Enthalpies of formation of olefinic ethers by G3(MP2)//B3LYP calculations

The gas‐phase enthalpies of formation at 298.15 K of a number of acyclic and cyclic olefinic ethers (mainly α,β‐unsaturated ethers), together with those of a few cyclic mono‐ and dienes, have been estimated by G3(MP2)//B3LYP calculations. In most cases, the computational and experimental data (if available) are in good mutual agreement. Whenever significant deviations between the experimental and computational data were found, the experimental enthalpies of formation arise from a single data source, and it appears that small experimental errors are embedded therein. A marked error was found in the experimental enthalpy of formation of 2‐chloroethyl ethyl ether, used in this work as a reagent for estimation of the enthalpy of formation of 2‐chloroethyl vinyl ether by an isodesmic reaction. Moreover, significant errors were also found in the literature values for the computational (B3LYP/6‐311G**) enthalpies of formation of several Me‐substituted derivatives of methyl vinyl ether. The present computational method, besides providing acceptable enthalpies of formation for unsaturated ethers, was also found to give accurate Δ_fH(g) values for cyclic mono‐ and dienes. Thus, the G3(MP2)//B3LYP computational method proved to be a valuable tool for investigating the energetics of olefinic ethers and hydrocarbons. Copyright © 2008 John Wiley & Sons, Ltd.     

Enthalpies of formation and isomerization of cis‐ and trans‐decalin,and their oxa‐analogs by G3(MP2)//B3LYP calculations

G3(MP2)//B3LYP calculations have been carried out on trans‐ and cis‐decalin, and their mono‐, di‐, tri‐, and tetraoxa‐analogs. The main purpose of the work was to obtain enthalpies of formation for these compounds, and to study the relative stabilities of the cis–trans and positional isomers of the various (poly)oxadecalins. Comparison of the computational enthalpies of formation with the respective experimental ones, known only for the decalins and 1,3,5,7‐tetraoxadecalins, shows that in both cases the computational values are more negative than the experimental ones, the deviations being ?5 to ?7 kJ mol^?1 for the decalins and ?12 to ?17 kJ mol^?1 for the 1,3,5,7‐tetraoxadecalins. The respective computational enthalpies of cis–trans isomerization, however, are in excellent to satisfactory agreement with the experimental data. The cis–trans enthalpy differences vary from +11.0 kJ mol^?1 for decalin to ?15.4 kJ mol^?1 for 1,4,5,8‐tetraoxadecalin. Low relative enthalpy values were also calculated for the cis isomers of 1,8‐dioxadecalin (?3.7 kJ mol^?1), 1,3,6‐trioxadecalin (?4.6 kJ mol^?1), 1,3,8‐trioxadecalin (?9.7 kJ mol^?1), 1,4,5‐ trioxadecalin (?5.6 kJ mol^?1), 1,3,5,8‐tetraoxadecalin (?7.3 kJ mol^?1), and 1,3,6,8‐tetraoxadecalin (?14.5 kJ mol^?1). Copyright © 2009 John Wiley & Sons, Ltd.     

Proximity effects of oxygen atoms on the enthalpies of formation of simple diethers: a computational G3(MP2)//B3 study

The enthalpies of formation of a number of acyclic, straight‐chain ethers and diethers were determined by G3(MP2)//B3 calculations. The principal aim of the work was to study the magnitude of the O…O proximity effect on the enthalpy contents of diethers as a function of the distance (number of bonds) between the O atoms. 1,4‐Diethers and 1,5‐diethers were computed to be destabilized by ca. 4.5 (±0.5) and 3.2 (±0.4) kJ mol^?1, respectively, by the O…O proximity effect. The effect was calculated to be negligible in diethers with the O atoms in positions more remote than 1,5 from each other, whereas 1,3‐diethers (acetals) are stabilized by ca. 22 kJ mol^?1, likely on account of the anomeric effect. Calculations on simple monoethers show that the contributions to of CH₂ groups in the β and γ positions (relative to O) are reduced by ca. 0.8 and 0.3 kJ mol^?1, respectively, relative to those of CH₂ groups more remote from the O atom. The computational enthalpies of formation of the studied monoethers and diethers, both cyclic and acyclic, are generally in good agreement with experimental data, another important result of the present work. Copyright © 2008 John Wiley & Sons, Ltd.     

