共查询到20条相似文献,搜索用时 15 毫秒
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Javad Jamali‐Paghaleh Ali Reza Harifi‐Mood Mohammad Reza Gholami 《Journal of Physical Organic Chemistry》2011,24(11):1095-1100
Aromatic nucleophilic substitution reaction of 1‐fluoro‐2,4‐dinitrobenzene with para‐substituted and meta‐substituted anilines was kinetically investigated in the mixtures of ethyl acetate and methanol at room temperature. The correlation of second‐order rate coefficients with Hammett's substituent constants yields a fairly linear straight line with negative slope in different mole fractions of ethyl acetate–methanol mixtures. The measured rate coefficients of the reaction demonstrated a dramatic variation in ethyl acetate–methanol mixtures with the increasing mole fraction of ethyl acetate. Linear free energy relationship (LFER) investigations confirm that polarity has a major effect on the reaction rate whereas the hydrogen‐bonding ability of the media has a slight effect on it. Nonlinear free energy relationship based on preferential solvation hypothesis showed differences between the microsphere solvation of the solute and the bulk composition of the solvents, and non‐ideal behavior is observed in the trend of the rate coefficients, which cover the LFER results. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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The free energy of a thermodynamic system is known to be a concave function of the temperature. This fact is used, together with some results due to Fisher, to deduce bounds on the internal energy of the two-dimensional Ising model, given reasonably accurate upper and lower bounds on the free energy. These free energy bounds are derived from renormalization group transformations. Unfortunately, the numerical accuracy of the bounds on the internal energy is poor. The reasons for the failure are discussed. 相似文献
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Igor A. Sedov Michail A. Stolov Boris N. Solomonov 《Journal of Physical Organic Chemistry》2011,24(11):1088-1094
An approach is suggested to describe the solvophobic effects in various solvents, qualitatively and quantitatively. We analyzed the relationships between the Gibbs energies and enthalpies of solvation of alkanes in various solvents on the basis of existing experimental data. It is shown that for a large group of solvents, there is a linear correlation between the two quantities. Other solvents, primarily self‐associated, show deviations from this line. These deviations are always positive, leading to a decrease in solubility, and can be used as a measure of the strength of the solvophobic effects. It is also shown that the solvophobic effects is not the only factor determining the solubility, even for alkane solutes. The magnitudes of contributions of the solvophobic effect into the Gibbs energies of solvation of various compounds in monohydric alcohols are determined. These magnitudes are found to be linearly correlated with a characteristic molecular volume of a solute. The slope of correlation grows up with the concentration of hydrogen bonds in the liquid solvent. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Nejeh Dhahri Boubaker Taoufik Régis Goumont 《Journal of Physical Organic Chemistry》2014,27(6):484-489
The rate constants of the reaction of p‐X‐substituted benzylidenemalononitriles 1a , 1b , 1c , 1d , 1e , 1f , 1g , 1h with hydroxide ion were measured in 50% water–50% acetonitrile at 20 °C. The experimental kinetic data reveal that the points pertaining to electron donating substituted compounds (X = Me, OMe and NMe2) exhibit negative deviations from the Hammett plot. However, the Yukawa–Tsuno plot for the same rate constants resulted in a good straight line with an excellent correlation coefficient (r2 = 0.9916) and an r value of 1.15. Possible ground‐state stabilization through resonance interactions has been suggested to explain the origin of the nonlinear Hammett plot. On the basis of the relationship between E and σp+, the electrophilicity parameter E of some benzylidenemalononitriles 1c and 1e , 1f , 1g , 1h has been evaluated. More importantly, the three compounds 1f (E = ?7.90), 1g (E = ?7.80) and 1h (E = ?7.55) exhibit high electrophilicities that compare well with that of 4,6‐dinitrobenzoselenadiazole (E = ?7.40), a compound which has a general behaviour representative for the superelectrophilic dimension. We have shown that the second‐order rate constants calculated from Mayr's approach for the reaction of 1a , 1b , 1c , 1d , 1e , 1f , 1g , 1h with hydroxide ion do not agree with the available experimental data. On the other hand, a good linear correlation between log kexp and log kcalc has been observed and discussed. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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Jacek M. Kowalski 《Journal of statistical physics》1977,16(2):197-200
