1,2-二硫方酸的气相酸性和芳香性

在ＲＨＦ／６－３１１Ｇ、ＲＨＦ／６－３１１＋Ｇ　和Ｂ３ＬＹＰ／６－３１１＋Ｇ　水平,优化得到１,２－二硫方酸（３,４．二羟基－３－环丁烯－１,２－二硫酮）三种平面构象异构体的平衡几何构型．进一步用ＭＰＺ（ｆｕｌｌ）／６－３１１＋Ｇ　、／／ＲＨＦ／６－３１１＋Ｇ　方法计算三种异构体的单点能量,发现ＺＺ型异构体是能量最低构象,且ＺＺ和ＺＥ型能量非常接近．用优化的最稳定构象ＺＺ型异构体,在ＲＨＦ／６－３１１Ｇ　／／ＲＨＦ／６－３１１Ｇ　、ＲＨＦ／６．３１１＋Ｇ　／／ＲＨＦ／６－３１１＋Ｇ　、ＭＰＺ（ｆｕｌｌ）／６．３１１＋Ｇ　／／ＲＨＦ／６－３１１＋Ｇ　和Ｂ３ＬＹＰ／６－３１１＋Ｇ　斤Ｂ３ＬＹＰ／６－３１１＋Ｇ　水平,计算其气相酸性（△Ｇ＿２９８）,并用同键反应方法在同样水平计算其芳香性稳定化能．用基团加和法（ｇｒｏｕｐｉｎｃｒｅｍｅｎｔａｐｐｒｏａｃｈ）在ＲＨＦ／６．３１１＋Ｇ　／／ＲＨＦ／６－３１１＋Ｇ　和Ｂ３ＬＹＰ／６－３１１＋Ｇ　／／Ｂ３ＬＴｈ／６－３１１＋Ｇ　水平计算其磁化率增量（　）．计算结果指出,标题化合物的键长发生了平均化,芳香性稳定化能和磁化率增量均为负值,表明它具有芳香性,实现了标题化合物芳香     

3,4-二硫方酸芳香性和气相酸性的理论研究

在RHF/6-311G^**,RHF/6-311+G^**和B3LYP/6-311+G^**水平优化得到3,4-二硫方酸(3,4-二巯基-3-环丁烯-1,2-二酮)三种平面构象异构体的平衡几何构型.用MP2(Full)/6-311G^**//RHF/6-311G^**方法计算单点能量,发现ZZ型异构体是能量最低构象,且ZZ和ZE型能量非常接近.用优化的最稳定构象ZZ型异构体在RHF/6-311G^**//RHF/6-311G^**,RHF/6-311G^**//RHF/6-311G^**,MP2(Full)/6-311G^**//RHF/6-311G^**和B3LYP/6-311G^**//B3LYP/6-311G^**水平计算其气相酸性(ΔG⁰)和同键反应芳香性稳定化能(HASE).用基团加和法(Group Increment Approach)在RHF/6-311G^**//RHF/6-311G^**和B3LYP/6-311G^**//B3LYP/6-311G^**水平计算其磁化率增量(Λ).计算结果表明,标题化合物的同键反应芳香性稳定化能和磁化率增量均为负值,表明它具有芳香性,实现了标题化合物芳香性的几何、能量和磁性的判定.     

Gas-phase acidity of D-glucose. A density functional theory study

The gas-phase acidity of D-glucopyranose was studied by means of B3LYP calculations combined with 6-31G(d,p) or 6-31+G(d,p) standard basis sets. For each anomer, deprotonation of the various primary and secondary hydroxyl groups was considered. As in solution, the anomeric hydroxyl is found to be the most acidic for both anomers, but only when the 6-31+G(d,p) basis set is used for geometry optimization. Deprotonation of the anomeric hydroxyl induces an important C(1)--O endocyclic bond elongation and subsequently promotes an energetically favored ring-opening process as attested by the very small calculated activation barriers. The results also suggest that interconversion between the various deprotonated alpha- and beta-anomers may easily occur under slightly energetic conditions. B3LYP/6-311+G(2df,2p) calculations led to the an absolute gas-phase acidity of deltaacidGo(298)(alpha-D-glucose) = 1398 kJ mol(-1). This estimate matches well the only experimental value available to date. Finally, this study again confirms that the use of diffuse functions on heavy atoms is necessary to describe anionic systems properly and to achieve good relative and absolute gas-phase acidities.     

