derived. The vaporisation enthalpies of alkyl 4-hydroxybenzoates were tested for consistency and analysed for structure–property relationships. The composite quantum chemical methods G3MP2 and G4 were used to calculate the theoretical gas-phase enthalpies of formation in good agreement with the experiment. The data sets for each thermodynamic property were evaluated and recommended for thermochemical calculations. This study provides valuable insights into the thermodynamic properties of parabens and can help in the development of more accurate models to predict their behaviour in various applications.

Adsorption processes often include three important components: kinetics, isotherm, and thermodynamics. In the study of solid–liquid adsorption, “standard” thermodynamic equilibrium constant K Eq o ; dimensionless) plays an essential role in accurately calculating three thermodynamic parameters: the standard Gibbs energy change (∆G°; kJ/mol), the standard change in enthalpy (∆H°; kJ/mol), and the standard change in entropy [∆S°; J/(mol × K)] of an adsorption process. Misconception of the derivation of the K Eq o constant that can cause calculative errors in values (magnitude and sign) of the thermodynamic parameters has been intensively reflected through certain kinds of papers (i.e., letters to editor, discussions, short communications, and correspondence like comment/rebuttal). The distribution coefficient (K D) and Freundlich constant (K F) have been intensively applied for calculating the thermodynamic parameters. However, a critical question is whether K D or K F is equal to K Eq o . This paper gives (1) thorough discussion on the derivation of thermodynamic equilibrium constant of solid–liquid adsorption process, (2) reasonable explanation on the inconsistency of (direct and indirect) application of K D or K F for calculating the thermodynamic parameters based on the derivation of K Eq o , and (3) helpful suggestions for improving the quality of papers published in this field.

Information about the structure-property relationship can be useful for the synthesis of compounds with desired properties, analysis of the role of intermolecular interactions in various physicochemical processes and separation of the synthesis product from impurities. In the present work, the influence of the position of the carbonyl group on the saturated vapour pressure and enthalpy of vaporization of ketones was studied. The saturated vapour pressures of isomeric decanones, undecanones and isophorone were measured by the transpiration method. The enthalpies of vaporization of isomeric ketones were determined using various methods: solution calorimetry, transpiration and correlation gas chromatography. The obtained values agree with each other within 1 kJ mol −1 . It was shown that 2 - alkanones have higher enthalpies of vaporization and lower vapour pressures than 3-, 4-, 5-, 6-alkanones, which can be explained by the stronger intermolecular interactions existing between the molecules of 2-alkanones compared to others isomers.

The standard molar enthalpy of formation Δ f H 298.15 K ∘ of five ternary compounds in the Pb–V–O system, namely, PbV 2 O 6 (s), Pb 2 V 2 O 7 (s), Pb 3 V 2 O 8 (s), Pb 4 V 2 O 9 (s) and Pb 8 V 2 O 13 (s) were determined employing room temperature solution calorimetry and the values obtained are − 1842. 0 ± 1.0, − 2062.4 ± 2.3, − 2183.0 ± 4.0, − 2342.3 ± 3.2, − 3549.0 ± 5.0 kJ mol −1 , respectively. The enthalpy increment of these compounds were measured using a high temperature calvet calorimeter in the temperature range of 325–985 K. From the enthalpy increment data, the temperature dependence of molar heat capacities of these compounds was derived.

The complexity of problems in gas dynamics is increasing from year to year, which makes sequential computational codes more and more inadequate and brings the importance of creating their parallel implementations. The problem of building the parallel implementations is not simple, especially in case of parallelization of the existing sequential codes. In this paper we present a method of simulation of high-enthalpy flows and describe the peculiarities of its parallel implementation utilizing PETSc library, which gives a wide variety of tools to simplify creation of parallel codes. The results for calculation of OREX reentry module as well as analysis of scalability of the parallel code implementation are given.

Bond dissociation enthalpies (BDEs) of organic molecules play a fundamental role in determining chemical reactivity and selectivity. However, BDE computations at sufficiently high levels of quantum mechanical theory require substantial computing resources. In this paper, we develop a machine learning model capable of accurately predicting BDEs for organic molecules in a fraction of a second. We perform automated density functional theory (DFT) calculations at the M06-2X/def2-TZVP level of theory for 42,577 small organic molecules, resulting in 290,664 BDEs. A graph neural network trained on a subset of these results achieves a mean absolute error of 0.58 kcal mol −1 (vs DFT) for BDEs of unseen molecules. We further demonstrate the model on two applications: first, we rapidly and accurately predict major sites of hydrogen abstraction in the metabolism of drug-like molecules, and second, we determine the dominant molecular fragmentation pathways during soot formation. Bond dissociation enthalpies are key quantities in determining chemical reactivity, their computations with quantum mechanical methods being highly demanding. Here the authors develop a machine learning approach to calculate accurate dissociation enthalpies for organic molecules with sub-second computational cost.

