Thermodynamic Estimate of pKa Values of the Carboxylic Acids in Aqueous Solution with the Density Functional Theory

The 96 pK_a values of 85 carboxylic acids in aqueous solution were calculated with the density functional theory method at the level of B3LYP/6‐31+G(d,p) and the polarizable continuum model (PCM) was used to describe the solvent. In the calculations of pK_a values, the dissociation Gibbs free energies were directly calculated using carboxylic acid dissociation reactions in aqueous solution, i. e., no thermodynamic cycle was employed, which is different from the previous literatures. A highly significant correlation of R²=0.95 with a standard deviation (SD) of 0.36 between the experimental pK_a values and the calculated dissociation Gibbs free energies [ΔG(calc.)] was found. The slope of pK_a vs. (G(calc.)/(20303RT) is only 47.6% of the theoretically expected value, which implies that the ΔG(calc.) value from the theoretical calculation is larger than the actual one for all 85 carboxylic acids studied. Thus, by adding the 0.476 scaling‐factor into the slope, we can derive a reliably procedure that can reproduce the experimental pK_a values of carboxylic acids. The pK_a values furnished by this procedure are in good agreement with the experimental results for carboxylic acids in aqueous solution.     

Theoretical Investigation on the Absorption and Emission Properties of the Three Isomers of Bis（thiocyanato）（2,2^1-bipyridyl）platinum（ll）

This paper presents a Density Functional or Time Dependent Density Functional （DFT/TDDFT） study of the molecular and electronic structures, optical absorption and emission spectra of three linkage isomers： bis（isothiocyanato-S）（2,2^1-bipyridyl） platinum（II） （[Pt（SCN）2（bpy）]）, （isothiocyanato-S）（thiocyanato-N）-（2,2^1-bipy- ridyl） platinum（II） （[Pt（SCN）（NCS）（bpy）]）, and bis（thiocyanato-N）（2,2^1）-bipyridyl）platinum（II） （[Pt（NCS）2（bpy）]）, in which different coordination ligands based on the N- and S-coordination of the thiocyanato ligands control the luminescent color. The electronic structures were studied using the B3LYP functional. Optimized geometries Were compared to the experimentally observed structures. TDDFT calculation was carded out to investigate the excited singlet and triplet states. Calculations have been performed both in vacuo and in solvents, using a polarized continuum model （PCM） to account for solute-solvent interactions. Inclusion of the solvent led to a significant energy change, and as a consequence, the computed spectrum calculated in the presence of the solvent was in good agree- ment with the experimental determinations. The first two absorptions were found to originate from mixed plati- num-SCN （or NSC） to bipyridyl-n＊ transitions rather than pure metal-to-ligand-charge-transfer （MLCT） transitions, whereas the higher-energy bands arose from intraligand n→π＊ transitions. The stretching frequencies of C≡N have been calculated both in the ground and excited states, which are relative to the charge transition during the excitation. In addition, different sizes of basis sets were also discussed in this paper.     

DFT Study of Solvent Effects for Some Organic Molecules Using a Polarizable Continuum Model

Forty ionic molecules are studied by DFT (B3LYP, B3P86), MP4 with different basis sets using the PCM/UAHF model within the self-consistent reaction-field method to assess solvent effects. For these molecules, the solvation free energies (ΔG _sol) in water and the dipole moments in vacuoas well as in water are obtained. By comparing the calculated values of ΔG _sol with experimental values and molecular simulation results, it is found that the ΔG _sol values generated by the DFT method are in better agreement with experimental values. Moreover, especially for the B3LYP/6-31+G_∗ level, the results of both ΔG _sol and dipole moments are more accurate considering the lower computational cost. It can be noted that the dipole moments of solutes in water show some increase relative to those in vacuo.     

溶液中类锗烯H2GeClMgCl的结构与异构化反应

用密度泛函理论(DFF)和 QCISD (quadratic configuration interaction with single and double excitations)方法研究了类锗烯 H2CeCMgCl在气相和五种溶剂中的构型与异构化反应.结果表明,类锗烯 H2GeClMgCl有三种平衡构型.其中p-配合物型构型能量最低,是其存在的主要构型.讨论了溶剂效应对结构、能量与异构化反应的影响.计算模拟了最稳定构型的红外光谱.     

One-Pot Synthesis of 1,2,3-Triazoles using Polymer-Supported Propyne in Aqueous Solution

A practical and efficient liquid-phase synthesis of 1,2,3-triazoles using poly（ethylene glycol） as support in aqueous solution was described. The title compounds, 1,2,3-triazoles 5 were obtained by a one-pot three-component 1,3-dipolar cycloaddition reaction in middle yields. In addition, a series of unexpected products 7 of Sonogashira reaction were also formed under the same condition.     