Conformations and enthalpies of formation of methylenecyclohexane, 1,4‐dimethylenecyclohexane,cyclohexanone, 4‐methylenecyclohexanone, 1,4‐cyclohexanedione,and their mono‐ and dioxa derivatives by G3(MP2)//B3LYP calculations

A computational study of the stable conformations and gas‐phase enthalpies of formation at 25 °C of the title compounds has been carried out by G3(MP2)//B3LYP calculations. The work stems from our early observations on the thermodynamic and NMR spectroscopic properties of 2‐methylenetetrahydropyran and related compounds suggesting a dominating chair conformation, with poor p–π overlap in the ? O? C?C moiety, for these compounds. Besides computational verification of the chair conformation of 2‐methylenetetrahydropyran, the work was extended to find out the stable conformations of a number of other related compounds and to evaluate the relative stabilities of the various conformers. Another important goal of the work was the estimation of the gas‐phase enthalpies of formation of the present compounds, for which such literature data are scarce. A significant error in the literature value of the enthalpy of formation of methylenecyclohexane was found. Finally, the relative enthalpy levels of the isomeric compounds of this work are discussed. The high thermodynamic stability of the compounds containing an ester functional group, ? O? C?O, relative to the stability of isomeric compounds with an ? O? C?C moiety in place of the ester function, is demonstrated. Copyright © 2009 John Wiley & Sons, Ltd.     

Substituent effects on the formation of sulfonyl cations from sulfonyl chlorides: comparisons of solvolysis kinetic data with calculated gas phase energies

Suitable theoretical methods are validated for organosulfur compounds using experimental data for gas phase enthalpies of formation, proton affinities (PA) and heterolytic bond dissociation enthalpies (HBDEs). From enthalpies of chloride anion transfers from neutral chlorides to acyl, sulfonyl or cumyl cations in the gas phase, it is calculated that (i) similar aromatic substituent effects are expected for heterolyses of acyl, sulfonyl and cumyl chlorides; (ii) HBDEs for loss of chloride increase by over 70 kcal mol^?1 from 4‐MeOC₆H₄COCl to SO₂Cl₂. Rate constants for solvolyses of 4‐Z‐substituted arenesulfonyl chlorides (Z = OMe, Me, H, Cl, NO₂) in 97% w/w 2,2,2‐trifluoroethanol (TFE)–water are reported. Substituent effects are smaller than observed for identical solvolyses of acyl and cumyl chlorides, and are much smaller than those predicted theoretically for gas phase unimolecular heterolysis (explained by variable amounts of nucleophilic solvent assistance). Copyright © 2007 John Wiley & Sons, Ltd.     

The enthalpies of dissociation of the N?O bonds in two quinoxaline derivatives

The present work reports the first experimental thermochemical study of mono‐N‐oxides derived from quinoxaline, namely, 3‐methoxycarbonyl‐2‐methyl‐quinoxaline N‐oxide and 3‐ethoxycarbonyl‐2‐methyl‐quinoxaline N‐oxide. The values of the enthalpies of formation, in the condensed state, and of the enthalpies of sublimation, derived from static bomb calorimetry and Calvet microcalorimetry measurements, respectively, are combined to derive the standard molar enthalpies of formation in the gaseous phase for these two compounds. From the latter values, the first and second N? O bond dissociation enthalpies for the corresponding di‐N‐oxides have been obtained. The gas‐phase experimental results are also compared with calculated data obtained with a density functional theory approach. Copyright © 2008 John Wiley & Sons, Ltd.     

