Quantum Chemistry and Pharmacy: Diagnostic Check of the Thermochemistry of Ibuprofen.

The thermodynamic data on ibuprofen available in the literature shows that the disarray of experimental results is unacceptable for this very important drug. The data on ibuprofens available in the literature were collected, combined with our complementary experimental results and evaluated. The enthalpies of combustion and formation of the crystalline RS-(±)- and S-(+)-ibuprofens were measured using high-precision combustion calorimetry.

Experimental and computational thermochemistry: how strong is the intramolecular hydrogen bond in alkyl 2-hydroxybenzoates (salicylates).

Hydrogen bonding (HB) is a fascinating phenomenon that exhibits unusual properties in organic and biomolecules. The qualitative manifestation of hydrogen bonds is known in numerous chemical processes. However, quantifying HB strength is a challenging task, especially in the case of intra-molecular hydrogen bonds.

Dissecting intermolecular interactions in the condensed phase of ibuprofen and related compounds: the specific role and quantification of hydrogen bonding and dispersion forces.

Ibuprofen is a well-established non-steroidal anti-inflammatory drug, inhibiting the prostaglandin-endoperoxide synthase. One of the key features defining the ibuprofen structure is the doubly intermolecular O-HO[double bond, length as m-dash]C hydrogen bond in cyclic dimers as know from carboxylic acids and confirmed by X-ray analysis. Until now, there was neither information about the vaporization enthalpy of ibuprofen nor about how this thermal property is determined by the subtle balance between different types of intermolecular interaction.

Dissecting the Vaporization Enthalpies of Ionic Liquids by Exclusively Experimental Methods: Coulomb Interaction, Hydrogen Bonding, and Dispersion Forces.

The quantification of hydrogen bonding and dispersion energies from vaporization enthalpies is a great challenge. Dissecting interaction energies is particularly difficult for ionic liquids (ILs), for which the composition of the different types of interactions is known neither for the liquid nor for the gas phase. In this study, we demonstrate the existence of ion pairs in the gas phase and dissect the interaction energies exclusively from measured vaporization enthalpies of different alkylated protic ILs (PILs) and aprotic ILs (AILs) and the molecular analogues of their cations.

How much different are thermochemical properties of enantiomers and their racemates? Thermochemical properties of enantiopure and racemate of methyl- and butyl lactates.

This work is a contribution to the molecular understanding of the thermodynamic properties of the chiral compounds. A comprehensive thermochemical study of the liquid enantiopure and racemate pairs of optically active alkyl lactates has been performed. Vapor pressures of DL-(±)-, L-(-)-methyl-, and DL-(±)-, L-(-)-n-butyl esters of lactic acid were measured by the transpiration method.

Thermochemistry of Substituted Benzamides and Substituted Benzoic Acids: Like Tree, Like Fruit?

Structure-property analyses of thermodynamic properties in chemical families of R-substituted benzamides, R-substituted benzoic acids, as well as R-substituted benzenes have been performed. The general linear interrelations for the vaporization enthalpies and the gas-phase enthalpies of formation between the chemical families under study have been established. These linear correlations provide a simple method for prediction of thermodynamic properties for benzenes with various combination of R-group substituents on the benzene ring.

Thermodynamics of enzyme-catalyzed esterifications: II. Levulinic acid esterification with short-chain alcohols.

Levulinic acid was esterified with methanol, ethanol, and 1-butanol with the final goal to predict the maximum yield of these equilibrium-limited reactions as function of medium composition. In a first step, standard reaction data (standard Gibbs energy of reaction Δ g ) were determined from experimental formation properties. Unexpectedly, these Δ g values strongly deviated from data obtained with classical group contribution methods that are typically used if experimental standard data is not available.

The Relation between Vaporization Enthalpies and Viscosities: Eyring's Theory Applied to Selected Ionic Liquids.

Key properties for the use of ionic liquids as electrolytes in batteries are low viscosities, low vapor pressure and high vaporization enthalpies. Whereas the measurement of transport properties is well established, the determination of vaporization enthalpies of these extremely low volatile compounds is still a challenge. At a first glance both properties seem to describe different thermophysical phenomena.

