Thermochemistry of heteroatomic compounds

The enthalpies of solvation of four geometric isomers of 2,5-dimethyl-1-phenyl-1-thioxophosphorinan-4-one in chloroform, nitrobenzene, and methanol were calculated using the enthalpies of vaporization of the isomers determined by the modified Solomonov—Konovalov method from the enthalpies of solution of the compounds in CCl₄ andp-xylene and molar refractions. The enthalpies of formation (ΔH _f ^o) of the isomers in the condensed and gas phase were assessed in the framework of Benson's group additivity scheme by summing the ΔH _f ^o values for phosphacycloketone fragments obtained from molecular mechanics calculations with the contributions of the phenyl group and S atom attached to the P atom. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1533–1536, September, 2000.     

Thermochemistry of heteroatomic compounds

The enthalpies of vaporization of different classes three-coordinated arsenic compounds have been determined according to their enthalpies of solution in hexane and molar refraction. The enthalpies of solvation of cyclic and acyclic As(III)-derivatives in hexane, carbon tetrachloride,p-xylene and pyridine are obtained and discussed. Part 6, see Ref. [1].     

Algorithms for GPU‐based molecular dynamics simulations of complex fluids: Applications to water,mixtures, and liquid crystals

A custom code for molecular dynamics simulations has been designed to run on CUDA‐enabled NVIDIA graphics processing units (GPUs). The double‐precision code simulates multicomponent fluids, with intramolecular and intermolecular forces, coarse‐grained and atomistic models, holonomic constraints, Nosé–Hoover thermostats, and the generation of distribution functions. Algorithms to compute Lennard‐Jones and Gay‐Berne interactions, and the electrostatic force using Ewald summations, are discussed. A neighbor list is introduced to improve scaling with respect to system size. Three test systems are examined: SPC/E water; an n‐hexane/2‐propanol mixture; and a liquid crystal mesogen, 2‐(4‐butyloxyphenyl)‐5‐octyloxypyrimidine. Code performance is analyzed for each system. With one GPU, a 33–119 fold increase in performance is achieved compared with the serial code while the use of two GPUs leads to a 69–287 fold improvement and three GPUs yield a 101–377 fold speedup. © 2015 Wiley Periodicals, Inc.     

Thermochemistry of heteroatomic compounds 22. Enthalpies of combustion and formation of alkyl(aryl)arsines and arsenites in the condensed and gaseous phases

The enthalpies of combustion (ΔH _comb) of five primary, secondary, and tertiary alkyl(aryl)arsines in the condensed state were calculated using the equation ΔH _comb = −385.8–110.3N, where N is the number of bond-forming electrons. The dependence presented is used for the calculation of the enthalpies of combustion of full esters and amidoesters of arsinous acid of noncyclic and cyclic structures. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1042–1043, May, 2007.     

Corrosion inhibition and performance evaluation on 2,5‐diaryl‐1,3,4‐thiadiazole and its derivatives

Using electrochemical impedance spectroscopy (EIS) and scanning electronic microscopy (SEM), this paper evaluated the inhibition effect of four 2,5‐diaryl‐1,3,4‐thiadiazole and its derivatives named 2,5‐diphenly‐1,3,4‐thiadiazole (DPTD), 2,5‐di(2‐hydroxyphenly)‐1,3,4‐thiadiazole (2‐DHPTD), 2,5‐di(3‐hydroxyphenly)‐1,3,4‐thiadiazole (3‐DHPTD), and 2,5‐di(4‐hydroxyphenly)‐1,3,4‐thiadiazole (4‐DHPTD) on silver strip corrosion in 50 mg/l sulfur–ethanol solution under room temperature. The experiments indicated that the inhibition efficiency increased with increasing inhibitor concentrations, and the increasing order was (4‐DHPDT) > (3‐DHPDT) > (2‐DHPDT) > (DPDT). Quantum chemical calculation was applied to correlate inhibition performances with their electronic structural parameters of thiadiazole derivatives. Molecular dynamics simulations (DFT) were used to optimize the equilibrium configurations of the inhibitor molecules on the silver surface and to investigate the molecular structure effect on the corrosion inhibition efficiency. The efficiency order of the investigated inhibitors, which was obtained by experimental results, was verified by theoretical calculations. Contact angle (CA) analysis was also carried out, and finally confirmed the existence of the adsorbed film which prevailed in addition of thiadiazole derivatives. CA analysis indicated that the film of n‐DHPTD (n = 2,3,4) was hydrophilic, owing to two hydroxyl groups in their molecular. The adsorption of these compounds onto silver strip from 50 mg/l S‐ethanol system obeys Langmuir adsorption isotherm, and it belongs to mixed‐type adsorption mainly dominated by chemisorption. Copyright © 2016 John Wiley & Sons, Ltd.     

