硝酸酯分子几何构型的量子化学研究

运用MINDO / 3、MNDO 和AM1 三种半经验分子轨道(MO)方法, 通过SCF计算, 首次系统地获得了32个硝酸酯化合物分子的全优化几何构型。三种方法的计算结果与已报道的四个化合物(硝酸甲酯、吉纳、硝化甘油和太安)的实验结果相比, AM1法较好。所有硝酸酯的酯基(-ONO~2)具有近似不变的几何参数。直链烷基硝酸酯的键长和键角极为相近, 全部重原子均共平面。二元直链和四元硝酸酯具有对称的分子构型。     

多氰基立方烷生成热的DFT-B3LYP和半经验MO研究

运用密度泛函理论(DFT)B3LYP方法和半经验MO(MINDO/3,MNDO,AM1和PM3)方法系统计算了全部21种多氰基立方烷的生成热,首先,在DFT-B3LYP/6-31G^*水平下通过不破裂立方烷笼状骨架(亦即选择立方烷为参考物)的等键反应设计,精确计算了9种多氰基立方烷的生成热;发现B3LYP/6-31G^*结果分别地均与上述四种半经验MO方法求得的生成热之间存在良好的线性关系(相关系数均在0.9994以上),且以AM1生成热与B3LYP/6-31G^*计算值最为接近,其次,其它12种多氰基立方烷的精确生成热借助上述线性关系通过校正对应的AM1结果而获得,多氰基立方烷的生成热很高,且随-CN基数目的增加而线性地增大,表明它们属于极具潜力的“新一低高能炸药”而具开发价值。     

多氰基立方烷生成热的DFT-B3LYP和半经验MO研究

运用密度泛函理论(DFT)B3LYP方法和半经验MO(MINDO/3,MNDO,AM1和PM3)方法系统计算了全部21种多氰基立方烷的生成热,首先,在DFT-B3LYP/6-31G^*水平下通过不破裂立方烷笼状骨架(亦即选择立方烷为参考物)的等键反应设计,精确计算了9种多氰基立方烷的生成热;发现B3LYP/6-31G^*结果分别地均与上述四种半经验MO方法求得的生成热之间存在良好的线性关系(相关系数均在0.9994以上),且以AM1生成热与B3LYP/6-31G^*计算值最为接近,其次,其它12种多氰基立方烷的精确生成热借助上述线性关系通过校正对应的AM1结果而获得,多氰基立方烷的生成热很高,且随-CN基数目的增加而线性地增大,表明它们属于极具潜力的“新一低高能炸药”而具开发价值。     

金刚石(111)氢化表面脱氢势垒的量子化学研究

采用MNDO(UHF)方法,计算金刚石(111)面的脱氢势垒。在与气相有机分子脱氢活化能实验值系统比较的基础上,在一组尺度不同的金刚石表面团簇模型上进行了计算,结果收敛于42±4kJ/mol.并与MNDO(RHF)和AM1(UHF、RHF)方法给出的相应结果进行了比较。     

哌嗪二酮的气相Hel光电子能谱及其量化计算

给出了哌嗪二酮的气相HeI紫外光电子能谱(UPS), 并进行了化合物分子的HAM/3, MNDO, MINDO/3, INDO, CNDO/2和EHMO等量子化学计算研究. UPS谱低电离能(<11.00 eV)区的四重峰被指认为分子体系中氧-氧, 氮-氮原子孤对轨道间的通过键相互作用导致的分裂峰. 表明HAM/3和MNDO计算法是预指该化合物实验电离能正确次序、轨道对称性类型以及通过键相互作用导致分裂大小的较好方法.     

在不加对称性限制的条件下采用不同的半经验方法研究酞菁的电荷分布和几何构型（英文）

在不加对称性限制的条件下采用不同的半经验方法CNDO,INDO,MINDO/3,MNDO和Pm3对自由酞菁(H2Pc)进行几何构型最优化和电荷密度布居分析,并将所得结果与Am1方法以及X射线衍射和中子衍射数据的数据进行比较.结果表明只有从INDO方法得到的是桥式构型,而从CNDO, MINDO/3, MNDO,Am1, Pm3方法得到的都是键式构型.除INDO之外所有的这几种方法都对先前报道的几何构型扭曲给出进一步的支持证据.新近建立的半经验方法如MNDO,An1,Pm3等看起来更适合于用来研究大分子如酞菁及其类似物的几何构型扭曲和电荷分布极化等问题.     

