CO在Ni表面甲烷化反应的CNDO/2研究

本文用CNDO/2方法,选择Ni_5、Ni_6原子簇模拟Ni(100)的三个典型位置,对CO的吸附情况和CO在Ni表面解离为活性碳原子的方式进行了研究,进而探讨了甲烷化反应的机理。     

Diels-Aider反应区域选择性的CNDO/2研究

用6-甲基-2,4-庚二烯与乙酸乙烯酯环加成然后氢化水解而合成薄荷醇的方案中存在一个区域选择性的问题.采用 CNDO/2法计算轨道能量和系数而用前线分子轨道法预言薄荷醇不是主要产物,而6-甲基-2,4-庚二烯二聚的主要产物应具有文中Ⅷ的结构.另用16个反应的区域选择性实验结果来检查方法的可靠性.结果14个预言符合实验;另两例的失败可归因于前线轨道法的粗糙性.     

CNDO/2及其一级近似——CNDO/2-FA

CNDO/2一级近似法CNDO/2-FA)是一种值得推荐的方法.此法从Hückel理论所得的密度矩阵出发,构成第一个Fock矩阵,对角化并得到新的密度矩阵后,即转向最后结果的计算.由于略去了自洽迭代,可节省数倍的计算量.已从几何构型、力常数、解离能、电离势、质子亲合势、转动位垒、前线轨道能量等多方面进行考察,一级近似结果皆与自洽结果很相近,仅电荷分布稍不满意.MNDO的一级近似则不可用。     

丙烯分子几何形态稳定性的CNDO/2计算

利用CNDO/2量子化学近似计算方法,对几种不同几何形态的丙烯分子稳定性进行了计算,结果表明,处于C(2)—C(3)单键反式及对称性较好的几何形态,α—端碳C_((1))~(δ-)负净电荷和间碳C_((2))~(δ+)正净电荷均较多,最稳定。得到的丙烯分子为中性分子,正负电荷分别为+0.591193e~-和-0.591194e~-,轨道集居数为C_3~(12.37768e-)H_6~(5.61233e-),C_3~(0.37768e-)为电子授体,H_6~(-0.3368e-)为受体。该形态使其HCO化有利。消除了SCCC-LCAO-MO法对于丙烯几何构型计算出现的一些矛盾,本计算更符合实验事实,更合理一些。     

2-取代吡啶衍生物的CNDO/2计算和分子光谱研究

本文用CNDO/2方法计算了吡啶及其2-取代衍生物,测了其紫外光谱.通过红外,紫外光谱和量子化学计算的综合分析,确定2-吡啶酮与2-羟基吡啶是互变异构体,并推断2-氨基吡啶的互变异构体存在,从而很好地得到了此系列紫外光谱的线性规律.     

辛烯与苯酚烷基化反应的CNDO/2-PMO的研究

本文用CNDO/2-PMO方法研究了在酸催化下辛烯与苯酚的烷基化反应。计算结果和实验结果表明,反应速度主要由烯酸络合物的活性所决定。由于酸使烯烃最低空轨道的能量降低,从而引起催化作用。能量降低愈多,烯酸络合物的催化活性愈大。反应的邻、对位的选择性主要由烯酸络合物和苯酚的前沿轨道的相互作用微扰能所决定。烯酸络合物碳阳离子的前沿轨道系数愈大,反应选择性愈高。本文还初步讨论了环取代反应和醚生成反应之间的相互关系。     

α-取代环戊酮类抗癌药物的CNDO/2计算

许多天然倍半萜类化合物具有明显的抑癌作用,Lee等认为其活性基团是O=C—C=CH_2。曾昭钧等认为羰基和环戊基可能是这类化合物的有效结构。他们合成了一系列α-取代环戊酮类化合物。体外试验表明,这些化合物对小鼠艾氏腹水癌有不同的抑制作用,其有效程度随取代基的不同而异(见表1)。本文用CNDO/2方法对6种α-取代环戊酮类化合物作了计算,试图阐明取代基、量子化学指数、抑癌活性的关系,以期对有目的地合成这类药物有所帮助。     

