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。     

C74(BN)2的UV和IR 光谱研究

Equilibrium geometries of 16 possible isomers for C74（BN）2 were studied by INDO series of methods, to indicate that the most stable three geometries are those where boron and nitrogen atoms substitute carbon atoms located at the same hexagon near the longest axis of C78 （C2v） to form B-N-B-N unit. Electronic spectra of C74（BN）2 were investigated with INDO/CIS method. The reason for the red shift of UV absorptions for C74（BN）2 compared with those of C78 （C2v） was discussed. IR spectra for 9,8,28,29-C74（BN）2 and 28,29,30,31-C74（BN）2 were calculated on the basis of AM1 geometries.     

Adsorption of the nitrosamine and thionitrosamine molecules as carcinogen compounds on the BN and B3Al N nanotubes: A DFT study

DFT calculations were performed to investigation of the influence of doping three atoms of aluminum on the electronic properties of the (4,0) zigzag boron nitride nanotube (BNNT). Also, adsorption properties of nitrosamine (NA) and thionitrosamine (TNA) molecules as carcinogen agents onto BN and B_Al3N nanotubes were studied. The results show that the B_3AlN nanotube is the most energetically favorable candidates for adsorption of these molecules. Also, B(B_3Al)NNT/TNA complexes are more stable than B(B_3Al)NNT/NA complexes. The HOMO–LUMO gap, electronic chemical potential (μ), hardness (?), softness (S), the maximum amount of electronic charge (ΔN_max) and electrophilicity index (ω) for monomers and complexes in the gas and polar solvent phases were calculated. The results show that the conductivity and reactivity of BNNT increase by doping Al atoms instead of B atoms. Also, the interaction of NA and TNA molecules with BN and B_Al3N nanotubes results in significant changes in the electronic properties of nanotubes. Based on the natural bond orbital (NBO) analysis, in all complexes charge transfer occurs from NA and TNA molecules to nanotubes. Theory of atoms in molecules (AIM) was applied to characterize the nature of interactions in nanotubes. It is predicted that, BN and B_3AlN nanotubes can be used to as sensor for detection of NA and TNA molecules.     

MNDO Calculations of silicon-containing molecules

A comparison is made of MNDO and MINDO /3 calculations for saturated silicon-containing molecules, and with experimental values, for heats of formation, molecular geometries, charge distributions, and ionization potentials. Except for bond angles, it is found that with the published parameter values the MINDO /3 program gives more reliable results than MNDO . For unsaturated molecules, a comparison of bond lengths and stabilities of Si multiple bonds as given by the two programs and ab initio methods is made, and large discrepancies between predicted structures are pointed out. Some reasons for the dicrepancies are discussed.     

Evaluation of MINDO/3 calculated structures. II. Branching errors in alkanes and cycloalkanes

MINDO/3 calculations have been carried out for a series of branched chain alkanes in order to assess effects of branching on calculated geometries and heats of formation (ΔH_f). With vicinal branching, MINDO/3 calculates the central C? C bond to be too long. Bond angles are also found to be distorted. Errors in calculated heats of formation are large when geminal branching is present and significant with vicinal branching. Branching error corrections for ΔH_f have been derived and applied to a separate series of branched acyclic and cyclic compounds. For the test sample, application of the branching error corrections gave calculated structures of acyclic branched hydrocarbons with heats of formation having an average absolute error of 1.3 kcal/mole rather than 17.3 kcal/mole before correction. Cyclic branched hydrocarbons are shown to be less well corrected. Calculations of heats of reaction have also been carried out for some isomerization and cyclization reactions using the MINDO/3 and MNDO methods. It is clear from the comparisons that MNDO calculations give less severe errors for highly branched compounds but the errors are still substantial. For prediction of heats of reaction, the error-corrected calculations are shown to be superior to the “raw” calculations obtained by MINDO/3 or MNDO.     