Energetic and structural characterization of 2‐R‐3‐methylquinoxaline‐1,4‐dioxides (R = benzoyl or tert‐butoxycarbonyl): experimental and computational studies

The gaseous standard molar enthalpies of formation of two 2‐R‐3‐methylquinoxaline‐1,4‐dioxides (R = benzoyl or tert‐butoxycarbonyl), at T = 298.15 K, were derived using the values for the enthalpies of formation of the compounds in the condensed phase, measured by static bomb combustion calorimetry, and for the enthalpies of sublimation, measured by Knudsen effusion, using a quartz crystal oscillator. The three dimensional structure of 2‐tert‐butoxycarbonyl‐3‐methylquinoxaline‐1,4‐dioxide has been obtained by X‐ray crystallography showing that the two N? O bond lengths in this compound are identical. The experimentally determined geometry in the crystal is similar to that obtained in the gas‐phase after computations performed at the B3LYP/6‐311 + G(2d,2p) level of theory. The experimental and computational results reported allow to extend the discussion about the influence of the molecular structure on the dissociation enthalpy of the N? O bonds for quinoxaline 1,4‐dioxide derivatives. As found previously, similar N? O bond lengths in quinoxaline‐1,4‐dioxide compounds are not linked with N? O bonds having the same strength. Copyright © 2007 John Wiley & Sons, Ltd.     

Theoretical studies on atmospheric chemistry of HFE‐347mcc3: reactions with OH radicals and Cl atoms

Detailed theoretical investigation has been performed on the mechanism, kinetics and thermochemistry of the gas phase reactions of CF₃CF₂CF₂OCH₃ (HFE‐347mcc3) with OH radicals and Cl atoms using M06‐2X/6‐31 + G(d,p) level of theory. Reaction profiles are modeled including the formation of pre‐reactive and post‐reactive complexes at entrance and exit channels, respectively. Using group‐balanced isodesmic reactions, the standard enthalpies of formation for species are also reported. The calculated bond dissociation energy for C―H bond is in good agreement with previous data. The rate constants of the two reactions are determined for the first time in a wide temperature range of 250–1000 K. At 298 K, the calculated rate coefficients are in good agreement with the experimental results. The atmospheric life time of HFE‐347mcc3 is estimated to be 4.4 years. Copyright © 2014 John Wiley & Sons, Ltd.     

Amino,ammonio and aminioethenes: a theoretical study of their structure and energetics

We have performed high level ab initio quantum mechanical calculations for aminoethene and the three isomeric 1,1‐ (Z)‐ or (E)‐1,2‐diaminoethenes as well as their singly and doubly charged cations derived by loss of electrons and/or upon protonation. Gas phase molecular structures were computed at the MP2/6‐311 + G(3df,2p) level. Standard molar enthalpies of formation in the gas phase, at T = 298.15 K, were estimated using the G3 composite method and atomization, isodesmic and homodesmotic reactions. Other energetic parameters were also calculated at the G3 level: proton affinities, basicities and adiabatic ionization enthalpies. Theoretical and experimental data are compared. The reported experimental data refer only to aminoethene wherein the standard molar enthalpy of formation has a considerable uncertainty, although the molecular structure is well established. There are no such data, neither structural nor thermochemical, for any of the three isomeric diaminoethenes. Isoelectronic comparisons are made. For example, the diprotonated diaminoethenes are isoelectronic to isobutene and (Z)‐ and (E)‐butene, while the doubly ionized diaminoethenes are likewise related to trimethylenemethane and 1,3‐butadiene. Copyright © 2013 John Wiley & Sons, Ltd.     