丁烯在Fe-O晶格上吸附络合物的CNDO/2计算

在很多种丁烯氧化脱氢制丁二烯的催化剂中,铁系尖晶石具有反应选择性高的独特优点. 三种正丁烯异构体在Bi_2O_3-MoO_3及Sn-P-Li等氧化物催化剂上的反应机理和三者转化为丁二烯的速度常数已有较多的研究论述.但它们在铁系尖晶石型催化剂上     

CNDO/2法计算二茂锆卤化物的电子结构

本文将Pople的闭壳层CNDO/2程序改编成将原子中s,p,d亚层分开处理,并扩展到可计算锆化合物的CNDO/2-TM程序;选取了锆的有关参数;计算了Cp_2ZrX_2(X=F,Cl)分子的电子结构.得到的氯化物分子轨道的能级次序和间隔与光电子能谱相符.计算的偶极矩为5.88D,与实验值相近.计算结果还说明Cp_2ZrX_2是有一定离子性的共价化合物.中心锆原子约呈 1价.金属锆的5s轨道参与茂环的σ键,5p轨道通过移入电子参与茂环σ键,而4d轨道则参与茂环的π键,但成键所占成分不大.Zr-F键的离子性占51％,Zr-Cl键的离子性占44％,Zr-Cp键的共价性在84～93％之间.     

胺、醇、醚类化合物气相碱性的CNDO/2计算

用CNDO/2方法计算了近七十种含氮及含氧化合物的气相碱性。对脂肪胺、醇和醚,羰基化合物等系列,所得结果与实验值在次序上一致。讨论了这些化合物的气相碱性与分子中的电荷分布及电离势的关系。     

“Universal” CNDO/2 method (CNDO/2-U)

The Pople-Santry-Segal CNDO/2 method and the modified CNDO/2 version worked out recently by Clack for transition-metal complexes have been extended to the full periodic table.     

胰岛素分子主链构象的CNDO／2计算和比较

对蛋白质分子进行量子化学计算常采用如下方法:以肽基和残基侧链为基本计算单元,使对蛋白质分子的计算分解成各次单元的计算(图10)。计算时往往根据构象图选择代表点以减少工作量。例如,计算木瓜蛋白酶时,根据其构象图,212个肽基被分为10组,每组中选取1个代表点进行计算。用同样的方法处理残基侧链的计算。但该方法     

限制性自洽场开壳层CNDO/2方法

本文采用限制性自洽场CNDO/2方案,在IBM-PC/XT微机上实现了RHF的CNDO/2计算程序。计算了若干开壳层的小分子和含过渡金属的配合物, 得到体系总能量、电荷、键序、结合能, 与UHF的CNDO/2方法计算结果完全符合, 并且图象清晰·RHF的CNDO/2的方法的实现为半经验方法计算开壳层体系电子光谱跃迁强度, 磁超精细结构常数以及酉群的组态相互作用提供了一个好的波函数。     

CNDO/2 calculations of the interactions of formamide and imidazole: Another failure of CNDO/2

The interaction energy curve of the formamide-imidazole system resulting from the CNDO/2 method exhibits a superfluous minimum at a much smaller separation than the sum of the van der Waals radii of the closest atoms, and a low maximum at this latter distance. The relationship of the interaction energies using CNDO/2 and those using the atomic charges on the two molecules is investigated for this system.     

CNDO/2 study of benzene-chlorine complex

We have carried out CNDO/2 calculations for the benzene-chlorine complex in a number of configurations. In order to obtain reasonable complexation energies, it was necessary to exclude chlorine 3d-orbitals from the basis set. When onlys- andp-orbitals were included, we found maximum stability for the complex for an unsymmetrical geometry. The calculated complexation energy was ?3.5 kcal/mole. Configuration-interaction calculations predicted a wavelength of about 270 nm for the charge-transfer band. Most, but not all, geometries were found to produce stable complexes.     