Synthesis,vibrational, and conformational properties of novel polyazadioxime chain molecules

Novel large polyazadioxime molecules 4,5,8,9-tetraaza-3,6,7,10-tetramethyl -3,5,7,9-dodecatetraene-2, 11-dione-2, 11-dioxime (H₂doxN₄) and 4,5,8,9,12, 13-hexaaza-3,6,7,10,11,14-hexamethyl-3, 5,7,9,11,13-hexadecahexane-2,15-dione-2, 15-dioxime (H₂doxN₆) were synthesized. The molecular geometries of these molecules as well as smaller dioxime molecules, H₂dox and H₂doxN₂ were optimized by using modified intermediate neglect of differential overlap (MNDO) calculations. The optimized conformations for all the molecules under study are close to the all-E, all-s trans conformation of C_2h symmetry group. However, the energy barriers of internal rotation around the N-N single bonds were found to be low. Therefore some distortions of the polyazabackbone through internal rotation the N-N bonds have been evidenced. By infrared and Raman spectroscopies in the solid state as well as in solution. From the MNDO calculations and vibrational spectroscopy, the polyaza chain molecules under study appear as a poorly conjugated system and can be represented as a sequence of single and double bond alternation.     

Density functional theory studies of effects of boron replacement on the structure and property of RDX and HMX

In this study, based on two model nitramine compounds hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5, 7-tetrazocine (HMX), two series of new energetic molecules were designed by replacing carbon atoms in the ring with different amounts of boron atoms, their structures and performances were investigated theoretically by the density functional theory method. The results showed that the boron replacement could affect the molecular shape and electronic structure of RDX and HMX greatly, and then would do harm to the main performance like the heat of formation, density, and sensitivity. However, the compound RDX-B2 is an exception; it was formed by replacing two boron atoms into the system of RDX and has the symmetric boat-like structure. Its oxygen balance (4.9%), density (1.91 g/cm³), detonation velocity (8.85 km/s), and detonation pressure (36.9 GPa) are all higher than RDX. Furthermore, RDX-B2 has shorter and stronger N NO₂ bonds than RDX, making it possesses lower sensitivity (45 cm) and better thermal stability (the bond dissociation energy for the N NO₂ bond is 204.7 kJ/mol) than RDX. Besides, RDX-B1 and HMX-B4 also have good overall performance; these three new molecules may be regarded as a new potential candidate for high energy density compounds.     

Molecular modeling of oxaphosphetane intermediates of wittig olefination reactions

The literature reveals that the structures of four unusual oxaphosphetanes have been established by x-ray diffraction studies, and the structure of one mythical oxaphosphetane ( 6 ) has been deduced by theoretical calculations. We have used these known structures to calibrate the MMX87 force field, the only necessary modification being the stretching term for the P-O bond. The bond length, 1_o, was set at 1.80Å, which is an “average” of the P-O axial bond distances of the stable oxaphosphetanes. The AMPAC (Ver. 1.0) molecular orbital package utilizing the MNDO hamiltonian was also applied to the same problem, starting with the minimized geometries of the modified MMX87 force field. Fixed bond lengths and full minimizations were performed. The computed geometries of the four-member ring of each of the four oxaphosphetanes of known structures were found to be in very good agreement with the values obtained by x-ray diffraction. Furthermore, the method was applied to the mythical oxaphosphetane, and the results of MMX87 and MNDO calculations were found to be in very good agreement with the results of ab initio calculations. The MMX force field and the MNDO semiempirical method have been used to calculate the geometries and the steric energies (or heats of formation) of diastereomeric oxaphosphetanes formed in a theoretically real Wittig reaction.     

异质富勒烯C76BN的UV和IR光谱研究

Twenty-tow possible isomers for C76BN were studied by INDO methods. The two most stable geometries are 52,53-C76BN and 29,28-C76BN, in which boron and nitrogen atoms are connected with each other and located at the 6/6 bond near the longest axis of C78(C2v). Electronic spectra of C76BN were investigated with INDO/SCI method. UV absorptions of C76BN are red-shifted compared with those of C78(C2v). The structures and IR spectra for the four stable isomers of C76BN were calculated by AM1 method. It was indicated that the substitution of the BN unit weakens the conjugation of carbon atoms, leading to the decrease of IR frequencies.     

A study of hydration effects on the conformational aspects of gaba mediators

The conformation of numerous chemical compounds is strongly influenced by solvents. Knowledge of their structure in solution is necessary, especially for a discussion of the biological and pharmacological activity of the molecules. The neurotransmitters and their agonists and antagonists are known to be flexible molecules that interact with quite distinct receptors. The conformational properties of several GABA (γ-aminobutyric acid) mediators have been studied by the MNDO technique. The optimized geometries of the molecules have been used to study the solvent effects on their conformational properties considering the supermolecule approach for their first hydration shell. A conjectural pharmacophoric pattern for several GABA inhibitors has already been suggested from the molecular electrostatic potentials (MEP ) of several molecules using a localized bond orbital technique. In the present work, MEP calculations have been carried out considering a solvent effect on the MNDO optimized geometries to investigate any deviation from the earlier results.     

