等电子-等自旋与非等旋反应的G2(MP2)和G2研究

我们在前文［1－2］中分别用MP2－4／6－31G**／／MP2／6－31G**及MP4／6－311G（2df，Zpd）／／MP2／6－31G**研究了一些双原子氢化物、卤化物、硫化物和氧化物的化学反应的烂变·这些化学反应按如下类型分为四组，即（1）反应物与生成物之间为等电子一等自旋关系，（2）价层等电一等旅，（3）等施和（4）非等旅·结果表明，MP4／6－3fiG（2才，ZPd）对于（1），（2）和（3）类反应，基本上与实验误差小于士15kJ·mo－‘而对非等旋反应仍有较大误差；MPZ－4／6－31G””只对（1）类反应较好．由于PoPle等人近几年来创立的Gaussi…     

有机复习中的专题讲座

有机复习的基本任务是架设以CH4、CH3COOC2H5为代表物的“分条分块”体系和以“CH3CH3←CH2＝CH2←CH＝CH络”关系。同时,还必须针对高考热点,开辟若干专题进行深入的复习。一、燃烧问题专题印发下列问题师生共同讨论：1．两个通式烃类燃烧通式：CxHy＋（X＋y／4）O2→XCO2＋y／2H2O烃的衍生物燃烧通式：Cx＋HyOz＋（x＋y／4－Z／2）O2→XCO2＋y／2H2O2．四种量（1）体积变化量气态烃（或气态烃的混合物）CxHy与足量氧气混合点燃,然后恢复到原状况（水为蒸气）,则总体积变化量是烃体积的（y／4－1）倍。显然,当y＝4时…     

四唑及其衍生物的理论研究（6）

对7个肼基四唑衍生物进行了HF／6－31G水平的几何构型全优化及MP2／6－31G／／HF／6－31G水平的总能量计算．结果表明，四唑环基本上取平面构型，肼基不与环共面．键长与重叠布居之间不存在平行关系．环上N1和N4原子荷负电多、利于质子化．1H．肼基四唑的HOMO－LUMO能级差（△E）较2H式的大，中性分子的△E教相应的负离子的大．还计算研究了7个标题物的红外光谱并由此求得了它们的热力学性质．     

CH3S自由基H迁移异构化及脱H2反应的直接动力学研究

采用密度泛函方法（MPW1PW91）在6．311G（d,p）基组水平上研究了CH3S自由基H迁移反应CH3S→CH2SH（R1）,脱H2反应CH3S→HCS＋H2（R2）以及脱H2产物HCS异构化反应HCS→CSH（R3）的微观动力学机理．在QCISD（t）／6．311＋＋G（d,p）／／MPW1PW91／6．311G（d,p）＋ZPE水平上进行了单点能校正．利用经典过渡态理论（TST）与变分过渡态理论（CVT）分别计算了各反应在200-2000K温度区间内的速率常数K^TST和k^CVT,同时获得了经小曲率隧道效应模型（SCT）校正后的速率常数萨k^CVT/SCT．结果表明,反应R1,R2和R3的势垒△E^≠分别为160．69,266．61和241．63kJ／mol。R1为反应的主通道．低温下CH3S比CH2SH稳定,高温时CH2SH比CH3S更稳定．另外,速率常数计算结果显示,量子力学隧道效应在低温段对速率常数的计算有显著影响,而变分效应在计算温度段内对速率常数的影响可以忽略．     

CH自由基与O2反应的从头算研究

采用量子化学从头算法（UMP2／6－31G**水平），从理论上研究了CH＋O2反应的两个主要通道.根据计算所得的反应诸途径（连接反应物Cn＋）及两个通道的最终产物）讨论了复杂的反应机理．发现反应过程涉及O2的第一激发态1△g，且沿反应途径有势能面相交，反应途径中包括多个中间体及过渡态．     

甲基重氮烷阳离子（CH3N2^＋）与DNA碱基的甲基化反应

在B3LYP／6．31G^＊＊和MP2／6．311G^＊＊水平上,计算了终致癌物甲基重氮烷阳离子（CH3N2^＋）在气相和水溶剂中与四种DNA碱基上10个亲核位发生甲基化过程的反应机理．结果表明：在气相和溶剂中,终致癌物CH3N2^＋对碱基上相应亲核位的甲基化反应过程,活化能都比较小（〈33．5kJ／mol）,是容易进行的放热反应．所以,二甲基亚硝胺一旦形成终致癌物,则很容易与碱基形成癌变物．     

