Standard Enthalpies Of Vaporization Research Articles

Data-driven, explainable machine learning model for predicting volatile organic compounds’ standard vaporization enthalpy

The accurate prediction of standard vaporization enthalpy (ΔvapHm°) for volatile organic compounds (VOCs) is of paramount importance in environmental chemistry, industrial applications and regulatory compliance. To overcome traditional experimental methods for predicting ΔvapHm° of VOCs, machine learning (ML) models enable a high-throughput, cost-effective property estimation. But despite a rising momentum, existing ML algorithms still present limitations in prediction accuracy and broad chemical applications.In this work, we present a data driven, explainable supervised ML model to predict ΔvapHm° of VOCs. The model was built on an established experimental database of 2410 unique molecules and 223 VOCs categorized by chemical groups. Using supervised ML regression algorithms, the Random Forest successfully predicted VOCs' ΔvapHm° with a mean absolute error of 3.02 kJ mol−1 and a 95% test score. The model was successfully validated through the prediction of ΔvapHm° for a known database of VOCs and through molecular group hold-out tests. Through chemical feature importance analysis, this explainable model revealed that VOC polarizability, connectivity indexes and electrotopological state are key for the model's prediction accuracy. We thus present a replicable and explainable model, which can be further expanded towards the prediction of other thermodynamic properties of VOCs.

Density, vapor pressure, enthalpy of vaporization and heat capacity of (E)-isobutyl cinnamate

The density of (E)-isobutyl cinnamate at 297.95–535.20 K was measured using a capillary pycnometer and linearly related to temperature. The vapor pressure of (E)-isobutyl cinnamate at 420.15–570.05 K was measured by the ebulliometric method, and correlated by Antoine equation with an average relative deviation of 1.11 %. The vaporization enthalpy ΔvapH (Tb) of (E)-isobutyl cinnamate at normal boiling point was obtained based on the Clausius-Clapeyron equation. The standard vaporization enthalpy ΔvapH (298.15 K) was calculated to be 73.67±0.5 kJ·mol−1 by Othmer's method and verified by the Corresponding State Group Contribution (CSGC) method. The heat capacities at saturation vapor pressure (CSL) of (E)-isobutyl cinnamate were measured at 298.15–533.15 K by an automatic calorimeter and correlated by a quadratic polynomial.

Determination and Analysis of Thermodynamic Properties of Methyl Methylanthranilate Isomers.

The enthalpies of formation in the gaseous phase of methyl 3-methylanthranilate and methyl 5-methylanthranilate were determined from experimental measurements of the corresponding standard energies of combustion, obtained from combustion calorimetry, and the standard enthalpies of vaporization and sublimation, obtained from Calvet microcalorimetry and Knudsen mass-loss effusion. A computational study, using the G3(MP2)//B3LYP composite method, has also been performed for the calculation of the gas-phase standard enthalpies of formation of those two molecules at T = 298.15 K, as well as for the remaining isomers, methyl 4-methylanthranilate and methyl 6-methylanthranilate. The results have been used to evaluate and analyze the energetic effect of the methyl substituent in different positions of the ring.

Chemical Applicability of Second Order Sombor Index

In this paper, we introduce the higher-order Sombor index of a molecular graph. In addtition, we compute the second order Sombor index of some standard class of graphs and line graph of subdivision graph of 2D-lattice, nanotube and nanotorus of TUC_4C_8[p,q] and also we obtain the expressions of the second order Sombor index of the line graph of subdivision graph of tadpole graph, wheel graph, ladder graph and chain silicate network CSn. Further, we study the linear regression analysis of the second order Sombor index with the entropy, acentric factor, enthalpy of vaporization and standard enthalpy of vaporization of an octane isomers.