DFT Study on the Origin of the Enantioselectivity of （S）-4-Hydroxylproline-Catalyzed Direct Aldol Reaction between Acetone and 4-Nitrobenzaldehyde

DFT-B3LYP calculations were carried out to study the enantioselectivity of the （S）-4-hydroxylproline-catalyzed direct aldol reaction between acetone and 4-nitrobenzaldehyde. Four transition structures associated with the stereo-controlling step of the reaction have been determined. They are corresponding to the anti and syn arrangements of the methylene moiety related to the carboxylic acid group in enamine intermediate and the si and re attacks to the aldehyde carbonyl carbon. The effect of DMSO solvent on the stereo-controlling step was investigated with polarized continuum model （PCM）. The computed energies of the transition states reveal the moderate enantioselectivity of the reaction.     

1-（4-硝基苯基）-3-（2-苯并咪唑）-三氮烯的合成及与铜（Ⅱ）的显色反应

报道了1-（4-硝基苯基）-3-（2-苯并咪唑）-三氮烯（NPBMT）的合成及其与铜（Ⅱ）的显色反应。在非离子表面活性剂OP存在下,于pH11．5的Na2B4O7-NaOH缓冲介质中,NPBMT与铜（Ⅱ）形成2：1的桔红色络合物,络合物的最大吸收峰为417nm,表观摩尔吸光系数为2．62×10^4 L·mol^-1·cm^-1,10mL溶液中,铜（Ⅱ）量在0—15μg／mL范围内符合比尔定律。该法用于人发和食品中微量铜的测定,测定结果与AAS法相符。     

New Heterocyclic Phosphorus Ylides: Synthesis,Crystal Structure,and Theoretical Calculation of Alkyl Substituted 3-(4-Benzoyl-1,5-diphenyl-2,3-dihydro-1H-pyrazol-3-yl)-3-oxo-2-(triphenylphosphoranylidene) Propanoates

Novel alkyl substituted 3-(4-benzoyl-1,5-diphenyl-2,3-dihydro-1H-pyrazol-3-yl)-3-oxo-2-(triphenylphosphoranylidene) propanoates (3) were synthesized from 4-benzoyl-1,5-diphenyl-1H-pyrazole-3-carbonylchloride (1) and alkyl (triphenylphosphoranylidene) acetates (2a–b). The synthesized compounds were characterized by elemental analysis, spectroscopic studies (3a–b), and single crystal X-ray diffraction (3a). The mechanism of the reaction between (1) and (2a) was studied by AM1, and the geometrical parameters of the studied molecules were also carried out in B3LYP methods with the standard 6–31G (d,p) basis set. NBO analysis were studied for 1 and 2a B3LYP methods with the standard 6–31G (d,p) basis set.     

Studies on the Oxazaborolidine-catalyzed Enantioselective Reduction of 3-Morpholin-4-yl-1-phenyl-1-propanone with Density Functional Theory

Density functional theory (DFT) has been applied to study the enantioselective reduction of 3-morpholin-4-yl-l-phenyl-l-propanone with borane catalyzed by (S)-4-benzyl-5,5-diphenyl-l,3,2-oxazaborolidine at the B3LYP/6-31G* level. All molecular species involved in the four reaction steps have been fully optimized and the structural parameters are provided, and the micro process of reaction was also investigated. The catalyst-alkoxyborane adduct formed in step Ⅲ exhibits a B-O-B-N tetra-atomic ring. Reaction coordination calculations show that BH3 can react with 3-morpholin-4-yl-l-phenyl-l-propanone spontaneously, resulting in the need of 2 tool BH3 in the reaction.     

Theoretical study on molecular structures, intramolecular proton transfer reaction, and solvent effects of 1-phenyl-3-methyl-4-(6-hydro-4-amino-5-sulfo-2,3-pyrazine)-pyrazole-5-one

The molecular structures and intramolecular proton transfer reaction of 1-phenyl-3-methyl-4-(6-hydro-4-amino-5-sulfo-2,3-pyrazine)-pyrazole-5-one have been investigated with both ab initio method and the density functional theory. The solvent effects are simulated using the self-consistent reaction field (SCRF) method within the framework of the polarizable continuum model (PCM). The results show that the computed geometrical parameters at the B3LYP levels are in better agreement with experimental values than those at the RHF levels, and the choice of functional in DFT plays an important role in describing the title compound. It is found that strong hydrogen bonds (O–H···N and O···H–N) exist in the title compound, and in the proton transfer process, the O–H bond is broken while the N–H bond is formed. In addition, the order of stability of the isomers remains the same in different solvents, while the barrier height of the proton transfer reaction and dipole moments for the title compound grow with the increase of the solvent polarity. Eventually, the NBO analysis shows that the strength of the hydrogen bond reduces with the increase of the solvent polarity.     