Thermochemistry of Amines: Experimental Standard Molar Enthalpies of Formation of N-Alkylated Piperidines

The standard molar enthalpies of formation _f H _m ^° (l) at the temperature T = 298.15 K were determined using combustion calorimetry for N-methylpiperidine (A), N-ethylpiperidine (B), N-propylpiperidine (C), N-butylpiperidine (D), N-cyclopentylpiperidine (E), N-cyclohexylpiperidine (F), and N-phenylpiperidine (G). The standard molar enthalpies of vaporization _l ^g H ^{m °} of these compounds were obtained from the temperature variation of the vapor pressure measured in a flow system. From these data the following standard molar enthalpies of formation in gaseous phase _f H _m ^° (g) were derived for: A –(61.39 ± 0.88); B –(88.1 ± 1.3); C –(105.81 ± 0.66); D –(126.2 ± 1.3); E ( –88.21 ± 0.75); F –(135.21 ± 0.94); G (70.3 ± 1.4) kJ · mol^–1. They are used to determine the strain enthalpies of the cyclic amines A–G. The N-alkylated piperidine rings have been found to be about strainless.     

Pulling Polymers on Energetically Disordered Surfaces: Molecular Dynamics Tests of Linear and Non‐linear Response

Equilibrium and non‐equilibrium molecular dynamics simulations of flexible polymer chains absorbed on heterogeneous surfaces are presented. The surfaces are flat but energetically disordered, consisting of a random mixture of weakly and more strongly absorbing sites (94 and 6%, respectively). For comparison, the two corresponding homogeneous surfaces are also simulated. This apparently weak energetic disorder can produce significant changes of the chain statistics, equilibrium dynamics, and non‐equilibrium response to a horizontal pulling force. On the disordered surfaces, the polymer–surface effective friction coefficient becomes strongly force‐dependent, as the dominant mode of motion changes from localized stick–slip events to smooth and continuous sliding. This is strongly reminiscent of the Schallamach model of rubber friction and the Maier–Göritz picture of the Payne effect in filled elastomers.

     

Thermochemistry of Heteroatomic Compounds X. The thermochemistry of solution and solvation of substituted alkylphosphonic derivatives

The enthalpies of vaporization of different classes of phosphorylated alcohols and amines were determined from their enthalpies of solution in hexane and carbon tetrachloride. The enthalpies of specific (hydrogen-bond) interaction with the solvents (chloroform and pyridine) of derivatives containing X-H groups (X=O or N) in the α-position to the P=O group were determined. The results were explained in terms of the spatial structure of such compounds. This revised version was published online in August 2006 with corrections to the Cover Date.     

Experimental Enthalpies of Formation and Strain of the Methylated 1-Amino-2-phenylethanes

The standard molar enthalpies of formation H _f ^00B0; (liq) at the temperature t = 298.15 K were determined using combustion calorimetry for N-methyl-3-methyl-3-phenyl-2-butaneamine 1a, N,N-dimethyl-3-methyl-3-phenyl-2-butaneamine 1b N-methyl-2,3-dimethyl-3-phenyl-2-butaneamine 2a, and N,N-dimethyl-2,3-dimethyl-3-phenyl-2-butaneamine 2b. The standard molar enthalpies of vaporization H _vap ^00B0; of these compounds were obtained from the temperature variation of the vapor pressure measured in a flow system. The following standard molar enthalpies of formation in gaseous phase H _f ^00B0; (g) are obtained from these data: for 1a – 10.9 ± 1.9; 1b – 3.6 ± 1.8; 1c – 26.6 ± 1.4, and 1d – 23.0 ± 1.8 kJ mol^–1. From the standard molar enthalpies of formation for gaseous compounds which are available in the literature, improved values for the increments of the Benson group addivitiy scheme of amines were calculated. They are used to determine the strain enthalpies of the amines 1 and 2 from this investigation.     

Thermodynamics of mixtures containing unsaturated hydrocarbons by quasichemical group contributions

The quasichemical group surface interaction method was tested for its ability to correlate and predict vapor-liquid equilibrium (VLE) and molar excess enthalpy (H ^E ) in binary systems 1-octyne-1-propanol, 1-nonyne-1-propanol, 1-nonyne-1-butanol, 1-butylcyclopentene-nonane, 1-butylcyclopentene-1-butanol and 3-ethylcyclopentene-1-butanol. All computations involve using the few sets of group parameters obtained for CHC/OH by a change of the number of H ^E experimental points and the minimization function. For alkylcyclopentene systems, acyclic C=C group parameter as well as those of cyclic C=C and special cyclopentene groups have been used. The results have been compared with those obtained previously by the Wilson and UNIFAC methods.Communicated at the Festsymposium celebrating Dr. Henry V. Kehiaian's 60^th birthday, Clermont-Ferrand, France, 17–18 May 1990     

Thermochemical study of aliphatic and phenyl-substituted geminal diacetates

The standard enthalpies of combustion _c H ^o of aliphatic diacetates1 and aromatic diacetates2 were measured calorimetrically. The enthalpies of vaporization _vap H ^o or sublimation _sub H ^o of1 and2 were obtained from the temperature function of the vapor pressure measured in a flow system. From _f H ^o(g) of1 and2 new values of group increments for the estimation of standard enthalpies of formation of these classes of compounds were derived. The geminal interaction energy between the geminal acyloxy groups shows no anomeric stabilization.Geminal Substituent Effects, Part 12, for part 11 see Ref. 7.     