1,2-二硒-3，4-二硫方酸的从头计算

在RHF／STO－3G、STO－3G和3－21G（仅对ZE型）水平上，用abinitioSCF方法优化得到1，2－二硒－3，4－二硫方酸（3，4－二巯基－3－环丁烯－1，2－二硒酮）三种平面异构体的平衡构型，进一步用3－21G／／STO－3G（对ZZ和EE型）方法计算总能量，发现三种平面导构体中ZZ型是最稳定构象，ZE型次之，并与1，2－二硒方酸和3，4－二硫方酸从头算结果作了比较，用abinitio数值方法在STO－3G水平上计算了三种异构体的谐振动频率．     

H＋CH3NO2→H2＋CH2NO2反应途径和变分速率常数计算研究

采用MP2（FULL）／6－311G**从头算方法，优化了H＋CH3NO2——H2＋CH2NO2反应的过渡态结构，得出该反应的正逆反应的活化位垒分别是82．73和57．14 kJ·mol－1 ．沿IRC分析指出该反应是一个H—H键生成和C—H键断裂的协同反应，而且在反应途径上存在一个引导反应进行的振动模式，这一反应模式引导反应进行的区间在- 0．7～0．2（amu）1/2·a0之间；在 1000～1400 K温度范围内，运用变分过渡态理论（CVT），计算了该反应的速率常数，计算结果与实验相一致．     

Fe－Mn催化剂对F－T合成反应的催化性能Ⅱ．中后期反应性能

 采用固定床积分反应器，详细考察了F－T合成反应用Fe－Mn催化剂运行900和1800h后的中后期反应性能．结果表明，该催化剂仍维持着较高的催化活性及稳定性；与初期反应性能相比，运行900h后CH4选择性有明显升高的趋势，运行1800h后CH4选择性进一步升高．运行2200h后，通过降低原料气的H2／CO比和提高反应压力，可明显改善烃产物的选择性．在n（H2）／n（CO）＝0．62，GHSV＝2300h－1，p＝3．02MPa和θ＝283℃的条件下，CO转化率可达75．6％，总有效烃（C＝2～4＋C＋5）的选择性可达89．0％，CH4选择性为5．7％．这表明该催化剂具有良好的可操作性，且特别适合于由煤制合成气制液体燃料和C2～4低碳烯烃，在浆态床反应器中有潜在的应用前景．     

(CH2)2N和(CH3)2NH+的密度泛函理论计算

用密度泛函理论UB3LYP／6-31G（d,p）方法研究了二甲胺自由基（CH3）2N及其质子化离子（CH3）2NH 的构象和超精细结构．在由构象研究得到的两种自由基的最稳定结构上,用密度泛函的UB3LYP和UB3PW91方法及从头计算的UHF、UMP2（FULL）方法计算了α-质子、β-质子和N核上的超精细偶合常数A（Hα）、A（Hβ）和A（N）结果表明：两种自由基中甲基内旋转的位垒均很低,分别为0．46kJ·mol-1（（CH3）2NH ）和2．6kJ·mol-1（（CH3）2N）．UB3LYP／6-31G（d,p）和UB3PW91／6-31G（d,p）计算的A（Hα）、A（Hβ）和A（N）与ESR实验结果符合得很好,UMP2／6-31G（d,p）方法的计算值与实验值符合得也较好．     

Ab Initio Study of Endo/Exo and Diastereofacial Selectivities in Diels-Alder Reactions between Chiral Butenolides and Cyclopentadiene

Diels-Alder reactions of cyclopentadiene with crotonolactone and beta-angelica lactone have been studied using ab initio methods at the MP3/6-31G//RHF/3-21G and MP2/6-31G//RHF/6-31G levels. The transition states corresponding to the formation of different stereoisomers and diastereoisomers have been located. The results obtained show that the correct endo/exo selectivity is only obtained when polarization functions are included in the basis set. However, syn/antiselectivity is correctly described at all levels of calculation.     