Insight into the Detailed Mechanism of HRh（CO）（PPh3）3 Catalyzed Hydroformylation of 1-Phenyl-1-（3-pyridyl）ethene：A DFT Study

Density functional calculations have been used to study the mechanism of 1-phenyl-1-(3-pyridyl)ethene hydroformylation using rhodium catalyst.Our calculations reveal that the rate-determining step is the oxidative addition of hydrogen molecule and the preferred path is the one involving ts3ans for the lowest activation free-energy (ΔrGa),63.8 kJ/mol.This reaction is demonstrated to be strong exothermic by-96.6 kJ/mol of branched products and-98.2 kJ/mol of linear products.And the predominant product is the linear 3-phenyl-3-(3-pyridal)propanal (pr-ns) determined by both thermodynamics and kinetics.These results are in agreement with the practicality experimental studies.     

Molecular Structure and Conformational Composition of 1-[(Methylthio)methyl]-2-nitrobenzene (MTMNB): A Theoretical and Experimental Study

The conformational composition of gaseous MTMNB and the molecular structures of the rotational forms have been studied by electron diffraction at 130^∘C aided by results from ab initio and density functional theory calculations. The conformational potential energy surface has been investigated by using the B3LYP/6-31G(d,p) method. As a result, six minimum-energy conformers have been identified. Geometries of all conformers were optimized using MP2/6-31G(d,p), B3LYP/6-31G(d,p), and B3LYP/cc-pVTZ methods. These calculations resulted in accurate geometries, relative energies, and harmonic vibrational frequencies for all conformers. The B3LYP/cc-pVTZ energies were then used to calculate the Boltzmann distribution of conformers. The best fit of the electron diffraction data to calculated values was obtained for the six conformer model, in agreement with the theoretical predictions. Average parameter values (r_a in angstroms, angle α in degrees, and estimated total errors given in parentheses) weighted for the mixture of six conformers are r(C–C) = 1.507(5), r(C–C)_{ring, av} = 1.397(3), r(C–S)_av = 1.814(4), r(C–N) = 1.495(4), r(N–O)_av = 1.223(3), ∠(C–C–C)_ring = 116.0–122.5, ∠ C6–C4–C7 = 118.2(4), ∠ C–C–S = 113.6(6), ∠ C–S–C = 98.5(12), ∠ N–C–C4 = 121.9(3), ∠(O–N–C)_av = 116.8(3), ∠ O–N–O = 127.0(4). Torsional angles could not be refined. Theoretical B3LYP/cc-pVTZ torsional angles for the rotation about C–N bond, φ_C−N, were found to be 30.5–36.5^∘ for different conformers. As to internal rotation about C–C and C–S bonds, values of φ_C−C = 68–118^∘ and φ_C−S = 66–71^∘ were obtained for the three most stable conformers with gauche orientation with respect to these bonds. Some conclusions of this work were presented in a short communication in Russ. J. Phys. Chem. 2005, 79, 1701.     

A Theoretical Study on the Stereoisomerism in the Complex of Cucurbit[8]uril with 2,6-Bis(4,5-dihydro-1H-imidazol-2-yl)naphthalene

Cucurbit[n]urils (CB [n]),macropolycyclic compounds self-assembled from an acid-catalyzed condensation of glycoluril and formaldehyde1, can form inclusion complexes with a number of organic substrates in water2. Usually, CB [6] is used in the studies because of its easy synthesis, and the driving forces for its binding are considered to be the hydrophobic effect and dipole-dipole interactions. CB[n] 1Very recently, Kim et al reported the synthesis of CB [5], CB [7], and CB [8]3. They fou…     

Theoretical study on the geometry and vibration of 1-[6-(4-Chlorophenyl)-1-[(6-chloropyridin-3-yl)methyl]-2-[(6-chloropyridin-3-yl)methylsulfanyl]-4-methyl-1,6-dihydropyrimidin-5-yl]ethanone

The solid phase FT-IR and FT-Raman spectra of 1-[6-(4-chlorophenyl)-1-[(6-chloropyridin-3-yl)methyl]-2-[(6-chloropyridin-3-yl)methylsulfanyl]-4-methyl-1,6-dihydropyrimidin-5-yl]ethanone (C25H21Cl3N4OS) were recorded in the region 4000-400 and 3500-100cm(-1), respectively. The vibrational spectra have been computed using density functional theory (B3LYP) and ab initio molecular orbital calculation (HF) with 6-31G(d, p) basis sets. A close agreement was achieved between the observed and calculated frequency by employing normal coordinate calculations. The observed and simulated spectra were found to be well comparable.     