在不加对称性限制的条件下采用不同的半经验方法研究酞菁的电荷分布和几何构型

在不加对称性限制的条件下采用不同的半经验方法CNDO,INDO,MINDO/3,MNDO和Pm3对自由酞菁(H₂Pc)进行几何构型最优化和电荷密度布居分析，并将所得结果与Am1方法以及X射线衍射和中子衍射数据的数据进行比较。结果表明只有从INDO方法得到的是桥式构型，而从CNDO,MINDO/3,MNDO,Am1,Pm3方法得到的都是键式构型。除INDO之外所有的这几种方法都对先前报道的几何构型扭曲给出进一步的支持证据。新近建立的半经验方法如MNDO,Am1,Pm3等看起来更适合于用     

多异氰基立方烷生成热的理论研究——高能量密度材料(HEDM)的寻求

运用密度泛函理论(DFT)B3LYP方法和半经验MO(MINDO/3, MNDO, AM1和PM3)方法系统计算了全部21种多异氰基立方烷的生成热. 首先, 在DFT-B3LYP/6- 31G*水平下通过不破裂立方烷笼状骨架(亦即选择立方烷为参考物)的等键反应设计, 精确计算了8种多异氰基立方烷的生成热; 发现B3LYP/6-31G*结果分别地均与上述4种半经验MO方法求得的生成热之间存在良好的线性关系(相关系数均在0.9971以上), 且以PM3法得到的生成热结果最好. 其次, 其他13种多异氰基立方烷的精确生成热借助上述线性关系通过校正对应的PM3结果而获得. 多异氰基立方烷的生成热很高, 且随—CN基数目的增加而线性地增大, 表明它们属于极具潜力的“新一代高能量密度材料(HEDM)”而具开发价值.     

环双(对-苯基-对草快)对中性客体的分子识别和分子开关

用 AM1及 MNDO方法对环双 (对 -苯基 -对草快 )与中性客体的配合物进行理论研究 ,得到稳定化能和配合物相互转换的 ΔΔE值 ;以 AM1优化构型为基础 ,用 INDO/ SCI方法计算 4种配合物光谱 ,并用AM1方法计算主体与二苯醚衍生物在 H+存在下的势能曲线 ,探讨分子开关形成机理 .     

核磁共振化学位移的MNDO/GIAO微扰法计算

本文首次应用MNDO近似和规范不变的原子轨道(GIAO)计算了化学位移,提出了MNDO/GIAO微扰计算法及单电子算符1/r_m,L_m及L_m/r_m~3的简单有效积分法.通过优化选择MNDO的β_μ参数,对一组典型有机分子~(13)C化学位移的计算结果表明,理论值与实验数据符合得很好,并克服了SOS微扰法对坐标原点的依赖性.     

Hydrocarbon acidities calculated with MINDO/3, MNDO,and AM1

Acidities of 32 hydrocarbons have been calculated using MINDO/3, MNDO, and AM1. All three semiempirical procedures have systematic errors and reproduce experimental acidities poorly. A linear correlation, however, does exist between the calculated and experimental results. Correction of the AM1 or MNDO acidities leads to good agreement with literature values even for acids, such as methane and ethylene, whose conjugate bases are small localized anions. Predictions for several hydrocarbons are given.     

Theoretical study of the proton affinities of 2-, 3-, and 4-monosubstituted pyridines in the gas phase by means of MINDO/3, MNDO,and AM1

Proton affinities (PAs) of 2-, 3-, and 4-monosubstituted pyridines in the gas phase are calculated using the MINDO/3, MNDO, and AM1 methods. The following substituents are considered: F, Cl, CN, CH₃, CF₃, CHO, NO₂, NH₂, N(CH₃)₂, OCH₃, and SCH₃. The results are compared with experimental values. It is found that all MINDO/3 PAs are ca. 6% too high (mean value) compared to the experimental results; on the other hand, the MNDO values are ca. 7% too low (mean value). However, a much better agreement has been observed for the AM1 method where the theoretical values are only ca. 2.4% too low (mean value). Correlations between the calculated proton affinities on one hand and the charges on the acid H atom and Hammett constants on the other hand are studied. Particularly good linear relationships are found for the 4-monosubstituted compounds within the AM1 formalism.     

A semiempirical and ab initio MO study of the tautomers ofN-unsubstituted pyrazolones [hydroxy pyrazoles]

Semiempirical (MNDOC, MINDO/3, AM1, and MNDO) and ab initio (STO-3G and 4-31G basis sets) calculations on the relative stabilities, structures, and dipole moments of the 8 theoretically possible tautomeric forms of pyrazolone are reported. It is shown that MNDO + CI and MINDO/3 predict that 5-hydroxy pyrazole, 3-hydroxy pyrazole, and 2-pyrazolin-5-on are the most stable. These results correspond to the known experimental data. Of all used quantum chemical methods, the MINDO/3 results for the dipole moments of the investigated tautomers are in best agreement with the known experimental data. The electronic excitation energies were calculated using the CNDO/S-CI method. The results are in good agreement with the experimental UV spectra.     