Nearest-Neighbor and Non-Nearest-Neighbor Interactions between Substituents in the Benzene Ring. Experimental and Theoretical Study of Functionally Substituted Benzamides.

Standard molar enthalpies of formation of 2- and 4-hydroxybenzamides were measured by combustion calorimetry. Vapor pressures of benzamide and 2-hydroxybenzamide were derived by the transpiration method. Standard molar enthalpies of sublimation or vaporization of these compounds at 298 K were obtained from vapor pressure temperature dependence.

Thermodynamic Analysis of Isomerization Equilibria of Chlorotoluenes and Dichlorobenzenes in a Biphasic Reaction Systems Containing Highly Acidic Chloroaluminate Melts.

Thermodynamics and kinetics of the isomerization of chlorotoluenes and dichlorobenzene to the technically desired meta-isomers have been studied in the presence of highly acidic chloroaluminate melts with alkali metal and organic imidazolium cations. Enthalpies of four isomerization processes in reacting systems of chlorotoluenes and dichlorobenzene were obtained from temperature dependencies of the corresponding equilibrium constants in the liquid phase. Experimental reaction enthalpies, enthalpies of vaporization, and absolute vapor pressures of chlorotoluenes and dichlorobenzene have been used for the validation of quantum-chemical methods to predict thermodynamic functions of the four reactions under study successfully.

Carbonate based ionic liquid synthesis (CBILS®): thermodynamic analysis.

Within the last decade the Carbonate Based Ionic liquid Synthesis (CBILS®) has developed towards a widely applicable, greener and halogen free process for the industrial production of ionic liquids. A large number of diverse starting materials have been screened experimentally, to explore the structural limits of the core reaction step, which is the quaternization of nitrogen, phosphor or sulfur based nucleophiles with carbonic acid dialkyl or diaryl esters to the corresponding quaternary alkyl- or arylcarbonates. In order to overcome the large experimental effort of empirical screening, a practical method based on quantum-chemical calculation has been developed for an assessment of feasibility of chemical reactions.

Benchmark Thermodynamic Properties of Methyl- and Methoxybenzamides: Comprehensive Experimental and Theoretical Study.

The enthalpies of formation of 2-, 3-, and 4-CH-benzamide, as well as for 2-CHO-benzamide, were measured by using combustion calorimetry. Vapor pressures of the isomeric CH- and CHO-benzamides were measured by using the transpiration method. The enthalpies of sublimation/vaporization of these compounds at 298 K were obtained from temperature dependencies of vapor pressures.

Dispersion and Hydrogen Bonding Rule: Why the Vaporization Enthalpies of Aprotic Ionic Liquids Are Significantly Larger than those of Protic Ionic liquids.

It is well known that gas-phase experiments and computational methods point to the dominance of dispersion forces in the molecular association of hydrocarbons. Estimates or even quantification of these weak forces are complicated due to solvent effects in solution. The dissection of interaction energies and quantification of dispersion interactions is particularly challenging for polar systems such as ionic liquids (ILs) which are characterized by a subtle balance between Coulomb interactions, hydrogen bonding, and dispersion forces.

Thermodynamics of Imidazolium-Based Ionic Liquids Containing PF6 Anions.

Imidazolium-based ionic liquids (ILs) with PF6(-) anions are considered as low-cost solvents for separation processes, but they exhibit restricted thermal stabilities. Reliable measurements of vaporization thermodynamics by conventional methods have failed. In this work, we applied a quartz-crystal microbalance method to determine for the first time the absolute vapor pressures for the [Cnmim][PF6] family, with n = 2, 4, 6, 8, and 10, in the temperature range 403-461 K.

An Examination of the Phase Transition Thermodynamics of (S)- and (RS)-Naproxen as a Basis for the Design of Enantioselective Crystallization Processes.

A detailed experimental analysis of the phase transition thermodynamics of (S)-naproxen and (RS)-naproxen is reported. Vapor pressures were determined experimentally via the transpiration method. Sublimation enthalpies were obtained from the vapor pressures and from independent TGA measurements.

Benchmark Thermochemistry for Biologically Relevant Adenine and Cytosine. A Combined Experimental and Theoretical Study.