Thermodynamics of vaporization of gallium trichloride

The unsaturated and saturated pressures of gallium trichloride vapor were measured by the static method with membrane-gauge manometers in wide pressure (0.2–760 Torr) and temperature (313–1071 K) intervals. Scanning calorimetry was used to determine the thermodynamic characteristics of GaCl₃ fusion. The thermodynamic characteristics were obtained for sublimation, fusion, vaporization, and association in the vapor of GaCl₃ molecules. The enthalpies of formation and the absolute entropies of GaCl₃ in the liquid and gaseous phases and Ga₂Cl₆ in the gaseous phase were calculated using literature data. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1266–1269, July, 2007.     

A thermal analysis study of Ibuprofen

Ibuprofen has been subjected to a TG/DTA study over the temperature range of 30 to 350°C in a flowing atmosphere of nitrogen. The heating rate and the flow rate were varied. The DTA shows a melting at around 80°C and boiling point range from 212 to 251°C depending upon the heating rate. The mass loss in the TG data confirms the evaporation of Ibuprofen between them.p. and the normalb.p. Evaporation is limited to the surface area, which is a constant in the crucible holding the sample. The DTG plot shows clearly a zero order process which is consistent with the process of evaporation. The enthalpy of vaporization (_vap H) calculated by Trouton's rule is found to be in the range of 42.7–46.1 kJ mol^–1. TheE _act for the zero order reaction is in the range of 81.8–87.0 kJ mol^–1 and is calculated by use of the derivative method. The value ofE _act is about twice that for H _vap in Ibuprofen and differs from other compounds, whereE _act H _vap . It is suggested that the Ibuprofen molecule is existing as a dimer in the liquid state and dissociates to a monomer in the vapor state.     

Thermochemical studies for determination of the molar enthalpy of formation of aniline derivatives

The standard (p ^o=0.1 MPa) molar enthalpies of combustion atT=298.15 K were measured by static bomb combustion calorimetry for liquidN,N-diethylaniline,N,N-dimethyl-m-toluidine,N,N-dimethyl-p-toluidine, andN-ethyl-m-toluidine. Vaporization enthalpies forN,N-dimethyl-m-toluidine andN-ethyl-m-toluidine were determined by correlation gas chromatography. Derived standard molar values of _f H _m ^o (g) at 298.15 K forN,N-diethylaniline (62.1±7.6);N,N-dimethyl-m-toluidine (72.6±7.3),N,N-dimentyl-p-toluidine (68.9±7.4),N-ethyl-m-toluidine (30.5±3.8 kJ· mol^–1) were obtained.     

Predictions of solvation and vaporization enthalpies. 1.n-alkane +n-alkane solutions

A simple method for the calculation of the enthalpy of solvation is presented and demonstrated for 35 n-alkane + n-alkane solutions at 25°C. There is a good agreement between the predicted and experimental values. The calculation was based on the separation of the solvation enthalpy into the cavity formation and solute-solvent interaction contributions. The former term was determined from the activation enthalpy of the solvent viscous flow and solute molar volume while the latter on the basis of the dispersion energy using van der Waals diameters for n-propyl group. The procedure was also successful in prediction of the vaporization enthalpy of C₅–C₁₇ n-alkanes.     

环糊精的理论计算

环糊精对超分子化学的发展具有重要意义,其特殊的物理和化学性质已经在实验和理论研究中受到广泛关注。本文对近10年来环糊精的理论计算发展情况进行了综述。重点概述了分子动力学模拟结合自由能计算方法在环糊精识别和自组装行为中的应用,最后展望了环糊精未来的理论计算发展方向。     

Non-iterative and exact method for constraining particles in a linear geometry

We present a practical numerical method for evaluating the Lagrange multipliers necessary for maintaining a constrained linear geometry of particles in dynamical simulations. The method involves no iterations and is limited in accuracy only by the numerical methods for solving small systems of linear equations. As a result of the non-iterative and exact (within numerical accuracy) nature of the procedure, there is no drift in the constrained geometry, and the method is therefore readily applied to molecular dynamics simulations of, for example, rigid linear molecules or materials of non-spherical grains. We illustrate the approach through implementation in the commonly used second-order velocity-explicit Verlet method. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 911-916, 2005