Kinetics and thermochemistry of the unusual [2π + 2σ + 2σ]‐cycloaddition of quadricyclane with some dienophiles

Kinetic parameters of the unusual [2π + 2σ + 2σ]‐cycloaddition reactions of quadricyclane ( 1 ) with tetracyanoethylene ( 2 ), 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione ( 3 ), N‐phenylmaleimide ( 4 ), and diethyl azodicarboxylate ( 5 ) are determined experimentally. Additionally, the enthalpies of 1  +  2 reaction in 1,4‐dioxane solution (?236.6 ± 1.0 kJ mol^?1) and 1  +  3 reaction in toluene (?255.0 ± 2.8 kJ mol^?1) are determined calorimetrically and shown to be the largest in absolute magnitude among all known cycloaddition reactions involving these dienophiles. Solvent effect on the rate of 1 + 3 reaction in 11 solvents is studied and found to be moderate and similar to that of the conventional Diels‐Alder and ene reactions. The difference in the reaction rate constants of 1 with different dienophiles can be up to 9 orders of magnitude and is mainly caused by the difference in activation enthalpies. This difference is not correlated with the standard enthalpies of reactions and is likely the result of high sensitivity of the [2π + 2σ + 2σ] reaction rates to the energy of donor‐acceptor interactions between the reactants.     

Computational study on structures,thermochemical properties,and bond energies of disulfide oxygen (S–S–O)‐bridged CH3SSOH and CH3SS(=O)H and radicals

Cleavage of disulfide bonds is a common method used in linking peptides to proteins in biochemical reactions. The structures, internal rotor potentials, bond energies, and thermochemical properties (Δ_fH°, S°, and Cp(T)) of the S–S bridge molecules CH₃SSOH and CH₃SS(=O)H and the radicals CH₃SS?=O and C?H₂SSOH that correspond to H‐atom loss are determined by computational chemistry. Structure and thermochemical parameters (S° and Cp(T)) are determined using density functional Becke, three‐parameter, Lee–Yang–Parr (B3LYP)/6‐31++G (d, p), B3LYP/6‐311++G (3df, 2p). The enthalpies of formation for stable species are calculated using the total energies at B3LYP/6‐31++G (d, p), B3LYP/6‐311++G (3df, 2p), and the higher level composite CBS–QB3 levels with work reactions that are close to isodesmic in most cases. The enthalpies of formation for CH₃SSOH, CH₃SS(=O)H are ?38.3 and ?16.6 kcal mol^?1, respectively, where the difference is in enthalpy RSO–H versus RS(=O)–H bonding. The C–H bond energy of CH₃SSOH is 99.2 kcal mol^?1, and the O–H bond energy is weaker at 76.9 kcal mol^?1. Cleavage of the weak O–H bond in CH₃SSOH results in an electron rearrangement upon loss of the CH₃SSO–H hydrogen atom; the radical rearranges to form the more stable CH₃SS· = O radical structure. Cleavage of the C–H bond in CH₃SS(=O)H results in an unstable [CH₂SS(=O)H]* intermediate, which decomposes exothermically to lower energy CH₂ = S + HSO. The CH₃SS(=O)–H bond energy is quite weak at 54.8 kcal mol^?1 with the H–C bond estimated at between 91 and 98 kcal mol^?1. Disulfide bond energies for CH₃S–SOH and CH3S–S(=O)H are low: 67.1 and 39.2 kcal mol^?1. Copyright © 2011 John Wiley & Sons, Ltd.     

A computational perspective on the kinetics and thermochemistry of the gas phase reactions of 1, 1-dichlorodimethylether (DCDME) with OH radical at 298 K

Kinetics and thermochemistry of the gas phase reactions between CH₃OCHCl₂ (DCDME) and OH radical are investigated theoretically. The geometries and all the stationary points on the potential energy surface are calculated at BHandHLYP/6-311G(d,p) method. The energy information is further refined at CCSD(T)/6-311G(d,p) level of theory. Reaction profiles are modelled including the formation of two pre-reactive and post-complexes. The rate constants, which are evaluated by Canonical Transition State Theory (CTST) including tunnelling correction at 298 K, are in very good agreement with the available experimental data. The percentage contributions of both reaction channels are also reported at 298 K. The hydrogen abstraction reaction from the –CHCl₂ group is found to be dominant leading to the formation of CH₃OCCl₂ + H₂O. Using group-balanced isodesmic reactions, the standard enthalpies of formation for CH₃OCHCl₂, CH₃OCCl₂ and CH₂OCHCl₂ are also reported.     

