Predicting the enthalpies of melting and vaporization for pure components

A mathematical model of the melting and vaporization enthalpies of organic components based on the theory of thermodynamic similarity is proposed. In this empirical model, the phase transition enthalpy for the homological series of n-alkanes, carboxylic acids, n-alcohols, glycols, and glycol ethers is presented as a function of the molecular mass, the number of carbon atoms in a molecule, and the normal transition temperature. The model also uses a critical or triple point temperature. It is shown that the results from predicting the melting and vaporization enthalpies enable the calculation of binary phase diagrams.     

Solution enthalpies of hydroxylic compounds

Solution enthalpies of adamantan-1-ol, 2-methyl- butan-2-ol, and 3-methylbutan-1-ol have been measured at 298.15 K, in a set of 16 protogenic and non-protogenic solvents. The identification and quantification of solvent effects on the solution processes under study were performed using quantitative-structure property relationships. The results are discussed in terms of solute–solvent–solvent interactions and also in terms of the influence of compound’s size and position of its hydroxyl group.     

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.     

Equilibrium melting points of the low-melting and high-melting crystalline forms of trans-1, 4-polyisoprene

Equilibrium melting points in trans-1,4-polyisoprene were calculated from plots of crystallization temperature versus the experimentally measured melting points. The melting points were found to be 78 ± 1.7°C for the low-melting crystalline form and 87 ± 1.3°C for the high-melting form. Within the experimental error, melting points were independent of molecular weight above a number-average weight of 33,000.     

Force field evaluation for biomolecular simulation: free enthalpies of solvation of polar and apolar compounds in various solvents.

Recently, the GROMOS biomolecular force field parameter set 53A6--which has been parametrized to reproduce experimentally determined free enthalpies of hydration and solvation in cyclohexane of amino acid side-chain analogs--was presented. To investigate the transferability of the new parameter set, we calculated free enthalpies of solvation of a range of polar and apolar compounds in different solvents (methanol, dimethyl sulfoxide (DMSO), acetonitrile, and acetone) from molecular dynamics simulations using the GROMOS 53A6 force field. For methanol and DMSO, parameters were used that are available in the 53A6 parameter set. For acetonitrile, a recently developed model was taken and for acetone, two models available in literature were used. We found that trends in and values for the solvation free enthalpies are in satisfactory agreement with experiment, except for the solvation in acetone for which deviations from experiment can be explained in terms of the properties of the models used.     

Standard enthalpies of formation of selected XYZ half-Heusler compounds

The standard enthalpies of formation of selected ternary half-Heusler type compositions XYZ (X = Au, Co, Fe, Ir, Ni, Pd, Pt, Rh, Ru; Y = Hf, Mn, Ti, Zr; Z = Ga, Sn) were measured using high temperature direct reaction calorimetry. The measured standard enthalpies of formation (in kJ/mole of atoms) of the half-Heusler compounds (prototype MgAgAs, Pearson symbol cF12, space group F-43m) are, IrMnSn (−29.4 ± 1.8); NiTiSn (−52.6 ± 2.4); PtHfSn (−98.8 ± 3.4); PtMnSn (−55.8 ± 2.6); PtTiSn (−93.6 ± 3.3); PtZrSn (−104.9 ± 3.8); for the B2 compound (prototype CsCl, Pearson symbol cP2, space group Pm-3m), RuMnGa (−26.9 ± 1.7); for the C1 structured (prototype CaF₂, Pearson symbol cF12, space group Pm-3m) or the C1_b structured compound IrMnGa (−40.9 ± 1.7). Indicative standard enthalpies of formation of the following compounds were obtained, half-Heusler compounds AuMnSn, CoTiSn, IrZrSn, NiHfSn, NiZrSn, PdHfSn, PdZrSn, RhTiSn; Heusler compound (prototype Cu₂MnAl, Pearson symbol cF16, space group Fm-3m) RhMnSn; hexagonal compound (prototype BeZrSi, Pearson symbol hP6, space group P6₃/mmc) PtMnGa and another type of hexagonal compound (prototype RhHfSn, Pearson symbol hP18, space group P-62c) RhHfSn, IrZrsn, RhZrSn. Values were compared with ab initio calculations from AFLOW and OQMD. Lattice parameters of these compounds were determined using X-ray diffraction (XRD) analysis. Microstructures were characterized using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Selected alloys were further annealed to investigate phase transformations and phase relationships.     

Parameters for calculation of standard enthalpies of formation of organic compounds in the liquid state

Conclusions A system of parameters for the calculation of standard enthalpies of formation of organic compounds has been developed. The system is based on group increments. It has been shown during the calculation of enthalpy of formation of polyfunctional compounds that in order to obtain accuracy close to the experimental value it is necessary to introduce corrections accounting for the interaction between the functional groups.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 372–375, February, 1986.     