Theoretical predictions of the structure, gas-phase acidity and aromaticity of 1,2-diseleno-3,4-dithiosquaric acid

Results of ab initio self-consistent-field (SCF) and density functional theory (DFT) calculations of the gas-phase structure, acidity (free energy of deprotonation, ΔG^o), and aromaticity of 1,2-diseleno-3,4-dithiosquaric acid (3,4-dithiohydroxy-3-cyclobutene-1,2-diselenone, H₂C₄Se₂S₂) are reported. The global minimum found on the potential energy surface of 1,2-diseleno-3,4-dithiosquaric acid presents a planar conformation. The ZZ isomer was found to have the lowest energy among the three planar conformers and the ZZ and ZE isomers are very close in energy. The optimized geometric parameters exhibit a bond length equalization relative to reference compounds, cyclobutanediselenone, and cyclobutenedithiol. The computed aromatic stabilization energy (ASE) by homodesmotic reaction (Eq 1) is −20.1 kcal/mol (MP2(fu)/6-311+G** //RHF/6-311+G**) and −14.9 kcal/mol (B3LYP//6-311+G**//B3LYP/6-311+G**). The aromaticity of 1,2-diseleno-3,4-dithiosquaric acid is indicated by the calculated diamagnetic susceptibility exaltation (Λ) −17.91 (CSGT(IGAIM)-RHF/6-311+G**//RHF/6-311+G**) and −31.01 (CSGT(IGAIM)-B3LYP/6-311+G**//B3LYP/6-311+G**). Thus, 1,2-diseleno-3,4-dithiosquaric acid fulfils the geometric, energetic and magnetic criteria of aromaticity. The calculated theoretical gas-phase acidity is ΔG^o _1(298K)=302.7 kcal/mol and ΔG^o _2(298K)=388.4 kcal/mol. Hence, 1,2-diseleno-3,4-dithiosquaric acid is a stronger acid than squaric acid(3,4-dihydroxy-3-cyclobutene-1,2-dione, H₂C₄O₄). Received: 11 April 2000 / Accepted: 7 July 2000 / Published online: 27 September 2000     

2-溴丙酸气相热消除反应的机理

用密度泛函（DFT）方法,在B3LYP/6-31G**水平上对2-溴丙酸气相消除反应机理进行了研究.计算表明,反应主要是通过半极化五元环结构过渡态进行的,羧基上的氢原子协助溴原子离去,羧基氧原子帮助稳定过渡态.在B3LYP/6-311＋＋G(3df,3pd)水平上对B3LYP/6-31G**优化的几何构型进行了单点能计算,计算所得反应的速度控制步骤的活化能为189.461 kJ•mol－1,偏离实验值((180.3±3.4) kJ•mol－1)5.08％.     

3,4-二硒方酸芳香性和气相酸性的理论研究

在ＲＨＦ／６－３１１Ｇ水平优化得到３,４－二硒方酸（３,４－二氢硒基－３－环丁烯－１,２－二酮）３ 种平面构象异构体的平衡几何构型。进一步用ＭＰ２（ｆｕｌｌ）／６－３１１Ｇ／／ＲＨＦ／／６－３１１Ｇ方法计算单点能量,发现ＺＺ型异构体是能量最低构象,且ＺＺ和ＺＥ型能量非常接近。用优化的最稳定构象ＺＺ型异构体在ＲＨＦ／６－３１１Ｇ／／ＲＨＦ／６－３１１Ｇ、ＲＨＦ／６－３１１＋ Ｇ／／ＲＨＦ／６－３１１＋ Ｇ、ＭＰ２（ｆｕｌｌ）／６－３１１＋ Ｇ／／ＲＨＦ／６－３１１＋ Ｇ 和Ｂ３ＬＹＰ／６－３１１＋ Ｇ／／Ｂ３ＬＹＰ／６－３１１＋ Ｇ水平计算其气相酸性（ΔＧ°）和同键反应芳香性稳定化能（ＨＡＳＥ）。用基团加和法（ｇｒｏｕｐ ｉｎｃｒｅｍ ｅｎｔ ａｐ－ｐｒｏａｃｈ ） 在 ＲＨＦ／６－３１１ ＋ Ｇ／／ＲＨＦ／６－３１１ ＋ Ｇ 和 Ｂ３ＬＹＰ／６－３１１ ＋ Ｇ／／Ｂ３ＬＹＰ／６－３１１＋ Ｇ水平计算其磁化率增量（Λ）。计算结果指出标题化合物的同键反应芳香性稳定化能和磁化率增量均为负值,表明它具有芳香性,实现了标题化合物芳香性的几何、能量和磁性的判定。     