New concept of organic homo‐rank compounds and its application in estimating enthalpy of formation of mono‐substituted alkanes

Based on the topological characteristics of distance matrices and adjacency matrices of molecular graphs, a new concept of organic homo‐rank compounds was proposed. Based on this concept, compounds can be classified into new groups other than the traditional homologues. Furthermore, novel structure–property relationship approach named as homo‐rank compounds method can be developed. The feasibility of homo‐rank compounds method was explored by estimating the enthalpy of formation of organic compounds. The group contribution index (GCI_X) and group polarizability potential index (GPI_X) of substituents X were defined and determined for mono‐substituted alkanes RX (X includes 20 substituents). The research results show that the enthalpies of formation of organic homo‐rank compounds and their isomers can be correlated very well with the parameters GCI_X and GPI_X. Combining the method of homologues with that of homo‐rank compounds, a general and simple quantitative correlation equation (8) was established to estimate the enthalpy of formation for RX, and the calculation precision is within the chemical accuracy ‘1 kcal/mol’. For 242 samples of RX, the average absolute deviation between the experimental and the calculated values is 2.42 kJ/mol. In addition, the enthalpies of formation of more than 2800 samples of RX were estimated. The approaches of organic homo‐rank compounds and organic homologues are independent of but complementary to each other. The combination of these two methods can help us to understand the organic molecular structure–property relationships more deeply, and to investigate these relationships more conveniently and accurately. Copyright © 2015 John Wiley & Sons, Ltd.     

Computational study of the proton affinity and basicity of structurally diverse α1‐adrenoceptor ligands

The α₁‐adrenoceptor is a target for the treatment of several conditions from hypertension to benign prostatic hyperplasia. In this paper, we describe a new analysis approach to explore the conformational space of several ligands of the α₁‐adrenoceptor and we also present the calculation of their proton affinity and basicity. For each compound a conformational search followed by a semi‐empirical optimisation was performed and a selection of conformations for each ligand was subjected to further optimisation using density functional theory methods. Different positions were explored to determine the favoured site of protonation, and then, the proton affinity (in the gas phase) and basicity (using the polarisable continuum model for the aqueous solution) were calculated for each of them. In addition, an alternative method using one explicit water molecule in combination with the polarisable continuum model for aqueous solvent was explored. Moreover, the acid dissociation constant (pK_a) in water of these 26 compounds was calculated because this is an important parameter for a ligand when binding to its receptor. The experimental pK_a values of six of these ligands and those of two compounds with a very low and a very large pK_a were used to validate the theoretical methodology. Copyright © 2011 John Wiley & Sons, Ltd.     

Computational study on the kinetics of OH initiated oxidation of methyl difluoroacetate (CF2HCOOCH3)

The kinetics of hydrogen atom abstraction reactions of methyl difluoroacetate (CF₂HCOOCH₃) by OH radical has been studied by quantum mechanical method. The geometry optimisation and frequency calculation of the titled compound was performed with density functional theory using hybrid meta density functional MPWB1K with 6-31+G(d,p) basis set. Transition states have been determined and intrinsic reaction coordinate (IRC) calculation has been performed to ascertain that the transition from reactants to products was smooth through the corresponding transition state. Energy values are refined by making single point energy calculation at G3B3 level of theory and an energy level diagram is constructed. The standard enthalpies of formation of reactants and other species formed during the reaction were calculated using isodesmic method. The rate constants are calculated using canonical transition state theory and the overall rate constant is determined to be 1.35×10^?13 cm³ molecule^?1 s^?1 at 298 K and 1 atmospheric pressure. Tunnelling has been taken into account in the determination of the rate constant because it plays a critical role at low temperature especially when transfer of hydrogen takes place. The calculated value is found to be in good agreement with the experimentally determined value of 1.48×10^?13 cm³ molecule^?1 s^?1.     