Accurate prediction of enthalpies of formation for a large set of organic compounds

This article describes a multiparameter calibration model, which improves the accuracy of density functional theory (DFT) for the prediction of standard enthalpies of formation for a large set of organic compounds. The model applies atom based, bond based, electronic, and radical environmental correction terms to calibrate the calculated enthalpies of formation at B3LYP/6‐31G(d,p) level by a least‐square method. A diverse data set of 771 closed‐shell compounds and radicals is used to train the model. The leave‐one‐out cross validation squared correlation coefficient q² of 0.84 and squared correlation coefficient r² of 0.86 for the final model are obtained. The meanabsolute error in enthalpies of formation for the dataset is reduced from 4.9 kcal/mol before calibration to 2.1 kcal/mol after calibration. Five‐fold cross validation is also used to estimate the performance of the calibration model and similar results are obtained. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Calculations of the enthalpies of combustion of organic compounds by the additive scheme

The enthalpies of combustion of more than 200 organic compounds were analyzed. Group contributions to Δ_c H ^o were calculated and used to estimate the enthalpies of combustion of a wide range of organic substances of various classes.

     

Space-group multiplicities of polymorphs of inorganic compounds and lattice enthalpies

The relationships between lattice enthalpies (LEs) and multiplicities of points in general positions or orders of the point groups of the space groups have been studied for 71 inorganic compounds exhibiting at least two polymorphs. The LEs of the ionic crystals have been obtained through the Born–Haber (BH) thermochemical cycle, including halides, chalcogenides, oxohalides, and binary and complex oxides. It has been found for the range of LEs (600–39,000 kJ mol^?1) and relevant crystal structures that: (i) most of the polymorphs with higher multiplicities correspond to those stable under standard conditions compared to the lower-in-stability polymorphs and (ii) the products of multiplicity times order depend hyperbolically on the LE per unit symmetry point in general position.     

CORAL: QSPRs of enthalpies of formation of organometallic compounds

Available on the Internet the CORAL software gives reasonable good prediction for standard enthalpy of formation for selected organometallic compounds (n = 132). The approach is tested using five random splits of the considered data into the sub-training set (n = 32–49), calibration set (n = 36–51), test set (n = 10–29), and the validation set (n = 22–41). Compounds of the validation set are not involved in building up the models. The average statistical quality of prediction is the following: correlation coefficient ( $\overline{R^{2}} )$ R 2 ¯ ) $0.991\pm 0.005$ 0.991 ± 0.005 and standard error of estimation ( $\overline{s} )$ s ¯ ) $22.9 \pm 5.6$ 22.9 ± 5.6  kJ/mol.     

A simplified prediction of entropy of melting for energetic compounds

A new widely applicable model for the prediction of the entropy of melting of organic compounds is presented. The use of three simple geometry based parameters: rotational symmetry, flexibility, and eccentricity enables the simple and accurate prediction of this important property. This paper demonstrates the use of the model for energetic compounds.     

Measurement of enthalpies of vaporization of volatile heterocyclic compounds by DSC

An experimental procedure is proposed for direct measurement of the heat involved in the vaporization of volatile heterocyclic compounds. This technique consists on the vaporization of the liquid substance by a sudden decrease of the pressure then, the direct register of heat flow as function of time by differential scanning calorimetry. This procedure allows quantifying the enthalpy of vaporization of compounds such as tetrahydropyran, 2-methoxy-tetrahydropyran, N-morpholine and N-methyl-morpholine. Enthalpies of vaporization were measured in isothermal mode at T=298.15 K and then compared with results from the literature, which currently are obtained by vapour pressure measurements.     

The standard enthalpies of formation of nitro compounds with small rings

The energies of combustion and standard enthalpies of formation of 1-nitrospiro[2.3]hexane, 7-nitrodispiro[3.0.3.1]nonane, and 1,1-dinitrocyclopropane were determined experimentally.     

Molar enthalpies of formation of LnAl2 compounds

The enthalpy of solution of Eu in Al and the standard molar enthalpy of formation of LnAl₂ (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb) were determined by dissolution calorimetry, using a calorimeter based on liquid aluminium. Experimental results are compared with model predictions.     

Excess volumes and enthalpies of mixing benzene with various bicyclic compounds

The V _m ^E and H _m ^E for solutions of benzene in decahydronaphthalene, in bicyclohexyl, in cyclohexylbezene and in 1,2,3,4-tetrahydronaphthalene have been measured over the complete composition range at 25°C. The results have been fitted to the Flory theory of liquid mixtures.