An investigation of edge F-index on fuzzy graphs and application in molecular chemistry

The molecular descriptors are a useful tool in the spectral graph, molecular chemistry and several fields of chemistry and mathematics. The edge F-index is proposed for fuzzy graphs (FGs) here. Bounds of this index are calculated for FGs. The FG has been investigated for a given set of vertices as having maximum edge F-index. Some relations of this index with the second Zagreb index and hyper-Zagreb index are established. For an isomorphic FGs, it is shown that the value of this index is the same. Bounds of this index for some FG operations are determined. Also, an application of the index in mathematical chemistry is studied. For this, 18 octane isomers and 67 alkanes are considered and analyzed the correlation between this index with some properties of the octane isomers and alkanes. From the correlation coefficient value, we have obtained this index is highly correlated with enthalpy of vaporization, standard enthalpy of vaporization, entropy, acentric factor and heat of vaporization and less correlated with heat capacity for octane isomers. Also, this index is correlated with critical pressure, critical temperature, molar refraction, molar volume and boiling point and is less correlated with surface tension and heat of vaporization for alkanes. But, this index is inadequate to determine the melting point of alkanes.

Sharp Bounds of First Zagreb Coindex for F -Sum Graphs

Let G = V E , E G be a connected graph with vertex set V G and edge set E G . For a graph G, the graphs S(G), R(G), Q(G), and T(G) are obtained by applying the four subdivisions related operations S, R, Q, and T, respectively. Further, for two connected graphs G 1 and G 2 , G 1 + F G 2 are F -sum graphs which are constructed with the help of Cartesian product of F G 1 and G 2 , where F ∈ S , R , Q , T . In this paper, we compute the lower and upper bounds for the first Zagreb coindex of these F -sum (S-sum, R-sum, Q-sum, and T-sum) graphs in the form of the first Zagreb indices and coincides of their basic graphs. At the end, we use linear regression modeling to find the best correlation among the obtained results for the thirteen physicochemical properties of the molecular structures such as boiling point, density, heat capacity at constant pressure, entropy, heat capacity at constant time, enthalpy of vaporization, acentric factor, standard enthalpy of vaporization, enthalpy of formation, octanol-water partition coefficient, standard enthalpy of formation, total surface area, and molar volume.

Measurement and correlation of the saturated vapor pressures of Ethenyltris(2,2,2-trifluoroethoxy)silane, Dimethoxymethyl(3,3,3-trifluoropropyl)silane and Trimethoxy(3,3,3-trifluoropropyl)silane

The saturated temperature of ethenyltris(2,2,2-trifluoroethoxy)silane (trisF-ES), dimethoxymethyl(3,3,3-trifluoropropyl)silane (F-DiMOMS) and trimethoxy(3,3,3-trifluoropropyl)silane (F-TriMOS) were determined using an inclined ebulliometer from 3.00 to 100.00 kPa. The experimental data were fitted with the Antoine equation and the Clarke−Glew equation by a weighted least-squares regression method, and gave the Antoine parameters (A = 8.8461, B = 1207.11, C = −114.06 K, A = 8.8040, B = 1166.06, C = −97.69 K and A = 8.9712, B = 1279.86, C = −92.77 K) and standard vaporization enthalpy ΔlgHm0(298.15 K) = 55.84 kJ mol−1, ΔlgHm0(298.15 K) = 47.54 kJ mol−1 and ΔlgHm0(298.15 K) = 49.48 kJ mol−1 for trisF-ES, F-DiMOMS and F-TriMOS, respectively. The critical properties of trisF-ES, F-DiMOMS and F-TriMOS, including critical temperature, pressure, and volume, were estimated by the group contribution method introduced by Nannoolal et al. The acentric factors (ω) of trisF-ES, F-DiMOMS and F-TriMOS were estimated from these critical parameters and the reduced saturated vapor pressures calculated using both the Antoine equation and the Clarke−Glew equation.

