分子二阶超极化率γ的Hartree-Fock极限值

用共轭微扰Hartree-Fock (CPHF)方法,在RHF/x-aug-cc-pVXZ (x=0～8, X=T, Q)水平上计算了He, Ne, H₂, FH, CO和OH^-等原子和分子的二阶超极化率γ.发现当基组增大时,超极化率γ起初趋向于收敛,但当基组继续增大时,γ值又趋于发散,即γ随基组的增大出现一个拐点.拐点对应的γ值与数字轨道计算的γ值符合得较好.初步讨论认为γ值的发散是由于基组在近核区域的不完全性造成的.建议用拐点处的γ值作为Hartree-Fock极限值.     

二阶超极化率γ的Hartree-Fock极限值的再研究

用有限场(FF)方法,在ROHF/x-aug-cc-pVXZ(x=1～5或7,X=T,Q)水平上计算了C,N,O,F,OH和OH⁺等开壳层原子和分子、离子的二阶超极化率γ.与闭壳层原子和分子的计算结果相类似,γ随基组的增大出现一个拐点.拐点对应的γ值与数字轨道计算的γ值符合得较好,其平均相对误差分别为1.79%(x-aug-cc-pVTZ)和1.91%(x-aug-cc-pVQZ),故计算二阶超极化率γ不需使用g函数.进一步研究表明,用x-aug-cc-pVTZ系列基组不仅可以得到γ的Hartree-Fock极限值,而且可以用来作较准确的二阶超极化率相关效应的计算.     

端基取代的长链硅烷二阶超极化率的量子化学研究

对端基取代的一维无限长反位硅烷H₂N-(SiH₂-SiH₂)_n-NO₂的二阶超极化率进行了系统的量子化学研究. 通过仔细检验和选择外场强度, 采用9个外场强度(0.0000, ±0.0008, ±0.0012, ±0.0016, ±0.0020 a.u.)计算的体系能量来确定4阶场强展开式中的5个系数, 从而得到可靠的二阶超极化率. 建议数据拟合时用二阶超极化率单元值的平均值形式γ(n)/n作为拟合对象, 同时用1/n的2阶多项式作为拟合函数, 以得到无限长链的二阶超极化率极限值. 拟合数据范围的选择应该使该数据范围得到的极限值与其临近数据范围得到的极限值的均方偏差最小. 分子构型的优化使计算的二阶超极化率增加大约20%, 在基组中增加极化函数使二阶超极化率在无限长链时的极限值减少大约15%. 相关效应的影响最大, MP2的结果比RHF的结果增加近一倍. 根据本文最高水平MP2/6-31G(d)//RHF/6-31G的计算, 端基取代的一维无限长反位硅烷H₂N-(SiH₂-SiH₂)_n-NO₂的二阶超极化率的每单元极限值为0.8364×10⁶ a.u.     

高级量子化学从头计算法研究N2和H2O分子间相互作用

在MP2/6-311++G(3d,3p)电子相关校正水平上,对N₂和H₂O分子间可能存在的氢键复合物进行全自由度能量梯度优化,发现了一个接近于直线的弱氢键总能量极小结构(1),进一步在高级电子相关校正的MP4SDTQ和CCSD(T)水平,用6-311++G(3d,3p)基组加上(3s3p2d1f)键函数,用MP4和CCSD(T)计算的结构1的结合能分别为-5.061kJ/mol和-4.715kJ/mol.     

量子化学研究水对Adenine-Thymine碱基对构型的影响

利用Hartree-Fock方法, 选取6-31G*基组对Adenine-Thymine-Water氢键复合物可能存在的构型进行了优化, 然后用DFT PBE方法, 选取6-311＋＋G(3d, 3p)基组对复合物的结合能进行计算, 结果表明水与DNA中配对碱基的相互作用, 不会显著影响碱基对的稳定性, 水的存在使得碱基对的扭转构型更接近真实DNA中碱基对的螺旋状结构.     