It is proved that the free energy of a disordered system described by a quadratic form in Bose or Fermi operators with random coefficients, calculated in the simplest approximation for the associated eigenvalue problem, gives the upper (Bose case) and lower (Fermi case) bounds for the exact free energy. 相似文献
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王青 《原子与分子物理学报》2017,34(6)
氢键和极性相互作用在抑制剂-蛋白结合专一性识别过程中起到重要作用. 抑制剂Benzamidine(BEN)与胰岛素trypsin相互作用机制的阐明有助于胰岛素高效抑制剂的研发.本文采用分子动力学模拟和MM-PBSA(molecular mechanics-Poisson Boltzmann surface area)从原子层次上研究BEN与胰岛素的结合模式.结果表明抑制剂BEN的脒基不仅与Asp189的羰基产生静电相互作用,而且与残基Ser190和Gly214形成氢键相互作用.基于残基能量分解的计算表明抑制剂的苯基与残基His58, Cys191, Gln192, Trp211, Gly212和Cys215形成有利于抑制剂结合的疏水性相互作用.期望当前的研究能为胰岛素有效抑制剂的研发提供重要的理论指导. 相似文献
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氢键和极性相互作用在抑制剂-蛋白结合专一性识别过程中起到重要作用.抑制剂Benzamidine(BEN)与胰岛素trypsin相互作用机制的阐明有助于胰岛素高效抑制剂的研发.本文采用分子动力学模拟和MM-PBSA(molecular mechanics-Poisson Boltzmann surface area)从原子层次上研究BEN与胰岛素的结合模式.结果表明抑制剂BEN的脒基不仅与Asp189的羰基产生静电相互作用,而且与残基Ser190和Gly214形成氢键相互作用.基于残基能量分解的计算表明抑制剂的苯基与残基His58,Cys191,Gln192,Trp211,Gly212和Cys215形成有利于抑制剂结合的疏水性相互作用.期望当前的研究能为胰岛素有效抑制剂的研发提供重要的理论指导. 相似文献
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Gamal Abdel‐Nasser Gohar Sherine Nabil Khattab Omaima Osman Farahat Hosam Hassan Khalil 《Journal of Physical Organic Chemistry》2012,25(4):343-350
The reaction of the substituted phenacyl bromides 1a–e and 2a–e with thioglycolic acid 3 and thiophenol 6 in methanol underwent nucleophilic substitution SN2 mechanism to give the corresponding 2‐sulfanylacetic acid derivatives 4a–e, 5a–e and benzenethiol derivatives 9a–e, 10a–e. The reactants and products were identified by mass spectra, infrared and nuclear magnetic resonance. We measured the kinetics of these reactions conductometrically in methanol at a range of temperatures. The rates of the reactions were found to fit the Hammett equation and correlated with σ‐Hammett values. The ρ values for thioglycolic acid were 1.22–1.21 in the case of 4‐substituted phenacyl bromide 1a–e, while in the case of the nitro derivatives 2a–e they were 0.39–0.35. The ρ values for thiophenol were 0.97–0.83 in the case of 4‐substituted phenacyl bromide 1a–e, while in the case of the nitro derivatives 2a–e they were 0.79–0.74. The Brønsted‐type plot was linear with a α = ?0.41 ± 0.03. The kinetic data and structure‐reactivity relationships indicate that the reaction of 1a–e and 2a–e with thiol nucleophiles proceeds by a concerted mechanism. The plot of log k45 versus log k30, the plot log(kx,3‐NO2/kH) versus log(kx/kH), and the Brønsted‐type correlation indicate that the reactions of the thiol nucleophiles with the substituted phenacyl bromides 1a–e and 2a–e are attributed to the electronic nature of the substituents. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Farid Taherkhani Hadi Abroshan Hamed Akbarzadeh Alessandro Fortunelli 《Phase Transitions》2013,86(7):613-623
We investigate a one-dimensional (1-D) Ising model for finite-site systems. The finite-site free energy and the surface free energy are calculated via the transfer matrix method. We show that, at high magnetic fields, the surface free energy has an asymptotic limit. The absolute surface energy increases when the value of f (the ratio of magnetic field to nearest-neighbor interactions) increases, and for f?≥?10 approaches a constant value. For the values of f?≥?0.2, the finite-site free energy also increases, but slowly. The thermodynamic limit in which physical properties approach the bulk value is also explored. 相似文献
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AbstractDuring solid–solid precipitation, interface free energy anisotropy is known to drive faceting of precipitates. In this paper, using a recently developed phase field formulation based on higher order tensor terms, we develop and implement a family of phase field models and indicate the parameter choices which lead to faceted precipitate morphologies. We also indicate how to choose the parameters given either the known precipitate morphology or the interfacial free energy anisotropy. Specifically, we study the faceting of precipitates in systems with cubic and hexagonal anisotropies; in 2 and 3D implementation of our phase field model, the precipitates do show facets in accordance with the Wulff plot – including cases where the Wulff plot predicts facets made up of more than one family of planes. We also indicate the possible extensions of our model to study other problems of interest. 相似文献