Synthesis and Thermodynamic Properties of Cadmium Oxopivalate CdPiv2 ∙ Cd4OPiv6

The cadmium oxopivalate complex CdPiv2 ∙ Cd4OPiv6 has been synthesized and its thermodynamic characteristics have been studied using the Knudsen effusion technique with the mass spectral analysis of the gas phase. It has been found that vaporization of this complex proceeds congruently and the saturated vapor above it consists of molecules Cd2Piv4, Cd4Piv8, and Cd4OPiv6. The standard enthalpies of sublimation of these molecules have been determined; the standard enthalpy of vaporization of complex CdPiv2 ∙ Cd4OPiv6 and standard enthalpy of dissociation of the Cd4Piv8 molecule according to the second and third laws of the thermodynamics have been found to be $${{\Delta }_{S}}H_{{298}}^{^\circ }$$ = 297.0 ± 12.1 kJ/mol and $${{\Delta }_{D}}H_{{298}}^{^\circ }$$ = 133.2 ± 16.8 kJ/mol, respectively. It is shown that the oxopivalate cadmium complex can be used as a precursor in the MO CVD method for the preparation of thin oxide films and coatings.

A norm indexes-based QSPR model for predicting the standard vaporization enthalpy and formation enthalpy of organic compounds

As important thermodynamic properties, vaporization enthalpy and formation enthalpy were extensively utilized in the chemical industry process and chemical engineering design, environment and agriculture. Based on the concept of norm index proposed by our group previously, a unified QSPR model was built for predicting four properties endpoints for 14 families of organic compounds. Four thermodynamic properties endpoints, including standard vaporization enthalpy (ΔHv0), standard formation enthalpy in gas state (ΔHf0(g)), standard formation enthalpy in solid state (ΔHf0(s)) and standard formation enthalpy in liquid state (ΔHf0(l)), were involved in the same modelling work. This model has satisfactory fitting effect for four properties endpoints with R2 of 0.967 for ΔHv0, R2 of 0.990 for ΔHf0(g), R2 of 0.989 for ΔHf0(s) and R2 of 0.987 for ΔHf0(l), respectively. Moreover, the results of internal validation, external validation and applicability domain analysis indicated the good stability and robustness of this model. This work not only calculated vaporization enthalpy and formation enthalpy with the same formula, but also covered gas, solid and liquid phases for formation enthalpy. Satisfying results obtained in the present work suggest that this model and norm indexes have good reliability and generalization.

Vaporization Thermodynamics of Polymeric Cadmium Pivalate

The vaporization of cadmium pivalate CdPiv2 with a polymeric structure was studied by the Knudsen effusion mass spectrometry of the gas phase. The sublimation of this complex was found to be congruent and to be accompanied by thermal dissociation with the formation of metal atoms and organic compounds due to its polymeric character. The standard enthalpies of vaporization were found, and the standard formation enthalpy of condensed cadmium pivalate was calculated. Highly volatile cadmium compounds could be synthesized via the introduction of additional ligands able to saturate the coordination sphere of the central atom.

Prediction of the Normal Boiling Points and Enthalpy of Vaporizations of Alcohols and Phenols Using Topological Indices

Establishing quantitative correlations between various molecular properties and chemical structures is of great technological importance for environmental and medical aspects. These approaches are referred to as Quantitative Structure-Property Relationships (QSPR), which relate the physico-chemical or thermodynamic properties of compounds to their structures. The main goal of QSPR studies is to find a mathematical relationship between the property of interest and a number of molecular descriptors derived from the structure of the molecule. The current study presents the relationship between the Randic′ (1χ), Balaban (J),Wiener polarity (Wp), Hyper Wiener (WW), Szeged (Sz), Harary (H) and Wiener (W) indices to the normal boiling points (Tbp, K) and the standard enthalpies of vaporization (ΔH vap 0 , kJ/mol–1) of 227 alcohols and phenols. The multiple linear regression (MLR) and backward methods were employed to give the QSPR models. After MLR analysis, we studied the validation of linearity between the molecular descriptors in the best models for used properties. The results have shown that three descriptors (W, 1χ, J) could be efficiently used for estimating the normal boiling points, and two descriptors (1χ, J) could be used for modeling and predicting the standard enthalpies of vaporization of considered compounds.

