硝酸酯化合物生成热的分子轨道研究

用MINDO/3, MNDO和AM1三种SCF-MO方法, 在全优化分子几何构型的基础上, 系统地计算研究了32个硝酸酯化合物的生成热, 与实验值相比, MNDO计算结果偏大很多; MINDO/3计算值与凝聚相实验值符合较好, 由于克服了MNDO法过高地估算原子之间Van der Waals核排斥能的缺点, AM1法给出了较满意的结果: 与七个气态实验值之间存在良好的线性关系(相关系数为0.992), 其间的平均绝对差值和平均差值分别只有10.28和-1.01kJ/mol。     

硝酸酯几何构型、生成热和电子结构的PM3 研究

用PM3 SCF-MO方法,通过能量梯度全优化计算,得到39个硝酸酯化合物的分子几何构型、生成热和电子结构。与实验结果和AM₁计算结果进行了比较和评估。     

硝酸酯几何构型,生成热和电子结构的PM3研究

用ＰＭ３ ＳＣＦ－ＭＯ方法，通过能量梯度全优化计算，得到３９个硝酸酯化合物的分子几何构型、生成热和电子结构。与实验结果和ＡＭ１计算结果进行了比较和评估。     

硝酸酯类分子力学参数的确定和应用

运用MM2(85年版)分子力学程序, 以硝酸甲酯、硝酸乙酯的实验结构为参比, 调试确定了硝酸酯类化合物的伸缩力常数(K~s)、弯曲力常数(K~b)和旋转力常数(V~1、V~2、和V~3)。用这套力场参数计算了硝酸甲酯、硝酸乙酯和硝化甘油的平衡几何构型、生成热和偶极矩, 计算结果与实验值和从头计算结果相一致。还用这套参数计算了结构未见报道的异基硝酸酯、丙烯基硝酸酯和苯基硝酸酯, 所得结果与MNDO全优化几何构型相符。     

三氟甲基侧取代氧、氮、硫杂大环化合物的合成和 分子结构

合成了四个三氟甲基侧取代氧、氮、硫杂大环化合物,通过IR、^1HNMR、RS和元素分析作了表征;用AM1方法计算它们的电子结构,并根据计算结果给出了它们的几何构型。     

三氟甲基侧取代氧、氮、硫杂大环化合物的合成和分子结构

合成了四个三氟甲基侧取代氧、氮、硫杂大环化合物,通过IR、~1H NMR、MS和元素分析作了表征;用AM1方法计算它们的电子结构,并根据计算结果给出了它们的几何构型。     

N,N-二(N-亚甲基-2-吡咯烷酮)丙氨酸(C13H21N3O4)的结构和配位性能

N,N二 (N亚甲基 2吡咯烷酮 )丙氨酸是我们最近合成的一个新化合物（如图 1所示）,经 X射线衍射实验测定了它的晶体结构,得到了其结构数据。实验结果表明它与稀土离子及其邻菲咯啉形成的配合物具有光致变色的性能。针对该柔性分子具有较复杂的三维构型结构, 为了更好地研究该化合物与金属离子的配位性能,我们基于量子化学 AM1方法的计算结果,从标题化合物分子的几何构型、能量特性、电荷布居、前线分子轨道特征等方面研究了该化合物的配位性能,并与实验进行了比较。 1计算方法 本文根据常见的键长键角数据作为初始化参数…     

PETN基PBX结合能和力学性能的理论研究

PETN(季戊四醇四硝酸酯)是著名的硝酸酯类猛炸药,用量子力学(QM)、分子力学(MM)和分子动力学(MD)方法,计算模拟其与高聚物组成的PBX(高聚物粘结炸药)的结合能和力学性能.以AM1-MO法和MM方法取PETN与系列高聚物的尺寸匹配原子簇模型,经几何全优化计算,发现两种方法求得的结合能彼此线性相关.对PETN超晶胞及其与系列氟聚物组成的双组分PBX,实施COMPASS力场下的分子动力学(MD)周期性模拟,求得其弹性系数、拉伸模量、体模量、剪切模量和泊松比,发现添加少量高聚物确能有效改善炸药的力学性能.     

两个三(邻溴苄基)锡羧酸酯的合成、结构及抗肿瘤活性

合成了2个有机锡羧酸酯化合物三(邻溴苄基)锡噻吩2-甲酸酯(1)和三(邻溴苄基)锡肉桂酸酯(2).通过元素分析、红外光谱、核磁共振谱(1H、13C和119Sn)、差热分析、X射线单晶衍射方法对1和2进行了结构表征,对其结构进行了量子化学从头计算.结果 显示,化合物1和2均为单锡核结构,锡原子均为四配位的畸变四面体构型....     