Chemical reactivity of hypervalent silicon compounds: The local hard and soft acids and bases principle viewpoint

The silicon atom may increase its coordination number to values greater than four, to form pentacoordinated compounds. It has been observed experimentally that, in general, pentacoordinated compounds show greater reactivity than tetracoordinated compounds. In this work, density functional theory is used to calculate the global softness and the condensed softness of the silicon atom for SiH _n F_4−n and SiH _n F _5−n ¹⁻ . The values obtained show that the global and condensed softness are greater in the pentacoordinated compounds than in the tetracoordinated compounds, a result that explains the enhanced reactivity. If the results are analysed through a local version of the hard and soft acids and bases principle, it is possible to suggest that in nucleophilic substitution reactions, soft nucleophiles preferably react with SiH _n F _5−n ¹⁻ , and hard nucleophiles with SiH _n F_4−n .     

Ab initio and density functional theory studies of the structure,gas-phase acidity and aromaticity of tetraselenosquaric acid

Results of ab initio self-consistent-field (SCF) and density functional theory (DFT) calculations of the gas-phase structure,acidity (free energy of deprotonation,G0) and aro-maticity of tetraselenosquaric acid (3,4-diselenyl-3-cy-dobutene-1,2-diselenone,H2C4Se4) are reported.The global minimum found on the potential energy surface of tetraselenosquaric acid presents a planar conformation.The ZZ iso-mer was found to have the lowest energy among the three planar conformers and the ZZ and ZE isomers are very dose in energy.The optimized geometric parameters exhibit a bond length equalization relative to reference compounds,cyclobu-tanediselenone,and cydobutenediselenol.The computed aromatic stabilization energy (ASE) by homodesmotic reaction is -77.4 (MP2(fu)/6 - 311 G //RHF/6 - 311 G) and - 54.8 kJ/mol (B3LYP/6 - 311 G //B3LYP/6 -311 G).The aromaticity of tetraselenosquaric add is indicated by the calculated diamagnetic susceptibility exaltation (A) - 19.13 (CSGT(IGAEM) - RHF/6 - 311 G// RHF/6-     

Complexes of a bio-molecule and a C60 cage

C₆₀ is the most important fullerene cage and glycine is the simplest representative of a backbone unit of a protein. In this paper, the structures and the energies of glycine–C₆₀ complexes were calculated at the B3LYP/6-31G(d) level DFT. It was found that the binding of glycine to C₆₀ generated a slightly unstable complex via its amino nitrogen, a moderately unstable complex via its hydroxyl oxygen, and a very unstable complex via its carbonyl oxygen. This indicates that fullerene cages might be unable to form stable bindings to proteins via their amino nitrogen, hydroxyl oxygen and carbonyl oxygen active sites.     