In the fast-evolving field of halide perovskite semiconductors, the 2D perovskites (A′)₂(A)n−1M n X3n+1 [where A = Cs⁺, CH₃NH₃⁺, HC(NH₂)₂⁺; A′ = ammonium cation acting as spacer; M = Ge2+, Sn2+, Pb2+; and X = Cl⁻, Br⁻, I⁻] have recently made a critical entry. The n value defines the thickness of the 2D layers, which controls the optical and electronic properties. The 2D perovskites have demonstrated preliminary optoelectronic device lifetime superior to their 3D counterparts. They have also attracted fundamental interest as solution-processed quantum wells with structural and physical properties tunable via chemical composition, notably by the n value defining the perovskite layer thickness. The higher members (n > 5) have not been documented, and there are important scientific questions underlying fundamental limits for n. To develop and utilize these materials in technology, it is imperative to understand their thermodynamic stability, fundamental synthetic limitations, and the derived structure–function relationships. We report the effective synthesis of the highest iodide n-members yet, namely (CH₃(CH₂)₂NH₃)₂(CH₃NH₃)₅Pb₆I19 (n = 6) and (CH₃(CH₂)₂NH₃)₂(CH₃NH₃)₆Pb₇I22 (n = 7), and confirm the crystal structure with single-crystal X-ray diffraction, and provide indirect evidence for “(CH₃(CH₂)₂NH₃)₂(CH₃NH₃)₈Pb₉I28” (“n = 9”). Direct HCl solution calorimetric measurements show the compounds with n > 7 have unfavorable enthalpies of formation (ΔH f), suggesting the formation of higher homologs to be challenging. Finally, we report preliminary n-dependent solar cell efficiency in the range of 9–12.6% in these higher n-members, highlighting the strong promise of these materials for high-performance devices.

We have developed an analytical method to quantitatively analyze differential scanning calorimetry (DSC) experimental data. This method provides accurate determination of thermal properties such as equilibrium melting temperature, latent heat, change of heat capacity which can be performed automatically without intervention of a DSC operator. DSC is one of the best techniques to determine the thermal properties of materials. However, the accuracy of the transition temperature and enthalpy change can be affected by artifacts caused by the instrumentation, sampling, and the DSC analysis methods which are based on graphical constructions. In the present study, an analytical function (DSC N (T)) has been developed based on an assumed Arrhenius crystal size distribution together with instrumental and sample-related peak broadening. The DSC N (T) function was successfully applied to fit the experimental data of a substantial number of calibration and new unknown samples, including samples with an obvious asymmetry of the melting peak, yielding the thermal characteristics such as melting and glass transition temperature, and enthalpy and heat capacity change. It also allows very accurate analysis of binary systems with two distinct but severely overlapping peaks and samples that include a cold crystallization before melting.

The present work is focused on determining the enthalpy of formation of several derivatives of amino-1,2,4-triazoles. Experimentally, the enthalpies of formation of the crystalline phase and the enthalpies of sublimation of 3-amino- and 3,5-diamino-1 H -1,2,4-triazole were derived, respectively, from static-bomb combustion calorimetry and Calvet microcalorimetry or Knudsen effusion measurements. For 4-amino-4 H -1,2,4-triazole, only the enthalpy of sublimation was measured. Gas-phase standard molar enthalpies of formation were also estimated using theoretical calculations performed with the G3(MP2) composite approach. The very good agreement of these estimates with the experimental results, support the extension of this study to the estimate of this property for the remaining compounds not studied experimentally. The results obtained are interpreted in terms of structural contributions.

The calculation of the standard enthalpies of vaporization, sublimation and solvation of organic molecules is presented using a common computer algorithm on the basis of a group-additivity method. The same algorithm is also shown to enable the calculation of their entropy of fusion as well as the total phase-change entropy of liquid crystals. The present method is based on the complete breakdown of the molecules into their constituting atoms and their immediate neighbourhood; the respective calculations of the contribution of the atomic groups by means of the Gauss-Seidel fitting method is based on experimental data collected from literature. The feasibility of the calculations for each of the mentioned descriptors was verified by means of a 10-fold cross-validation procedure proving the good to high quality of the predicted values for the three mentioned enthalpies and for the entropy of fusion, whereas the predictive quality for the total phase-change entropy of liquid crystals was poor. The goodness of fit (Q2) and the standard deviation (σ) of the cross-validation calculations for the five descriptors was as follows: 0.9641 and 4.56 kJ/mol (N = 3386 test molecules) for the enthalpy of vaporization, 0.8657 and 11.39 kJ/mol (N = 1791) for the enthalpy of sublimation, 0.9546 and 4.34 kJ/mol (N = 373) for the enthalpy of solvation, 0.8727 and 17.93 J/mol/K (N = 2637) for the entropy of fusion and 0.5804 and 32.79 J/mol/K (N = 2643) for the total phase-change entropy of liquid crystals. The large discrepancy between the results of the two closely related entropies is discussed in detail. Molecules for which both the standard enthalpies of vaporization and sublimation were calculable, enabled the estimation of their standard enthalpy of fusion by simple subtraction of the former from the latter enthalpy. For 990 of them the experimental enthalpy-of-fusion values are also known, allowing their comparison with predictions, yielding a correlation coefficient R2 of 0.6066.