Enthalpy of formation of thiophene derivatives

The enthalpy of formation in the gas phase has been calculated for 21 carbonyl compounds of the thiophene series with the aid of the PM3, MINDO, AM1, and MNDO semiempirical quantum-chemical methods. Comparison of them with experimental data showed that the best linear correlation was achieved with the PM3 method. The latter in conjunction with a developed linear regression equation has been used to predict the enthalpy of formation of 22 carboxylic acids and ketones of the thiophene series.     

Comparison of semiempirical calculations for silicon compounds

A comparison is made of the performance of the MINDO/3, MNDO, AM1, and PM3 methods in calculating the nature of the dimer reconstruction observed on the silicon (100) crystal surface. Based on this case study we conclude that MINDO/3 gives the most realistic results, with PM3 calculations being quite similar but both MNDO and AM1 missing some key features of this system and giving rather unrealistic charge distributions. Hence use of PM3 is recommended for Si containing molecules where a lack of parameters or other restrictions prevent the use of MINDO/3.     

Enthalpies of formation of nitro-, nitroxy-, and nitrosoadamantanes

The enthalpies of formation of nitro-, nitroso-, and nitroxyadamantanes were calculated using semiempirical quantum-chemical PM3, MINDO, AM1, and MNDO methods incorporated into MOPAC software package. The best correlation with the experimental data was obtained with the results of PM3 calculations. Using the corresponding linear regression equation, the enthalpies of formation of 22 adamantane derivatives having nitro-, nitroso-, and nitroxy groups were calculated.     

Correlation of singlet-triplet gaps for aryl carbenes calculated by MINDO/3, MNDO,AM1, and PM3 with Hammett-type substituent constants

Heats of formation, atomic charges, and geometries of some 110 structures involving substituted singlet and triplet phenyl and 4,4-dimethyl-1,4-dihydronaphthalene carbenes and the corresponding diazomethanes were calculated by MINDO/3, MNDO, AM1, and PM3 semiempirical molecular orbital methods. The singlet-triplet gaps for AM1 and PM3 calculations for the para derivatives in both systems have been successfully correlated with Brown σ⁺ constants. Good correlations with σ⁺ were found for the charges on the carbenic centers of the singlets as well as with the energy barrier for rotation of the aryl group about the C-C single bond in substituted singlet phenylcarbenes. Comparisons of these results with experimental data indicate that AM1 and PM3 are much better than MNDO and MINDO/3 in predicting the intrinsic substituent effects in singlet carbenes.     

Calculations of molecular vibrational frequencies using semiempirical methods

MINDO/3, MNDO, AM1, and PM3 calculations of molecular vibrational frequencies are reported for 61 molecules. All techniques were applied to both well-behaved and badly behaved systems. Overall, MINDO/3 and MNDO were found to contain rather large errors whereas AM1 and PM3 were relatively accurate. Since no technique does well for all molecules, the technique used should be chosen based on the molecular vibration of interest. In general, AM1 and PM3 together provide fairly accurate results.     

Enthalpy of formation of adamantane alkyl derivatives

The enthalpies of formation of adamantane alkyl derivatives were calculated by the semiempirical quantum chemical methods PM3, MINDO, AM1 and MNDO of the MOPAC software package. Comparison of the calculated values with the experimental data showed that the best correlation gave the PM3 method. Using this method and linear regression equation derived by us we calculated enthalpies of formation of twenty-two alkyl derivatives of adamantane.     

Theoretical studies of [n]paracyclophanes and their valence isomers. I. Geometries,strain energies,and enthalpies of the inter-conversions of [n]paracyclophanes and their Dewar benzee isomers

Four semiempirical methods (AM1, MNDO, PM3, and MINDO/3) are used to calculate the deformation angles of [n]paracyclophanes and their Dewar benzene isomers for n = 3… 10. The results obtained by all these methods are in good agreement with data from X-ray studies. We have determined the strain energies that, in both series of compounds, are due to two components: (1) the strain energy of deformation of the cycle (aromatic or Dewar Benzene skeletons) and (2) the strain energy of the oligomethylene chain. In [6]paracyclophane, the strain energy [SE_ring(MNDO) ≈? 32.9 kcal/mol] almost compensates the resonance energy (E_resonance ≈ 36 kcal/mol) so that its chemical properties are closer to alkenes than to benzenic compounds. To better reproduce the enthalpy of the valence isomerization [n]Dewar bezene → [n]paracyclophane, which is poorly calculated with these methods, a correction is proposed and the reaction enthalpy of [6]paracyclophane is estimated to be about ΔH_r ≈ 15 ± 15 kcal/mol. It is found that MNDO and MINDO/3 need the smallest corrections, but MNDO leads to better geometries than MINDO/3. In conclusion, MNDO seems to be the best technique for further studies of these compounds. © 1992 by John Wiley & Sons, Inc.