A high‐level theoretical study into the atmospheric phase hydration,bond dissociation enthalpies,and acidity of aldehydes

CBS‐Q//B3, G4(MP2), and G4 composite method calculations were used to estimate atmospheric phase standard state (298.15 K, 1 atm) free energies of hydration (Δ_hydrG°_(g)), hydration equilibrium constants (log K_hydr,(g)), bond dissociation enthalpies (BDEs), and enthalpies (Δ_dH°_(g)) and free energies (Δ_dG°_(g)) of aldehydic proton acid dissociation for various substituted aldehydes with electron withdrawing and electron releasing groups. Good quality log K_hydr,(g) correlations with the Swain–Lupton resonance effect parameters R and R⁺ were found, allowing extension of the model to predict log K_hydr,(g) values for 487 substituted aldehydes having available R‐values and 108 substituted aldehydes having available R⁺ values. Good correlations were also found between experimental aqueous phase hydration equilibrium constants (log K_hydr,(aq)) and summative R/R⁺ values for peripheral substituents on a range of carbonyl derivatives (aldehydes, ketones, esters, and amides), suggesting that the structure–reactivity modeling approach can be extended to include all possible combinations of R₁C(O)R₂ carbonyl substitution in both gas and aqueous systems. Computationally derived BDEs and Δ_dH°_(g)/Δ_dG°_(g) were in good agreement with the limited experimental and theoretical datasets. BDEs did not generally correlate with any of the Hammett substituent constants or Swain–Lupton parameters considered. Gas phase acidities exhibited high correlation coefficients with Hammett inductive substituent constants (σ_I) and field effect parameters (F), allowing these to be employed as surrogates for estimating the gas phase aldehydic proton acidities of a larger potential compound range. The resulting models will be of use in predicting the environmental behavior for a broad range of environmentally relevant compounds containing carbonyl functionalities. Copyright © 2016 John Wiley & Sons, Ltd.     

Kinetics,mechanism and thermodynamics of reactions of CH3NHNH2 with OOH

Reactions between CH₃NHNH₂ and OOH radical were studied using computational methods. The activation energies (E_a) and Gibbs free energies of activation (ΔG^#) were calculated at the MP2 and B3LYP levels of theory. The calculated activation energies of the hydrogen abstraction reactions were less than 100 kJ/mol and those for the substitution reactions were about 150–250 kJ/mol. The calculated activation energies for the intra-molecular hydrogen transfer reactions in CH₃NHNH, CH₂NNH₂ and CH₃NN molecules were 210–250 kJ/mol. Catalytic effect of the water molecule on the intra-molecular hydrogen transfer reactions was studied. It was found that the water molecule decreases the activation energies by about 70–100 kJ/mol. Rate constants of the reactions were calculated using transition state theory in the temperature range of 298–2000 K. Consecutive hydrogen abstraction reactions from CH₃NHNH₂ led to the formation of CH₂NN, which was a very stable molecule.     