Thermodynamic properties of some biphenyls

Standard vaporization enthalpies of 4-nitrobiphenyl and 1, 1′- biphenyl are obtained on an isothermal heat conducting Calvet microcalorimeter with an estimated accuracy of ≤ 1 per cent for the first time. Standard formation enthalpies of some biphenyl derivatives in state of gas are determined. The calculation scheme by a method by “a double difference” of formation enthalpies of aromatic radicals and bond dissociation energies is offered. Using fundamental equations of the chemical physics, the new calculation method is offered to determine the energies of reorganization of molecules fragments into radicals. Formation enthalpies of radicals, namely biphenyl-4-yl and 3-methylfurazan-4-yl, are determined. Reorganization energies of radicals and bond chemical energies have been calculated.

Max-min Rodeg index of bridge graphs and fullerenes

Chemical graph theory is a branch of mathematical chemistry which deals with the nontrivial applications of graph theory to solve molecular problems. A graph-based molecular descriptors commonly known as topological indices describe the structures of chemical compounds. They are used in the isomer discrimination, structure property relationship, structure activity relations. Also, the certain physicochemical properties such as boiling point, enthalpy of vaporization, stability, and so on are able to be predicted by this technique. Molecules and molecular compounds are often modeled by molecular graph which is a representation of the structural formula of a chemical compound in terms of graph theory. Recently, the Max-min rodeg index (Mm sde ) which is vertex degree-based topological index has attracted attention and gained popularity. This index give the best predictor for enthalpy of vaporization and standard enthalpy of vaporization in the set of octane isomers and also for log water activity coefficient in the set of polychlorobiphenyles. A fullerene graph is a cubic planar graph whose faces are pentagons and hexagons. In this study, the Max-min rodeg index of fullerenes and link of fullerenes is computed. Moreover, it is presented exact expressions for the Max-min rodeg index of bridge graphs.

Energetic vs structural effects of aminoalkyl substituents in the morpholine

Abstract Experimental and computational studies were performed in this work with the aim of evaluating and understanding the energetic effect inherent to the substitution of the hydrogen of the morpholine amino group by aminoalkyl substituents: N -(2-aminoethyl)morpholine and N -(3-aminopropyl)morpholine. The standard enthalpies of vaporization and the standard energies of combustion of the two morpholine derivatives obtained, respectively, from Calvet microcalorimetry and combustion calorimetry measurements, are reported. These data were used to derive the standard enthalpies of formation of the morpholine derivatives, in the liquid and gaseous phases, at T = 298.15 K. The computational study involved the energetic analysis of the most stable conformers on the potential energy surfaces and the determination of their gas-phase standard enthalpies of formation at the reference temperature of 298.15 K. All the computational calculations were performed using the G3(MP2)//B3LYP composite method. The combination of experimental and computational data determined in this work for morpholine derivatives, together with other available in the literature for related molecules, enabled the analyses of the energetic effects associated with the substitution of the hydrogen of the morpholine amino group by substituents aminoalkyl and alkyl, as well as the establishment of incremental schemes for the determination of the gas-phase enthalpies of formation.

Vapor pressure and enthalpy of vaporization of trimethylolpropane and carboxylic acids esters

Vapor pressure and molar standard enthalpies of vaporization of esters of 2-ethyl-2-(hydroxymethyl)-1,3-propandiol (trimethylolpropane, TMP) and straight and branched carboxylic acids with chain length C1, C3-C6, were determinated by the transpiration method. A linear correlation of vaporization enthalpies of trimethylolpropane esters with the number of carbon atoms and with the Kovat's indices on the non-polar DB-1 GC column has been found. Enthalpies of vaporization of tested compounds were also calculated by QSPR-method. These results were checked by experimental values.

A New Tool for QSPR Researches: ev-degree Randić Index

Topological indices have important role in theoretical chemistry for QSPR researches. Among the all topological indices the Randić index has been used more considerably than any other topological indices in chemical and mathematical literature. Most of the topological indices as in the Randić index are based on the degrees of the vertices of a connected graph. Recently novel two degree concepts have been defined in graph theory; ev-degrees and ve-degrees. In this study ev-degree Randić index is defined by using ev-degree concept as parallel to their corresponding classical degree version. This new ev-degree Randić index is compared with the Randić index by modelling some physicochemical properties of octane isomers. It is showed that the ev-degree Randić index give better correlation than the Randić index to predict the entropy, acentric factor and standard enthalpy of vaporization of octanes. Also the exact values of the ev-degree Randić index for the well-known graph classes such as; paths, cycles, stars and complete graphs are given.