痂囊腔菌素A分子构型和分子内氢键的理论研究

用半经验量子化学AM1方法对天然苝醌化合物痂囊腔菌素A(EA)的分子构型和分子内氢键进行了研究;从EA可能的64种构型中选择16种进行了计算.结果表明,EA的X射线晶体结构对应的构型是II型左旋(A)a,a型(II-L-A-a,a);小的生成热差值可以使得异构体间的转换容易进行,有利于发生分子内质子传递.尽管采用AM1方法计算得到的EA各种构象的平面性有所差别,但都很接近晶体的平面性.此外,EA分子内氢键键能的平均值为22.9kJ/mol;II型的氢键键能比I型的大,(9,10)位的氢键键能比(3,4)位的大;EA的平面性是由苝醌环上的侧链取代所决定,而与分子内是否存在氢键无关.     

Calculation of fully optimized geometries of five- and six-membered heterocycles by the CNDO force method

Equilibrium geometries of five- and six-membered aromatic molecules have been calculated by applying the force method of the CNDO/2 procedure. The calculated and experimental geometries agree surprisingly well. The reliable values obtained for bond angles are of special importance in calculating molecular conformations.     

How accurate are TD-DFT excited-state geometries compared to DFT ground-state geometries?

In this work, we take a different angle to the benchmarking of time-dependent density functional theory (TD-DFT) for the calculation of excited-state geometries by extensively assessing how accurate such geometries are compared to ground-state geometries calculated with ordinary DFT. To this end, we consider 20 medium-sized aromatic organic compounds whose lowest singlet excited states are ideally suited for TD-DFT modeling and are very well described by the approximate coupled-cluster singles and doubles (CC2) method, and then use this method and six different density functionals (BP86, B3LYP, PBE0, M06-2X, CAM-B3LYP, and ωB97XD) to optimize the corresponding ground- and excited-state geometries. The results show that although each hybrid functional reproduces the CC2 excited-state bond lengths very satisfactorily, achieving an overall root mean square error of 0.011 Å for all 336 bonds in the 20 molecules, these errors are distinctly larger than those of only 0.004–0.006 Å with which the hybrid functionals reproduce the CC2 ground-state bond lengths. Furthermore, for each functional employed, the variation in the error relative to CC2 between different molecules is found to be much larger (by at least a factor of 3) for the excited-state geometries than for the ground-state geometries, despite the fact that the molecules/states under investigation have rather uniform chemical and spectroscopic character. Overall, the study finds that even in favorable circumstances, TD-DFT excited-state geometries appear intrinsically and comparatively less accurate than DFT ground-state ones.     

How to Predict Excited State Geometry by Using Empirical Parameters Obtained from Franck-Condon Analysis of Optical Spectrum

Excited state geometries of molecules can be calculated with highly reliable wavefunction schemes. Most of such schemes, however, are applicable to small molecules and can hardly be viewed as error-free for excited state geometries. In this study, a theoretical approach is presented in which the excited state geometries of molecules can be predicted by using vibrationally resolved experimental absorption spectrum in combination with the theoretical modelling of vibrational pattern based on Franck-Condon approximation. Huang-Rhys factors have been empirically determined and used as input for revealing the structural changes occurring between the ground and the excited state geometries upon photoexcitation. Naphthalene molecule has been chosen as a test case to show the robustness of the proposed theoretical approach. Predicted 1B_2u excited state geometry of the naphthalene has similar but slightly different bond length alternation pattern when compared with the geometries calculated with CIS, B3LYP, and CC2 methods. Excited state geometries of perylene and pyrene molecules are also determined with the presented theoretical approach. This powerful method can be applied to other molecules and specifically to relatively large molecules rather easily as long as vibrationally resolved experimental spectra are available to use.     

炸药敏化剂的分子结构、电子结构和生成热的理论研究

在HF/6-31G*和B3LYP/6-31G*基组水平上, 对硝酸乙酯(EN)、硝酸正丙酯(NPN)、硝酸异丙酯(IPN)、硝酸异辛酯(EHN)和四甘醇二硝酸酯(TEGDN)五种炸药敏化剂进行理论计算, 研究了标题物的分子结构、电子结构和能量等方面的性质. 基于Mulliken布居和键长分析, 五种硝酸酯分子的热分解始于O2—N3键的断裂, 且由Mulliken电荷分布推知分子热解产生NO2气体. 在分析前线轨道能(EHOMO, ELUMO)和能量差(ΔE)的基础上对五种硝酸酯的相对热稳定性大小进行了评估. 由等键反应获得的EN、IPN、NPN、EHN和TEGDN的标准生成热分别是-155.972、-190.896、-175.279、-272.376和-790.733 kJ·mol-1.     