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Surface free energy of non-stick coatings deposited using closed field unbalanced magnetron sputter ion plating 总被引:1,自引:0,他引:1
Chen-Cheng Sun Shyue-Bin Dai Shein-Long Tien Yaw-Shyan Fu 《Applied Surface Science》2007,253(8):4094-4098
Semiconductor IC packaging molding dies require wear resistance, corrosion resistance and non-sticking (with a low surface free energy). The molding releasing capability and performance are directly associated with the surface free energy between the coating and product material. The serious sticking problem reduces productivity and reliability. Depositing TiN, TiMoS, ZrN, CrC, CrN, NiCr, NiCrN, CrTiAlN and CrNiTiAlN coatings using closed field unbalanced magnetron sputter ion plating, and characterizing their surface free energy are the main object in developing a non-stick coating system for semiconductor IC molding tools. The contact angle of water, diiodomethane and ethylene glycol on the coated surfaces were measured at temperature in 20 °C using a Dataphysics OCA-20 contact angle analyzer. The surface free energy of the coatings and their components (dispersion and polar) were calculated using the Owens-Wendt geometric mean approach. The surface roughness was investigated by atomic force microscopy (AFM). The adhesion force of these coatings was measured using direct tensile pull-off test apparatus. The experimental results showed that NiCrN, CrN and NiCrTiAlN coatings outperformed TiN, ZrN, NiCr, CiTiAlN, CrC and TiMoS coatings in terms of non-sticking, and thus have the potential as working layers for injection molding industrial equipment, especially in semiconductor IC packaging molding applications. 相似文献
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Bartlomiej Kowalczyk Kyle J. M. Bishop Stoyan K. Smoukov Bartosz A. Grzybowski 《Journal of Physical Organic Chemistry》2009,22(9):897-902
Large and diverse databases of chemical reactions contain statistically significant information about the propensities of molecules to undergo specific chemical transformations. It is shown that this information can be quantified to reflect reaction thermodynamics/kinetics and can be used to construct primitive (yet accurate) reactivity indices from the counts of reported reactions involving molecules/molecular positions of interest. These indices correlate with frontier orbital (FO) populations or Hammett σ and ρ parameters for a range of reactions involving aromatic substrates. These findings suggest that large chemical databases are not only a historical repository of chemical knowledge but also tools with which one can make useful chemical predictions. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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We investigate the free energy relation for a system contacting with a non-Markovian heat bath and find that the validity of the relation sensitively depends on the non-Markovian memory effect, which is especially related to the initial preparation effect. This memory effect drives the statistical distribution of the system out of the initial preparation, even if the system starts from an equilibrium state. This leads to the violation of the free energy relation. A possible way of eliminating this memory effect is proposed. 相似文献
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Advancing and receding contact angles of water, formamide, glycerol and diiodomethane were measured on polypropylene (PP) and polycarbonate (PC) sample surfaces which solidified at Teflon, glass or stainless steel as matrix surfaces. Then from the contact angle hystereses (CAH) the apparent free energies of the surfaces were evaluated. The original PP surface is practically nonpolar, possessing small electron donor interaction (), as determined from the advancing contact angles of these liquids. It may result from impurities of the polymerization process. However, it increases up to 8-10 mJ/m2 for PP surfaces contacted with the solids. The PC surfaces both original and modified show practically the same . No electron acceptor interaction is found on the surfaces.The of modified PP and PC surfaces depend on the kind of probe liquid and contacted solid surface. The modified PP values determined from CAH of polar liquids are greater than that of original surface and they increase in the sequence: Teflon, glass, stainless steel surface, at which they solidified. No clear dependence is observed between and dielectric constant or dipole moment of the polar probe liquids. The changes in of the polymer surfaces are due to the polymer nature and changes in its surface structure caused by the structure and force field of the contacting solid. It has been confirmed by AFM images. 相似文献
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