CNDO/2 calculations of some polyazaindenes

The theoretically estimated dipole moments of indolizine, imidazo[1,2-a]pyridine, imidazo-[1,5-a]pyridine and of pyrazolo[ 1,5-a]pyridine obtained by the CNDO/2 approximation have been compared with the experimental values. The bond angles and bond distances for these polyazaindenes have been estimated.     

Treatment of hydrogen bonding within CNDO/2 and MINDO/3: CNDO/2H and MINDO/3H

A formalism has been developed to treat hydrogen-bonded A—H…?B systems within the CNDO /2 and the MINDO /3 methodologies. In this formalism the interactions are divided into three distinct classes; those between (a) two hydrogen-bonded atoms, (b) one hydrogen-bonded and non-hydrogen-bonded atom, and (c) two non-hydrogen-bonded atoms. The last class of interactions is treated solely by the existing CNDO /2 or MINDO /3 method. For A –H…?B systems, the core resonance integrals are individually parametrized depending upon the class of the interaction. Three types of A—H…?B systems have been thus far parametrized. Nine hydrogen-bonded dimers have been studied using the new formalism and the current CNDO /2 and the MINDO /3 methods. MINDO /3 predicts very large interatomic (A –B) distances for the equilibrium geometry, and relatively small stabilization values for the hydrogen-bond energies. CNDO/2 predicts the reverse. The new formalism for both CNDO /2 and MINDO /3 predicts accurate geometries as well as energies for all nine dimers. The new formalisms are called CNDO /2H and MINDO /3H. A general discussion of the nature of hydrogen bonding as exhibited by CNDO /2H and MINDO /3H is presented.     

Synthesis of Aromatic Polythioethers Containing 1,3,5-Triazine Ring by Aromatic Nucleophilic Substitution Polymerization

Abstract

Reaction of 2,4-dichloro-6-phenyl-1,3,5-triazines with bis(4-mercaptophenyl) sulfide in the presence of a base in THF afforded the corresponding condensation polymer as a whole aromatic polythioether in moderate yield. The polymerization of several 2,4-dichloro-1,3,5-triazine derivatives with this dithiols also proceeded in the o-dichlorobenzene-water two-phase system by using phase transfer catalysts. The resulting polymers consisted of THF-soluble and -insoluble fractions. The x-ray diffraction pattern indicated that these THF-insoluble polymers have a highly crystalline nature. Further, the polymers obtained here showed high thermal stability.     

A CNDO/2 calculation on stilbene

The equilibrium conformations of trans- and cis-stilbene and the rotational barrier between the two isomers were calculated using the CNDO/2 method. The results for the equilibrium angles and distances are in good agreement with experimental data. However, according to the calculations the phenyl rings would have a nearly free rotation which is only limited by steric hindrance. This result obviously deviates from the current view. The results are discussed in relation to previous theoretical and experimental evidence.

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Zusammenfassung Die Gleichgewichtskonformation von trans- und cis-Stilben und die Rotationsbarriere zwischen zwei Isomeren wurde nach der CNDO/2-Methode berechnet. Die Ergebnisse in bezug auf die Geometrie stimmen mit experimentellen Daten gut überein, die Rotationsbarriere für die Drehung der Phenylringe dagegen ist praktisch Null.

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Résumé La méthode CNDO/2 a été employée pour calculer les conformations d'équilibre du trans- et du cis-stilbène ainsi que la barrière de rotation entre ces deux isomères. Angles d'équilibre et distances calculés sont en bon accord avec les données expérimentales. Cependant les calculs indiquent que les cycles phényles devraient posséder une rotation libre soumise seulement à l'empêchement stérique. Ce résultat s'écarte de l'opinion courante. Les résultats sont discutés en relation avec les données théoriques et expérimentales antérieures.

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This work was supported by grant No 2741-4 from The Swedish Natural Science Research Council and grant No 69-927/U 697 from The Swedish Board for Technical Development.