Covalent attachments of boron nitride nanotubes through a carboxylic linker: Density functional studies

Properties of attached boron nitride (BN) nanotubes based on linking two zigzag nanotubes through a carboxylic (–(CO)O–) linker were investigated by performing density functional theory (DFT) calculations. The linking boron and nitrogen atoms at the edges of two zigzag BN nanotubes were linked to the –(C]O)O– linker to make possible the attachments of two BN nanotubes together. Total energies, energy gaps, dipole moments, linking bond lengths and angles, and quadrupole coupling constants were obtained for the optimized structures to determine the properties of the attached BN nanotubes. The results indicated that different properties could be seen for the investigated models based on their linking status. For quadrupole coupling constants, the most significant changes of parameters were observed for the linking atoms among the investigated models of attached BN nanotubes.     

An ab initio study of the relative stabilities of the isomers of CH2N2 and SiH2N2

Ab initio SCF calculations of the equilibrium geometries have been carried out on nine possible isomers of MH₂N₂, where M = C or Si, and compared with the results of MNDO calculations. The results for the carbon compounds are in good agreement with available experimental data, but in the case of the silicon compounds, the molecules are predicted to be unstable with respect to decomposition to SiH₂ and N₂. The inclusion of electron correlation at the MP3 level does not alter the order of the relative stabilities, although the importance of the correlation contribution varies substantially between the different isomers.     

A density functional treatment of organolithium compounds: Comparison to ab initio,semiempirical, and experimental results

Density functional calculations on several classes of organolithium compounds are described. The compounds studied include lithium bonds to carbon, oxygen, and nitrogen and are representative of most types of organolithium compounds that have appeared in the recent literature. The computational results are compared to those using MNDO, which has been shown to have some serious deficiencies in compounds involving carbon–lithium bonds, and to PM3 results, which offer some improvement over MNDO for many organolithium compounds. Most of the density functional calculations with a large basis set are in good agreement with available ab initio and experimental data. Calculated carbon–lithium bond lengths were slightly shorter than those calculated by other ab initio methods and were substantially longer than those calculated by MNDO, which is known to underestimate carbon–lithium bond lengths severely. Dimerization energies of methyllithium, calculated by DMol, were also in good agreement with those of other ab initio calculations. Lithium–nitrogen bonds in lithium amides were calculated to be slightly shorter by DMol than by MNDO, although the two methods were in qualitative agreement for this type of compound. © 1995 by John Wiley & Sons, Inc.     

Spectres de vibration des molecules BCl2CO et BX2NCS (X = Cl,Br, I), champs de forces et modes normaux

Experimental data on the vibrational spectra of BX₂¹⁴NCS (X = Cl, Br or I), BCl₂¹⁵NCS, BBr₂¹⁵NCS, and BCl₂NCO are reported. Analysis of the results shows that the boron atom is bonded to the nitrogen atom, and the BN, CN, CS and CO bonds are colinear. Force fields are calculated and found to reproduce the experimental frequencies and the ¹⁰B-¹¹B and ₁₄N-₁₅N isotopic effects. High values are obtained for the force constant of the B-N stretching vibration (about 6.5 mdyn Å^?1) and it is shown that, owing to electron transfer from nitrogen to boron, the B-N bond is intermediate between a single and a double bond. The force constant νBX is marginally greater than that for the corresponding BX₂SH compounds. The C-N bond is weaker than in the NCS ion, whereas the CS bond is stronger.Calculation of the normal modes and the potential energy distribution shows that for the BCl₂NCO molecule, the B, N, C, and O atoms are almost equally involved in all the modes of A, symmetry, especially those at 2270, 1525 and 1022 cm^?1. On the other hand, for BX₂NCS compounds, the potential energy is relatively localised on one coordinate. Consequently, the group vibration approximation is justified in this case.     

CO-Induced Dinitrogen Fixation and Cleavage Mediated by Boron

The boron atoms react with carbon monoxide and dinitrogen forming the end-on bonded NNBCO complex in solid neon or in nitrogen matrices. The NNBCO complex rearranges to the (η²-N₂)BCO isomer with a more activated side-on bonded dinitrogen ligand upon visible light excitation. (η²-N₂)BCO and its weakly CO-coordinated complexes further isomerize to the NBNCO and B(NCO)₂ molecules with N−N bond being completely cleaved under UV light irradiation. The geometries, energies and vibrational spectra of the molecules are calculated with quantum chemical methods and the electronic structures are analyzed with charge- and energy-partitioning methods.     