3-羟基-2-吡啶亚胺异构反应的机理

在RHF-6-31G,MP2/6-31G和MP2/6-31G水平上,对3-羟基-2-吡啶亚胺的气相、水分子作为催化剂的异构化反应进行了研究,结果表明,气象异构难于进行,水分子作为催化剂参与反应过程是目标反应所循的反应路径。     

乙烯醇锂的从头算研究

用限制的HF/3-21G和HF/6-31G^*优化乙烯醇锂的几种可能构型,比较了它们的稳定性.用限制的HF/3-1G,从乙醛开始,探讨了气相反应生成乙烯醇锂的机理,并在MP2水平上用6-31G^*基组计算了反应热.     

乙烯醇钠的从头算研究(英文)

在ＲＨＦ／３－２１Ｇ和ＲＨＦ／６－３１＋Ｇ水平上优化了乙烯醇钠的的平衡构型及过渡态，比较了不同构型的稳定性。在ＲＨＦ／６－３１＋Ｇ水平上探讨了气相中由乙醛和氢氧化钠生成乙烯醇钠的机理。并在ＭＰ２（ｆｕｌ）／６－３１＋Ｇ／／ＭＰ２（ｆｕｌ）／６－３１＋Ｇ水平下计算了反应热     

AB initio study of thermodynamic stability and structure of cage molecules B4N4H8 and Be4O4H8

Stable molecular structures of heterocubane systems B₄N₄H₈ 2 and Be₄O₄H₈, isoelectronic to the cubane molecule, are investigated by ab initio (RHF/6-31G**, MP2(full)/6-31C**, and MP2(full)/6-311+ + G**) methods and are shown to be highly thetmodynamically stable. Decomposition of structure 2 into two 1,3,2,4-diazadiboroethidine molecules 6 or four iminobomne NBNH molecules 11 is an endothermal process taking 10.1 (RHF/6-31G**), 39.6 (MP2(full)/6-31G**) kcaUmole and 140.6 (RHF/6-31G**), 161.4 (MP2(full)/6-31G**) kcal/mole, respectively. Decomposition of structure 3 into two 1,3,2,4-dioxydi-beryllothidine molecules 12 or four molecules 13 is also an endothermal reaction taking 22.1 (RHF/6-31G**), 39.8 (MP2(full)/6-31G**) kcal/mole and 127.1 (RHF/6-31G**), 155.2 (MP2(full)/631G**) kcal/mole, respectively. The geometrical characteristics of simple molecules BeH₂ 15, Be₂ 16 and 17, Be₂H₂ 18, Be₂H₄ 19, BeO 20, and Be₂O₂ 21 are calculated. Translated from Zhumal Struktumoi Khim ii, Vol. 41, No. 1, pp. 3-13, January–February, 2000     

Ab initio method study on the isomerization of 3-amino-2-pyridone

Ab initio caculations with RHF/6-31G and MP2/6-31G have been used to study the isomerization of 3-amino-2-pyridone in gas-phase and in water. The results obtained show that 3-amino-2-pyridone is isomerized into 3-amino-2-hydroxy pyridine via a four-center cyclic transition state in the gas-phase, and via a six-center cyclic transition state in water. The activation energies of this reaction are 226.3336(RHF/6-31G) and 171.2269(MP2/6-31G) in gas-phase, and 81.6398(RHF/6-31G) and 59.8668(MP2/6-31G) kJ mol⁻¹ under the condition of a single water molecule as the catalyst, respectively.     

Hartree-Fock, Møller-Plesset calculations and dynamic NMR study of 3,3-dimethoxy-1-(imidazolidin-2-ylidene)propan-2-one

The experimental (1)H, (13)C NMR spectra of 3,3-dimethoxy-1-(imidazolidin-2-ylidene)propan-2-one were recorded in CDCl(3) at temperature range 213-323 K. The variable temperature spectra revealed a dynamic NMR effect which is attributed to restricted rotation around the C=C double bond. Fast exchange processes of deuterium atoms between CDCl(3) and 3,3-dimethoxy-1-(imidazolidin-2-ylidene)propan-2-one or fast exchange of proton between nitrogen and oxygen atoms of carbonyl group is also revealed by broadening of N-H (singlet) proton NMR signals. Proton and carbon theoretical chemical shifts of the title molecule were calculated by using RHF and MP2-GIAO levels and different basis sets in gas phase at 298 K. The calculated proton chemical shifts show that the experimental values have no agreement with theoretical values, but for carbon chemical shifts a good agreement achieved by using RHF with 6-31G basis set and MP2/3-21G, 6-31G basis sets. Discrepancies are attributed to either the limitations of calculating program, because the change of the structure while rotation are not considered. The results showed that to select of basis set has more important rule, because RHF-GIAO level calculation with 6-31G basis set in gas phase can excellently reproduce the (13)C NMR spectrum. Moreover, MP2/3-21G, 6-31G calculation has not significant influence on (13)C NMR chemical shifts with respect to RHF-6-31G.     