Structural and thermochemical studies on CH3SCH2CHO,CH3CH2SCHO,CH3SC(═O)CH3, and radicals corresponding to loss of H atom

CH₃SCH₂CHO, CH₃CH₂SCHO, and CH₃SC(═O)CH₃ are intermediates during the partial oxidation of CH₃SCH₂CH₃ in the atmosphere and in combustion processes. Thermochemical properties (ΔH_f^o, S^o and C_p(T)), structures, internal rotor potentials, and C─H bond dissociation energies of the parent molecules and their radicals formed after loss of a hydrogen atom are of value in understanding the oxidation processes of methyl ethyl sulfide. The lowest energy molecular structures were initially determined using the density functional B3LYP/6‐311G/(2d,d,p) level of theory. Standard enthalpies of formation (ΔH_f^o₂₉₈) for the radicals and their parent molecules were calculated using the density functional B3LYP/6‐31G(d,p), B3LYP/6‐31 + G(2d,p), and the composite CBS‐QB3 ab initio methods using isodesmic reactions. Internal rotation potential energy diagrams and internal rotation barriers were investigated using B3LYP/6‐31 + G(d,p) level calculations. The contributions for S^o₂₉₈ and C_p(T) were calculated using the rigid rotor harmonic oscillator approximation on the basis of the structures and vibrational frequencies obtained by the density functional calculations, with contributions from torsion frequencies replaced by internal rotor contributions from the method of Pitzer‐Gwinn. The recommended values for enthalpies of formation of the most stable conformers of CH₃SCH₂CHO, CH₃CH₂SCHO, and CH₃SC(═O)CH₃ are ?34.6 ± 0.8, ?42.4 ± 1.2, and ‐49.7 ± 0.8 kcal/mol, respectively. The structural and thermochemical data presented for CH₃SCH₂CHO, CH₃CH₂SCHO, and CH₃SC(═O)CH₃ and their radicals are of value in understanding the mechanism and kinetics of methyl ethyl sulfide oxidation under varied temperatures and pressures. Group additivity values are developed for estimating properties of structurally similar, larger sulfur‐containing compounds.     

Kinetic study on the aromatic nucleophilic substitution reaction of 3,6‐dichloro‐1,2,4,5‐tetrazine by biothiols

The aromatic nucleophilic substitution reaction of 3,6‐dichloro‐1,2,4,5‐tetrazine (DCT) with a series of biothiols RSH: (cysteine, homocysteine, cysteinyl–glycine, N‐acetylcysteine, and glutathione) is subjected to a kinetic investigation. The reactions are studied by following spectrophotometrically the disappearance of DCT at 370 nm. In the case of an excess of N‐acetylcysteine and glutathione, clean pseudo first‐order rate constants (k_obs1) are found. However, for cysteine, homocysteine and cysteinyl–glycine, two consecutive reactions are observed. The first one is the nucleophilic aromatic substitution of the chlorine by the sulfhydryl group of these biothiols (RSH) and the second one is the intramolecular and intermolecular nucleophilic aromatic substitutions of their alkylthio with the amine group of RSH to give the di‐substituted compound. Therefore, in these cases, two pseudo first‐order rate constants (k_obs1 and k_obs2, respectively) are found under biothiol excess. Plots of k_obs1 versus free thiol concentration at constant pH are linear, with the slope (k_N) independent of pH (from 6.8 to 7.4). The kinetic data analysis (Brønsted‐type plot and activation parameters) is consistent with an addition–elimination mechanism with the nucleophilic attack as the rate‐determining step. Copyright © 2014 John Wiley & Sons, Ltd.     

First-principles study on the structural,elastic, and thermodynamics properties of Ni3X (X: Al,Mo, Ti,Pt, Si,Nb, V,and Zr) intermetallic compounds

In the present study, the ground-state properties of Ni₃X intermetallic compounds were analyzed by means of the first-principles pseudo-potential method using the Cambridge serial total energy package code. The calculated lattice parameters of Ni₃X intermetallic compounds are in good agreement with the experimental and other theoretical data. The single-crystal elastic constants were calculated; the hardness, ductile, and plasticity of materials were analyzed. The calculated enthalpies of formation showed that all of intermetallic compounds were thermodynamically stable; Debye temperature and heat capacity are calculated and discussed. Moreover, the chemical bonding in these intermetallic compounds was interpreted by calculating the density of states, electron density difference distribution, and Mulliken analysis; magnetism properties were briefly analyzed.