The thermochemical properties available in the literature for adenine and cytosine are in disarray. A new condensed phase standard (p° = 0.1 MPa) molar enthalpy of formation at T = 298.

Benchmark thermochemistry of N-methylaniline.

In this work, the standard molar enthalpy of formation in the gaseous state of highly pure N-methylaniline, Δ(f)H(m)°(g, 298.15 K) = 90.9 ± 2.

Thermochemistry of dihalogen-substituted benzenes: data evaluation using experimental and quantum chemical methods.

Temperature dependence of vapor pressures for 12 dihalogen-substituted benzenes (halogen = F, Cl, Br, I) was studied by the transpiration method, and molar vaporization or sublimation enthalpies were derived. These data together with results available in the literature were collected and checked for internal consistency using structure-property correlations. Gas-phase enthalpies of formation of dihalogen-substituted benzenes were calculated by using quantum-chemical methods.

Transfer hydrogenation as a redox process in nucleotides.

Using a combined theoretical and experimental strategy, the heats of hydrogenation of the nucleotide bases uracil, thymine, cytosine, adenine, and guanine have been determined. The most easily hydrogenated base is uracil, followed by thymine and cytosine. Comparison of these hydrogenation enthalpies with those of ketones and aldehydes derived from sugar models indicates the possibility of near-thermoneutral hydrogen transfer between uracil and the sugar phosphate backbone in oligonucleotides.

Volatile times for the very first ionic liquid: understanding the vapor pressures and enthalpies of vaporization of ethylammonium nitrate.

A hundred years ago, Paul Walden studied ethyl ammonium nitrate (EAN), which became the first widely known ionic liquid. Although EAN has been investigated extensively, some important issues still have not been addressed; they are now tackled in this communication. By combining experimental thermogravimetric analysis with time of flight mass spectrometry (TGA-ToF-MS) and transpiration method with theoretical methods, we clarify the volatilisation of EAN from ambient to elevated temperatures.

Chelyabinsk airburst, damage assessment, meteorite recovery, and characterization.

The asteroid impact near the Russian city of Chelyabinsk on 15 February 2013 was the largest airburst on Earth since the 1908 Tunguska event, causing a natural disaster in an area with a population exceeding one million. Because it occurred in an era with modern consumer electronics, field sensors, and laboratory techniques, unprecedented measurements were made of the impact event and the meteoroid that caused it. Here, we document the account of what happened, as understood now, using comprehensive data obtained from astronomy, planetary science, geophysics, meteorology, meteoritics, and cosmochemistry and from social science surveys.

Making sense of enthalpy of vaporization trends for ionic liquids: new experimental and simulation data show a simple linear relationship and help reconcile previous data.

Vaporization enthalpy of an ionic liquid (IL) is a key physical property for applications of ILs as thermofluids and also is useful in developing liquid state theories and validating intermolecular potential functions used in molecular modeling of these liquids. Compilation of the data for a homologous series of 1-alkyl-3-methylimidazolium bis(trifluoromethane-sulfonyl)imide ([C(n)mim][NTf2]) ILs has revealed an embarrassing disarray of literature results. New experimental data, based on the concurring results from quartz crystal microbalance, thermogravimetric analyses, and molecular dynamics simulation have revealed a clear linear dependence of IL vaporization enthalpies on the chain length of the alkyl group on the cation.

Thermochemistry of uracils. Experimental and computational enthalpies of formation of 5,6-dimethyl-, 1,3,5-trimethyl-, and 1,3,5,6-tetramethyluracils.

We describe in the current paper an experimental and computational study of three methylated uracils, in particular, the 5,6-dimethyl-, 1,3,5-trimethyl-, and 1,3,5,6-tetramethyl derivatives. The values of the standard (p(0) = 0.1 MPa) molar enthalpies of formation in the gas phase at T = 298.

An elegant access to formation and vaporization enthalpies of ionic liquids by indirect DSC experiment and "in silico" calculations.

We used DSC for determination of the reaction enthalpy of the synthesis of the ionic liquid [C(4)mim][Cl]. A combination of DSC and quantum chemical calculations presents a new, indirect way to study thermodynamics of ionic liquids. The new procedure was validated with two direct experimental measurements and MD simulations.