CH3NO2+X(X=H,OH, CH3, CH2[^3B1], O[^3P])→CH2NO2+XH吸氢反应过渡态 结 构和反应位垒的DFT计算研究

采用DFT(B3LYP)方法,分别在6-311g(d,p),6-311++g(d,p)和自洽相关基组cc-pVIZ水平上优化了基态硝基甲烷和自由基H,OH,CH3,CH2[^3B1]以及O[^3P]等发生吸氢反应时的过渡态结构,并计算了反应的位垒。研究表明,对同一反应,不同基组下优化得到的过渡态几何结构基本一致;反应位垒数值的大小也基本接近,经校正,硝基甲烷同自由基反应位垒的理论计算值同实验结果基本吻合。     

π和σ体系彻底分离的高度定域的键轨道基组的建立

高度定域的、对称的、键轨道基组的建立是一个多步的计算程序：(1)以定域片断轨道[φk,φi,φj]为基,对分子作有条件的RHF运算,算得FUL和DSI°态的片断分子轨道[Φ°l',Φ°n,Φ°m]和[Φl,Φn,Φm]。在基组[φk,φi,φj]中,φi∈双占据和空σ片断分子轨道(FMOs)组,φj∈πFMO组,φk∈单占据σFMO组,它们都精确地定域在各自的片断内;(2)利用Φ°l'与Φ°l间的重叠积分值(Sl'l>0.5),可以从DSI°态中,自动地选出Ns个对称的、由单占据轨道线性组合而成的分子轨道Φ°l'=Σakl'φk(k=1,2,…,Ns),接着,用Φ°l'取代FUL态中同类的、非对称轨道组Φl=Σaklφk(k=1,2,…,Ns);(3)以上述新的轨道组[Φ°l',Φn,Φm]为基(其中,Φ°l'∈DSI°态,它们离域于整个分子;双占据及空σFMO组Φm和πFMO组Φm属于FUL态),按FUL态的条件,再次对分子作有条件的RHF运算,从中得到一组对称的、闭壳层正则FMOs,而且每一个FMO均有正确的电子占据数;(4)利用Perkin原理,将第3步所得的正则FMO组定域成一个对称的键轨道基组[Φl',Φn',Φm']。在这个基组中,π体系Φm'与σ构架Φn'是彻底分离的,而且这两个轨道组始终精确地定域在各自的片断内。     

孪函数多电子基组在LiH分子方面的应用

选择从头算STO-6G基组,以孪函数Ⅳ电子基组计算LiH分子的基态(s=0)和激发态(s=1).结果表明,无需全部孪函数N电子基组,只要适当选择少数基组即可达到所需精度.     

从头计算法分子轨道绘图程序

在前文中,我们报道了以Slater函数(STO)和类氢函数为原子轨道基组的分子轨道绘图程序,文介绍以Gauss函数(GTO)为基组的从头计算分子轨道绘图程序,该程序可绘制各类型(s,p,d等)GTO表示的原子轨道和以STO-GTO系基组构成的各种分子轨道ψ或|ψ|²的截面立体图及等值图,利用从头计算的结果,所绘制的图形能很好的反映从头计算法本身的特点。     

π和σ体系彻底分离的高度定域的键轨道基组的建立

高度定域的、对称的、键轨道基组的建立是一个多步的计算程序：(1)以定域片断轨道[φk,φi,φj]为基,对分子作有条件的RHF运算,算得FUL和DSI°态的片断分子轨道[Φ°l',Φ°n,Φ°m]和[Φl,Φn,Φm]。在基组[φk,φi,φj]中,φi∈双占据和空σ片断分子轨道(FMOs)组,φj∈πFMO组,φk∈单占据σFMO组,它们都精确地定域在各自的片断内;(2)利用Φ°l'与Φ°l间的重叠积分值(Sl'l>0.5),可以从DSI°态中,自动地选出Ns个对称的、由单占据轨道线性组合而成的分子轨道Φ°l'=Σakl'φk(k=1,2,…,Ns),接着,用Φ°l'取代FUL态中同类的、非对称轨道组Φl=Σaklφk(k=1,2,…,Ns);(3)以上述新的轨道组[Φ°l',Φn,Φm]为基(其中,Φ°l'∈DSI°态,它们离域于整个分子;双占据及空σFMO组Φm和πFMO组Φm属于FUL态),按FUL态的条件,再次对分子作有条件的RHF运算,从中得到一组对称的、闭壳层正则FMOs,而且每一个FMO均有正确的电子占据数;(4)利用Perkin原理,将第3步所得的正则FMO组定域成一个对称的键轨道基组[Φl',Φn',Φm']。在这个基组中,π体系Φm'与σ构架Φn'是彻底分离的,而且这两个轨道组始终精确地定域在各自的片断内。     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.     

Sulfur-directed metal-free and regiospecific methyl C(sp3)–H imidation of thioanisoles

Regiospecific and direct imidation of the methyl C(sp³)–H bond of thioanisoles is realized under mild and metal-free conditions with N-fluorobis(benzenesulfonyl)imide as an oxidant and nitrogen source. Proposed mechanism suggests that thionium ion intermediates and a Pummerer-type reaction are involved. The imidation has advantages such as high step-economy, excellent functionality tolerance, and regiospecificity, giving structurally diverse imidation products.     