1－甲氧基－1－锂乙烯的结构及其分解反应的DFT研究

用量子化学中的密度泛函DFT方法，在B3LYP／631G（d,p）水平上研究了－甲 氧基－1－锂乙烯的结构。结果表明，1－甲氧基－1－锂乙烯有4种平衡结构，其中 只有1种是稳定的。对稳定的平衡结构，找到了分解反应的过渡态。在得到分解反 应过渡态的基础上，根据Eyring过渡态理论，计算了不同温度下1-甲氧基－1-钾乙 烯分解反应的速率常数，并根据速率常数计算了其平均寿命τ，根据平均寿命τ讨 论这类物质的稳定性问题。     

Oxidizing Reactions of Azines. 7. Imination of 4-Aryl-1,2,3,6-tetrahydropyridines by Arylamines in the Presence of Potassium Permanganate. Molecular Structure of 1-Methyl-2-(4-nitrophenylimino)-4-phenyl-1,2,5,6-tetrahydropyridine

On treating 4-aryl substituted 1-methyl-1,2,3,6-tetrahydropyridines with potassium permanganate in the presence of arylamines a previously unknown intermolecular oxidative imination reaction occurs leading to the formation of 2-(arylimino)-1,2,5,6-tetrahydropyridines. The molecular structure of 1-methyl-2-(4-nitrophenylimino)-4-phenyl-1,2,5,6-tetrahydropyridine was studied by X-ray analysis and it was shown that the hydropyridine ring of the molecule has a sofa conformation and its amidine fragment is in the E-configuration.     

Mild and Efficient Synthesis of 1-（6-Chloroquinoxalin-2-yl）-2- [4-（trifluoromethyl）-2,6-dinitrophenyl] Hydrazine Derivatives by Microwave Irradiation

Some 1-（6-chloroquinoxalin-2-yl）-2-[4-（trifluoromethyl）-2,6-dinitrophenyl] hydrazine derivatives have been synthesized via both conventional and microwave assisted organic synthesis（MAOS） methods. The MAOS method is more effective on synthesizing these compounds than the conventional method in regard to the higher chemical yields of products（76%-98%） and the shorter reaction time（1-15 min）.     

Theoretical study on the hydrolysis mechanism of N,N-dimethyl-N'-(2-oxo-1, 2-dihydro-pyrimidinyl)formamidine: water-assisted mechanism and cluster-continuum model

The hydrolysis reaction of N,N-dimethyl-N'-(2-oxo-1, 2-dihydro-pyrimidinyl)formamidine (DMPFA), a model compound of the antivirus drug amidine-3TC (3TC = 2', 3'-dideoxy-3'-thiacytidine), is investigated by the hybrid density functional theory B3LYP/6-31+G (d,p) method. The hydrolysis reaction of the title compound is predicted to undergo via two pathways, each of which is a stepwise process. Path A is the addition of H2O to the C=N double bond in the amidine group to form a tetrahedral structure in its first step, and then the transfer of the H atom of hydroxyl leads to the corresponding products via four possible channels. Path B simultaneously involves the nucleophilic attack of H2O to the C atom of the C=N bond and the proton transfer to the N atom of amino group leading to the cleavage of the C-N single bond in the amidine group. The results indicate that path A is more favorable than path B in the gas phase. Moreover, to simulate the title reaction in aqueous solution, water-assisted mechanism and the cluster-continuum model, based on the SCRF/CPCM model, are taken into account in our work. The results indicate that it is rational for two water molecules served as a bridge to assist in the first step of path A and that cytosine rather than the cytosine-substituted formamide should be released from the tetrahedral intermediate via s six-membered cycle transition state (channel 2). Our calculations exhibit that the process toward the tetrahedral intermediate is the rate-determining step both in the gas phase and in aqueous solution.     

Structure and Dynamics of Angiotensin (1-7) Vasoactive Peptide in Aqueous Solution at the Density-Functional Based Tight-Binding Level

Summary : Structure and dynamics of heptapeptide Angiotensin (1-7) in aqueous solution have been investigated by means of density-functional based tight-binding molecular dynamics simulations. Solvent-solute interactions have been studied using a hybrid QM/MM method. The backbone of the heptapeptide remains relatively rigid in aqueous solution compared to gas phase. The solvent acts as a cushion, preventing the free motion of the molecule. Tyrosine is the residue which presents the smallest flexibility and the largest number of water molecules in its first solvation shell. This is in good agreement with the previously published NMR results. The intra– and intermolecular hydrogen bridges have been quantified and analyzed in terms of conformation and stability.