1, 2-二硒方酸气相酸性和芳香性的理论研究

在RHF/6-311G^*^*水平优化得到1,2-二硒方酸(3,4-二羟基-3-环丁烯-1,2-二硒酮)三种平面构象异构体的平衡几何构型。进一步用MP2(full)/6-311G^*//RHF/6-311G^*^*方法计算三种异构体的单点能量,发现ZZ型异构体是能量最低构象,且ZZ和ZE型能量非常接近。用优化的最稳定构象ZZ型异构体在RHF/6-311G^*^*//RHF/6-311G^*^*,RHF/6-311+G^*^*//RHF/6-311+G^*^*,MP2(full)/6-311+G^*^*//RHF/6-311+G^*^*和B3LYP/6-311+G^*^*//B3LYP/6-311+G^*^*水平计算其气相酸性[ΔGⅲ~(~2~9~8~K~)]和同键反应芳香性稳定化能(HASE)。用基团加和法(groupincrementapproach)在RHF/6-311+G^*^*//RHF/6-311+G^*^*和B3LYP/6-311+G^*^*//B3LYP/6-311+G^*^*水平计算其磁化率增量(Λ)。计算结果指出标题化合物的键长发生了平均化,同键反应芳香性稳定化能和磁化率增量均为负值,表明它具有芳香性,实现了标题化合物芳香性的几何、能量和磁性的判定。     

Theoretical predictions of the structure,gas‐phase acidity,and aromaticity of tetrathiosquaric acid

Results of ab initio self‐consistent‐field and density functional theory calculations of the gas‐phase structure, acidity (free energy of deprotonation, ΔG⁰), and aromaticity of tetrathiosquaric acid (3,4‐dithiohydroxy‐3‐cyclobutene‐1,2‐dithione, H₂C₄S₄) are reported. The global minimum found on the potential energy surface of tetrathiosquaric acid presents a planar conformation. The ZZ isomer was found to have the lowest energy among the three planar conformers and the ZZ and ZE isomers are very close in energy. The optimized geometric parameters exhibit a bond length equalization relative to reference compounds, cyclobutanedithione, and cyclobutenedithiol. The computed aromatic stabilization energy by homodesmotic reaction is −18.4 (MP2(fu)/6‐311+G**//RHF/6‐311+G**) and −15.1 kcal/mol (B3LYP//6‐311+G**// B3LYP/6‐311+G**). The aromaticity of tetrathiosquaric acid is indicated by the calculated diamagnetic susceptibility exaltation (Λ) −11.77 (CSGT(IGAIM)‐RHF/6‐311+G**// RHF/6‐311+G**) and −18.08 (CSGT(IGAIM)‐B3LYP/6‐311+G**// B3LYP/6‐311+G**). Thus, tetrathiosquaric acid fulfils the geometric, energetic and magnetic criteria of aromaticity. The most reliable theoretical gas‐phase acidities are $\Delta G^{0}_{1(298\mathrm{K})}=303.7$ and $\Delta G^{0}_{2(298\mathrm{K})}=394.1$ kcal/mol. Hence, tetrathiosquaric acid is a stronger acid than squaric acid (3,4‐dihydroxy‐3‐ cyclobutene‐1,2‐dione, H₂C₄O₄). Comparisons of the computed results of tetrathiosquaric acid with squaric acid have also been made. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 78: 443–449, 2000     

A new and efficient method for the facile synthesis of N-acyl sulfonamides under Lewis acid catalysis

The N-acylation of sulfonamides with carboxylic acid anhydrides in the presence of Lewis acids is described. Several Lewis acids such as BF₃·Et₂O, ZnCl₂, MoCl₅, TiCl₄, B(C₆F₅)₃, Sc(OTf)₃ and I₂ were found to catalyze the reaction efficiently to furnish the N-acylated products in good yields under solvent-free conditions. The reactions of various sulfonamides were studied with different carboxylic acid anhydrides including the less reactive benzoic and pivalic anhydrides, in the presence of 3 mol % ZnCl₂ as the catalyst. Carboxylic acids were also successfully used as acylating agents via the mixed anhydride method.     

三卤化硼Lewis酸性的密度泛函理论研究

用密度泛函理论的DFT-LDA/NL方法研究BX₃(X=F,Cl,Br)分子的Lewis酸性.计算BX₃分子的硬度时,采用一个可供选择的方法.该法是密度泛函理论的Janak定理的推广.结果表明,分子硬度是BX₃Lewis酸性的最好表征.应用Pearson的软硬酸碱(HSAB)原理可以合理地解释BX₃酸性的变化规律     