富勒烯C_(36)等电子体C_(34)BN异构体的结构及其相对稳定性理论研究

用半经验的AM1和MNDO方法优化了富勒烯C_(36)的等电子体C_(34)BN所有可能 异构体的构型,分析了各异构体相对稳定性与杂原子取代位置间的关系。另外,比 较了C_(36)碳笼上同位置地取代杂原子形成的C_34BN,C_(34)B_2和C_(34)N_2间的 电子结构,并分析了C_(34)BN最稳定异构体的振动模型。结果表明以C_(36):A (D_(6h))为母体形成的最稳定C_(34)BN异构体对应于碳笼赤道位置六元环中1,4- 取代产物,而以C_(36):B(D_(2d))为母体形成的最稳定C_(34)BN异构体对应于碳笼 近赤道位置的1,2-取代产物.C_(34)BN各异构体的稳定性可能主要由体系的共轭性 质决定。前线轨道能级表明B,N原子取代所得异构体的氧化-还原活性按以下顺序 递增：C_(34)B_2相似文献   

Pyrrolizidine alkaloids necine bases: Ab initio,semiempirical, and molecular mechanics approaches to molecular properties

The structural stabilities of endo and exo conformations of retronecine and heliotridine molecules were analyzed using different ab initio, semiempirical, and molecular mechanics methods. All electron and pseudopotential ab initio calculations at the Hartree-Fock level of theory with 6-31G* and CEP-31G* basis sets provided structures in excellent agreement with available experimental results obtained from X-ray crystal structure and ¹H-NMR (nuclear magnetic resonance) studies in D₂O solutions. The exo conformations showed a greater stability for both molecules. The most significant difference between the calculations was found in the ring planarity of heliotridine, whose distortion was associated with the interaction between the O(11)H group and the C(1)-C(2) double bond as well as with a hydrogen bond between O(11)H and N(4). The discrepancy between pseudopotential and all-electron optimized geometries was reduced after inclusion of the innermost electrons of C(1), C(2), and N(4) in the core potential calculation. The MNDO, AM1, and PM3 semiempirical results showed poor agreement with experimental data. The five-membered rings were observed to be planar for AM1 and MNDO calculations. The PM3 calculations for exo-retronecine showed a greater stability than the endo conformer, in agreement with ab initio results. A good agreement was observed between MM3 and ab initio geometries, with small differences probably due to hydrogen bonds. While exo-retronecine was calculated to be more stable than the endo conformer, the MM3 calculations suggested that endo-heliotridine was slightly more stable than the exo form. © 1996 by John Wiley & Sons, Inc.     

The Clar Structure in Inorganic BN Analogues of Polybenzenoid Hydrocarbons: Does it Exist or Not?

The Clar structure of polybenzenoid hydrocarbons (PBHs) have attracted considerable interest of both theoretical and experimental chemists since it was proposed in the 1950s. However, it remains unclear whether the Clar structure could exist in inorganic PBHs, the boron nitride (BN) analogues where the alternate boron and nitrogen atoms are used to replace the carbon atoms of PBHs. Here, we carry out thorough density functional theory (DFT) calculations to probe the possibility of Clar structures in BN analogues of PBHs. A strong correlation (r²=0.975) between the ring number (n=3–10) of BN analogues of [n]acenes and energy differences between the most and least stable isomers is identified, suggesting the existence of Clar structures in inorganic PBHs. In addition, the slightly weaker correlations in comparison to that (r²=0.989) of the organic PBHs is rationalized by the reduced aromaticity, which is revealed by two aromatic indices: ELF_π and SCI.     

13C?1H coupling constants in 9, 10-dihydroanthracene

The ¹H and ¹³C NMR spectra of 9,10-dihydroanthracene have been obtained at 2.1 and 9.4 T using selective decoupling of the methylene protons. Complete spectral analyses of the experimental spectra have provided the chemical shifts and coupling constants. The ¹³C? ¹H coupling constants in 9, 10-dihydroanthracene and biphenylene have been well accounted for by MNDO theoretical calculations of the molecular geometries and bond orders in these compounds.