Ab initio molecular orbital calculations for 3,6-dihydro-1,2-dithiin and 3,6-dihydro-1,2-dioxin

Optimized geometries and total energies for the conformers of 3,6-dihydro-1,2-dithiin ( 2 ) and 3,6-dihydro-1,2-dioxin ( 3 ) were calculated at several ab initio MO levels: RHF/3-21G(*), RHF/6-31G*, MP2/6-31G*, and MP2/6-31G*/ /RHF/3-21G(*). For the dioxin, in addition to the above levels the corresponding nonextended basis sets ab initio methods were also carried out. The dithiin results are compared with those of simple disulfanes, HSSH and (CH₃)₂S₂, whose optimized geometries agree closely with the observed structures, which is the gauche (C₂ symmetry). For the disulfanes, the gauche geometries from RHF/3-21G(*) are in good agreement with the observed structure while the RHF/3-21G results best fit the dioxin. Pertinent structural data at the RHF/3-21G(*) for the half-chair (C₂) dithiin are: bond lengths, ? SS? , ? CS? , ? CC?, and ? C?C? , 2.050, 1.817, 1.515, and 1.317 Å, respectively; bond angles, CSS, ?CCS, and C?CS, 98.0, 114.2, and 127.8°, respectively; CSSC dihedral angle of 63.2°; and twist angle of 36.5°. The total energy for half-chair dithiin at MP2/6-31G*//RHF/3-21G(*) is less than the planar (C_2v) and the half-boat (C_s) structures by 69.67 and 29.05 kJ/mol, respectively. The calculated structural data (vs. observed) at RHF/3-21G for the half-chair dioxin are: bond lengths, ? OO? , ? CO? , ? CC?, and C?C, 1.464 (1.463), 1.454, 1.509, and 1.313 Å (1.338 Å), respectively; bond angles, COO, ?CCO, and C?CO, 105.0, 109.8 (110.3), and 120.7° (119.9°), respectively; COOC dihedral angle of 79.7° (80 ± 2°); and twist angle of 39.0 (38.3°). The total energy for half-chair dioxin at MP2/6-31G//RHF/3-21G is less than the planar and the half-boat structures by 70.35 and 42.85 kJ/mol, respectively. The total energies calculated at the extended basis sets (*) ab initio levels for the C₂ symmetry dioxin are much lower than those of the nonextended basis sets. © John Wiley & Sons, Inc.     

Electronic effects of conjugated enones on their reactivity in transformations of ADDN type

Using RHF/3-21G, RHF/6-31G(d, p), MP2/6-31G(d, p), B3LYP/6-31G(fd, p) approximations the structure and ¹³C NMR spectra of 2-alkylsubstituted cyclohexene-2-ones and 2-alkylacroleins are studied and calculated. In the series of 2-alkylcyclohexene-2-ones the effect of the substituent on a deviation from coplanarity of the C=C-C=O fragment is more expressed in comparison with 2-alkylacroleins. This deviation (5°) is not enough to explain the observed properties of 2-alkylcyclohexene-2-ones due to disturbed conjugation. The particular behavior of (R)-4-mentenone in reactions of 1,4-addition and ozonolysis is explained by a more expressed +I-effect of the alkyl substituent in α-position.     

二氟硅杂环丙烯异构化反应的理论研究

近十几年来，硅烯（：SN小'一到作为活性中间体的研究引起化学界的广泛兴趣，形成了内容丰富的硅烯化学．1975年Ilass＊等研究了硅烯和乙炔的加成反应，指出该反应的中间体为硅杂环丙烯，硅杂环丙烯异构化为硅甲基乙炔．Boatz问等利用：j－ZIG（d）基组对金属杂环丙烯小［＊xZC