丙酮酸分子结构与振动光谱的密度泛函理论研究

用密度泛函方法BLYP、B3LYP和从头算Hartree-Fock(HF)方法在6-31G*基组水平上对丙酮酸分子的几何结构（甲基的重叠式和交错式两种构象）和振动光谱分别进行了优化和计算,并给出了各种频率所对应的红外强度及拉曼活性,对光谱进行了指认。结果表明：在丙酮酸分子的两种构象中,重叠式比较稳定*B3LYP计算得到的构型参数与实验结果比较一致;在振动频率的计算中,BLYP未标度力场所计算的非CH3伸缩振动基频预测值和实验值的平均绝对偏差为10.4cm-1;而HF标度力场的平均绝对偏差为17.9cm-1。说明两者的结果与实验观测频率比较吻合,但B3LYP的频率计算值偏差（38.3cm-1）较大。根据振动频率的势能分布和红外光谱强度对此分子的振动基频进行了理论归属。     

Temperature-programmed desorption of water and ammonia on sulphated zirconia catalysts for measuring their strong acidity and acidity distribution

Temperature-programmed desorption (TPD) of water and ammonia over ZrO₂ and sulphated ZrO₂ prepared by different methods has been investigated for measuring strong acidity and acidity distribution on sulphated zirconia-type solid super-acid catalysts. The TPD of water provides a simple reliable method for this purpose because of the high stability of water molecules under redox conditions     

Structure,epr parameters,and reactivity of organic free radicals from a density functional approach

Summary A recently introduced density functional incorporating gradient corrections and some Hartree-Fock exchange has been used to study the structures, properties, and reactivity of representative organic free radicals. A general theoretical model has been introduced, in which standardized grid, functional, and orbital basis set are used to compute geometrical parameters, vibrational frequencies, and one-electron properties. The results are compared with available experimental data from diatomic to polyatomic radicals. All the geometric and electronic parameters compare favourably with available experimental data and with the results of refined post Hartree-Fock computations. Also the thermodynamics and kinetics of a representative unimolecular reaction (isomerization of formaldehyde radical cation) are well reproduced. These findings together with the very favourable scaling of the computations with the number of electrons suggest that the density functional approach is a promising theoretical tool for the study of relationships between structure and properties of large free radicals.     

Lithium 2,3-dihydro-1-benzothiophene-1,1-dioxide: synthesis, characterization, DFT calculations, and reactivity toward aldehydes and azomethines

The sulfonyl carbanion derived from 2,3-dihydro-1-benzothiophene-1,1-dioxide and its lithium salt has been investigated by DFT calculations. NMR and IR spectroscopic analyses showed that the lithium sulfonyl carbanion exists in solution as a monomer in equilibrium with a dimer. The lithium carbanion was treated with aldehydes and azomethynes to give chiral hydroxy and amino derivatives. The stereochemistry of the products and the diastereoselectivity of the reaction were investigated.     

Gas-phase acidity, bond dissociation energy and enthalpy of formation of fluorine-substituted benzenes: A theoretical study

A variety of theoretical methods have been used to study the gas-phase acidity of benzene and its eleven fluorine-substituted derivatives: fluorobenzene, three isomers of difluorobenezene, three isomers of trifluorobenzene, three isomers of tetrafluorobenzene and 1,2,3,4,5-pentafluorobenzene. The high-level ab initio methods, G3//B3-LYP and CBS-QB3, are shown to reproduce experimental data to within an average of 1.9 and 1.4 kcal mol⁻¹, respectively. Of the lower-cost methods studied, M05-2X and MP2 showed the best overall performance with mean absolute deviations of just 1.2 and 1.1 kcal mol⁻¹, respectively. The effect of substitution and position on the acidity of the protons in the various compounds are studied and the structure-reactivity trends in these heterolytic C-H bond dissociation energies (BDEs) are compared with the corresponding homolytic C-H BDEs for the same species.     

阳离子寡肽序列的合成及生物学研究——推荐一个针对化学生物学专业学生的研究型实验

采用多肽固相合成技术制备了寡肽序列RRRRRRRR(R8)。通过电喷雾电离质谱仪对序列的相对分子质量进行了表征。进一步通过琼脂糖凝胶电泳和细胞内吞实验考察寡肽序列在生物学研究方面的应用。本实验可以加深学生对有机化学、高分子化学及生物化学的理解与运用,培养学生分析问题和解决问题的综合能力。