Selective syntheses of 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones via temperature-dependent Rh(II)-carbenoid-mediated 2H-azirine-ring expansion

The Rh(II)-catalyzed reaction of 2-carbonyl-substituted 2H-azirines with ethyl 2-cyano-2-diazoacetate or 2-diazo-3,3,3-trifluoropropionate provides an easy access to 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones. These compounds can be selectively prepared from the same starting material using temperature as the only varied parameter. The 2-azabuta-1,3-diene intermediate, a common precursor for both heterocyclic products, isomerizes into 2H-1,3-oxazine under kinetic control, while 1H-pyrrol-3(2H)-one is the sole product of the reaction at elevated temperatures. According to DFT-calculations a one-atom oxazine ring contraction involving ring-opening to a 2-azabuta-1,3-diene intermediate, followed by a 1,5- and 1,2-prototropic shift leads to the consecutive formation of imidoylketene and azomethine ylide, which then further undergo cyclization to the pyrrole derivative.     

Copper catalyzed/mediated synthetic methodology for ebselen and related isoselenazolones

Scope of the copper catalyzed/mediated selenium-nitrogen coupling reaction has been studied for the synthesis of isoselenazolones. It is noticed that the 2-chloro, 2-bromo-, and 2-iodo-aryl amides substrates can be exploited in the selenium-nitrogen coupling reaction by employing 25-100 mol % of CuI/1,10-phenanthroline (L) and potassium carbonate as a base in DMF. Furthermore, electron rich 2-chloro-arylamides also underwent selenium-nitrogen coupling reaction to give biologically important selenium-nitrogen heterocycles. Also, copper-catalyzed selenium-nitrogen coupling reaction has been meticulously applied for the synthesis of diaryl diselenides having methoxy, amine, and amide functionality from respective aryl iodides in the presence of stoichiometric amount of succinimide as an external Se-N coupling partner.     

Knoevenagel condensation catalyzed by novel Nmm-based ionic liquids in water

A series of novel N-methyl morpholine (Nmm) based ionic liquids with 1,2-propanediol group were synthesized and used as catalysts for Knoevenagel condensation at room temperature in water. Under the effect of the catalyst, various aldehydes or aliphatic ketones could react with a wide range of activated methylene compounds well, including malononitrile, alkyl cyanoacetate, cyanoacetamide, β-diketone, barbituric acid, 2-arylacetonitrile and thiazolidinedione. Furthermore, most of the products could be separated just by filtrating and washing with water. Additionally, the catalyst is recyclable and applicable for the large-scale synthesis.     

Construction of polyheterocyclic spirotetrahydrothiophene derivatives via sulfa-Michael/aldol cascade reaction

A series of polyheterocyclic spirotetrahydrothiophene derivatives were obtained in moderate to excellent yields via a catalyst-free sulfa-Michael/aldol cascade reaction of chalcones 1 and commercially available 1,4-dithiane-2,5-diol 2 under mild conditions. We also present the first asymmetric sulfa-Michael/aldol cascade reaction of chalcones 1 and commercially available 1,4-dithiane-2,5-diol 2 with moderate to good enantioselectivities catalyzed by readily available chiral phase-transfer catalysts (PTCs).     

Suzuki-Miyaura reactions of the soluble guanylate cyclase inhibitor NS2028: a non-product specific route to C-8 substituted analogues

Both soluble guanylate cyclase (sGC) inhibitors ODQ 1 and NS2028 2 are synthesized via improved protocols. In the former case treating 3,4-dihydroquinoxalin-2(1H)-one oxime 8, which can be prepared in two steps from 1,2-benzenediamine, with 1,1′-carbonyldiimidazole (CDI) gives the dihydro-ODQ 10 that in the presence of KMnO₄ oxidises to give ODQ 1 in an overall yield of 46% starting from 1,2-benzenediamine. In the latter case, the synthesis affords NS2028 2 from 2-amino-4-bromophenol 3 in three steps with an overall yield of 85% and avoids the need for chromatography. Furthermore, Suzuki-Miyaura reaction conditions are described that enable the preparation of 8-aryl and 8-heteroaryl derivatives of NS2028 directly from NS2028 2. Finally, demethylation of the 8-(methoxyphenyl) substituted analogues afforded the 8-(hydroxyphenyl) derivatives 40-42. All new products are fully characterised.