A crystallographic, EPR and theoretical study of the Jahn-Teller distortion in [CuTp2] (Tp- = tris[pyrazol-1-yl]hydridoborate)

Crystals of the title compound (1) contain two independent, centrosymmetric half-molecules per asymmetric unit. While both of these show Jahn-Teller elongated six-coordinate geometries, the lengths of the elongated Cu-N bonds in the two molecules differ by 0.117(2) A at 30 K. The structure of one of these molecules (molecule A) does not vary with temperature below 350 K. The other molecule (molecule B) shows Cu-N bond lengths that are temperature-dependent between 225 and 375 K, but do not vary further at lower temperature. This indicates a fluxional axis of Jahn-Teller elongation in this molecule at these higher temperatures. Consideration of the thermal parameters in these structures implies that the fluxionality in molecule B is frozen out near 150 K. This conclusion is supported by a Q-band powder EPR study. The d-d transition energies of molecules A and B have been calculated by several density function (DF) methods, including a time-dependent DF calculation. The crystallographic data have been reproduced using the vibronic coupling model of Burgi and Hitchman. This has shown that the different fluxionality regimes for molecules A and B are not a consequence of their different static molecular structures, but rather reflect their different local environments in the crystal.     

吩噻嗪、N-甲基吩噻嗪及其自由基正离子的结构和电子光谱的理论研究

用INDO系列方法对吩噻嗪、N-甲基吩噻嗪及其自由基正离子进行了几何构型优化, 中性分子为蝶状折叠形, 自由基正离子为平面构型。以优化构型为基础,计算了上述四种分子、离子的电荷密度、自旋密度、键序和电子光谱, 对光谱进行理论指认的同时, 讨论了从中性分子到离子谱带红移的原因。所有理论计算值均与实验值一致。     

Hydrogen Bond Cooperativity and the Three‐Dimensional Structures of Water Nonamers and Decamers

Broadband rotational spectroscopy of water clusters produced in a pulsed molecular jet expansion has been used to determine the oxygen atom geometry in three isomers of the nonamer and two isomers of the decamer. The isomers for each cluster size have the same nominal geometry but differ in the arrangement of their hydrogen bond networks. The nearest neighbor O? O distances show a characteristic pattern for each hydrogen bond network isomer that is caused by three‐body effects that produce cooperative hydrogen bonding. The observed structures are the lowest energy cluster geometries identified by quantum chemistry and the experimental and theoretical O? O distances are in good agreement. The cooperativity effects revealed by the hydrogen bond O? O distance variations are shown to be consistent with a simple model for hydrogen bonding in water that takes into account the cooperative and anticooperative bonding effects of nearby water molecules.     

Similarity transformation of the ab initio density matrix

Bond orders and hybrid populations have been calculated from the density matrix localized in molecular space using similarity transformation for some fluorobenzene with the minimal basis set using Gaussian series of program. The ab initio bond orders and hybrid populations have been compared with the semiempirical calculations on this set of molecules. Also, these bond orders have been used in Coulson's bond order-bond length relationship to estimate bond lengths. The present calculations suggest that the qualitative predictions of molecular geometries are possible from these bond orders.     

含S-P-N键的磷烯正离子及其相关物的结构和性质的从头计算

本文对5-甲硫基-3-N-苯基-2,3-2(H)-1,3,4,2-噻二唑磷茂啉的磷烯正离子等三个相关分子的平衡几何构型进行了从头算解析能量梯度方法的全优化计算. 优化结果表明, 二配位磷烯正离子与相应的三配位磷母体分子的结构有本质的差异.形成二配位磷烯正离子后,磷所在的五员环形成共轭体系而使原来的单键键长变短, 原来的双键键长变长, 且使原来不共面的五员环共面. 在优化的平衡几何处进行单点CI计算的结果表明, 基态分子中磷原子上的正电荷的相对多少次序与实验测得的摩尔电导率及^3^1P NMR谱的化学位移的相对大小次序完全一致.     

Restricted geometry optimization: a different way to estimate stabilization energies for aromatic molecules of various types

At RHF, MPn, and DFT levels, a procedure of geometry optimization under the restrictions of pi-orbital interactions (GOR) was developed, thus providing a conjugated molecule with the following two types of localized reference geometries: a "GL" geometry where all double bonds are localized, and n different "GE-n" geometries, in each of which only two double bonds were permitted to conjugate. Interestingly, the molecular energy differences between the corresponding pairs of GE-n and GL geometries were found to be additive in each of the acyclic polyenes, and these were not additive for benzene. As a result, an extra stabilization energy (ESE) value of -39.0 kcal/mol was found in benzene. Afterward, GOR was applied to benzene- and furan-like species, strained aromatic molecules, and substituted benzenes, and the calculated ESEs for these molecules were found to be in reasonable ranges. The GOR can isolate a specific group from other groups, and it has several special functions. First, with regard to the substituent effect, the ESE difference between substituted benzene and benzene can be partitioned into conjugative and inductive parts. Second, the behavior of strained aromatic molecules can be ascertained from the roles of their resonance interactions, strained-induced bond localization (SIBL), and inductive effects, indicating that it is resonance interactions, rather than SIBL, which are responsible for localizing double bonds. Emphatically, it is the GL and GE-n geometries of aromatic molecules, rather than nonaromatic compounds, which can be used as the reference structures for calculating ESE. Particularly, these localized geometries are no longer arbitrary.