Calculation of Five Thermodynamic Molecular Descriptors by Means of a General Computer Algorithm Based on the Group-Additivity Method: Standard Enthalpies of Vaporization, Sublimation and Solvation, and Entropy of Fusion of Ordinary Organic Molecules and Total Phase-Change Entropy of Liquid Crystals.

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.

Measurement and Correlation Studies of the Saturated Vapor Pressure, Density, Refractive Indices, and Viscosity of Methyl 4-tert-Butylbenzoate

The saturated vapor pressure of methyl 4-tert-butylbenzoate was measured from (1.21 to 34.66) kPa in the temperature range from (398.3 to 492.4) K using a Swietoslawski-type ebulliometer. The experimental data were fitted with the Antoine and Clarke–Glew equations, which yielded Antoine parameters (A = 18.031, B = 7261.445, C = 8.857 K) and standard vaporization enthalpy (ΔlgHmθ (298.15 K) = 57.49 kJ mol–1), respectively. The critical properties were estimated on the basis of group contribution method. The acentric factor was calculated using these critical parameters and the saturated vapor pressures with the Antione equation. Furthermore, density, refractive indices, and viscosity of methyl 4-tert-butylbenzoate were also measured in the temperature range of 293.15 to 353.15 K. Temperature-dependence correlation equations for the density (second-order polynomial equation) and viscosity (Vogel–Tamman–Fulcher) were proposed. Modified Rackett equation was used with group contribution methods to predict the ...

Thermochemical properties of different 1-(R-phenyl)-1H-imidazoles

Phenyl substituted imidazoles exhibit versatile biological activity. 1-(R-phenyl)-1H-imidazoles with different functional groups R provide a convenient suitcase of molecules with tunable physicochemical properties adjustable for many practical applications. In this work, the absolute vapor pressures of 1-(R-phenyl)-1H-imidazoles (with R = H, 2-methyl, 4-methyl, 2-methoxy, 4-methoxy, 2-fluoro, 4-fluoro, 2-bromo and 4-bromo) at different temperatures have been measured by the transpiration method for the first time. The standard enthalpies of vaporization of these compounds were derived from the temperature dependencies of the vapor pressures. An internal consistency of the standard vaporization enthalpies has been proven by comparison with vaporization enthalpies of parent species, as well as by a group contribution method. A system of group-additivity values is suggested for a quick assessment of vaporization enthalpies of different 1-(R-phenyl)-1H-imidazoles. Gas-phase standard molar enthalpies of formation of 1-(R-phenyl)-1H-imidazoles have been calculated using the high-level quantum-chemical method G3MP2. The combination of experimentally determined standard vaporization enthalpies with the G3MP2 results allows for the prediction of the liquid-phase standard enthalpies of formation for the studied compounds.

Measurement and Correlation of Saturated Vapor Pressure of Ethylphenyldimethoxysilane and Ethylphenyldiethoxysilane

The saturated temperatures of ethylphenyldimethoxysilane (EPDMOS) and ethylphenyldiethoxysilane (EPDEOS) were determined using an inclined ebulliometer from 2.035 to 64.0 kPa. The experimental data were fitted with the Antoine and Clarke–Glew equations by a weighted least-squares regression method, which yielded Antoine parameters (A = 9.1280, B = 1590.18, C = −100.39 K and A = 9.1049, B = 1678.64, C = −102.84 K) and standard vaporization enthalpies (ΔlgHm0(298.15 K) = 62.52 kJ·mol–1 and ΔlgHm0(298.15 K) = 65.19 kJ·mol–1) for EPDMOS and EPDEOS, respectively. The critical properties of EPDMOS and EPDEOS, such as critical temperature, pressure, and volume, were estimated by the group contribution method introduced by Nannoolal et al. The acentric factors of EPDMOS and EPDEOS were estimated from these critical parameters and the reduced saturated vapor pressures calculated from either the Clarke–Glew equation or the Antoine equation.