Substituent Effect on Infrared Spectra and Thermodynamic Properties of Polynitroamino Substituted Cyclopentane and Cyclohexane

运用密度泛函理论方法计算并研究了多硝基氮杂取代环戊烷和环己烷中的取代基效应. 基于B3LYP/6-31G**水平优化的分子结构,通过简谐振动分析,求得两类单环硝胺的红外光谱并作归属,发现理论计算值与已有实验值吻合较好. 基于统计热力学原理,求得它们的热力学性质,探讨了热力学性质与温度和取代基数目之间的关系. 结果表明,热力学性质与温度变化和取代基数目之间均很好地线性相关,同时取代基数目对热力学性质的变化具有基团加和性     

药物小分子化学位移的量子化学计算研究

核磁共振的谱峰归属对分子结构的确定至关重要,用理论计算方法预测化学位移对谱峰的正确归属是极其有帮助的. 我们用量子化学的方法预测了乙酰水杨酸及其衍生物分子上碳原子的化学位移,并通过比较计算值和实验值得到不同理论计算方法的误差范围. 用HF和DFT理论计算芳环碳的化学位移时,CSGT方法比GIAO方法更为准确. 与其它方法相比,B3PW91//CSGT 在6-311G(d,p)基组下得到的芳环碳的化学位移最接近实验值. 采用B3LYP//GIAO计算时, 使用不同的基组 6-31G(d,p)和6-311++G(3df,3pd)得到的化学位移计算值只有δ 0.01~2.04的差异. MP2方法非常耗时,且对于计算精度的改善并不显著; 并且,由于电子相关性的影响,碳原子周围的电子环境对化学位移计算的准确性影响很大. 与实验值比较,HF方法由于忽略电子相关效应所以表现较差. 另外,碳链的增长对计算准确性也存在一定影响.      

几种香豆素衍生物核磁共振谱的理论研究

在B3LYP / 6-311G(d,p)水平下对六种香豆素衍生物的结构进行了优化,并通过振动分析验证了其稳定性。利用GIAO方法在B3LYP/6-311G(d,p)水平下研究了香豆素衍生物的NMR谱。研究表明,六个化合物结构共平面性较好,具有较大共轭体系;不同的取代基和取代基的不同位置对几种香豆素衍生物的NMR都有不同的影响。苯环上的氢原子被其他基团取代后,其α-C原子和邻位碳原子的δ值变化明显,而间位碳原子δ值几乎没有变化。取代基的电负性对α-C原子δ值的影响具有一定规律性,而共轭效应对苯环碳原子的影响则更为复杂。最后,为了说明理论计算值与实验值之间的相关性,给出了六种衍生物化学位移值的理论与实验值相关图,并进行线性回归。结果表明,六种香豆素衍生物的化学位移理论与实验值之间的相关性非常好。     

几种香豆素衍生物核磁共振谱的理论研究（英文）

在B3LYP/6-311G(d,p)水平下对六种香豆素衍生物的结构进行了优化,并通过振动分析验证了其稳定性。利用GIAO方法在B3LYP/6-311G(d,p)水平下研究了香豆素衍生物的NMR谱。研究表明,六个化合物结构共平面性较好,具有较大共轭体系;不同的取代基和取代基的不同位置对几种香豆素衍生物的NMR都有不同的影响。苯环上的氢原子被其他基团取代后,其α-C原子和邻位碳原子的δ值变化明显,而间位碳原子δ值几乎没有变化。取代基的电负性对α-C原子δ值的影响具有一定规律性,而共轭效应对苯环碳原子的影响则更为复杂。最后,为了说明理论计算值与实验值之间的相关性,给出了六种衍生物化学位移值的理论与实验值相关图,并进行线性回归。结果表明,六种香豆素衍生物的化学位移理论与实验值之间的相关性非常好。     

骨显像放射性药物锝-双膦酸盐配合物99mTc-MDP的结构

运用密度泛函理论方法对锝标记双膦酸盐配合物^99mTc-MDP进行了结构预测和计算, 其中MDP代表亚甲基双膦酸. 根据几何异构、构象异构、电荷异构和自旋态异构等特性预测该化合物共有14种异构体. 基于B3LYP/LANL2DZ水平优化的分子结构和计算的总能量,确定了两种稳定异构体,并与实验结构进行了比较. 运用B3LYP/6-31G*(LANL2DZ用于Tc, cc-pVDZ-pp用于Tc)和B3LYP/DGDZVP方法对化合物的稳定结构进行了计算. 理论计算值与实验值吻合较好,而基     

3种黄酮醇类化合物核磁共振碳谱的理论研究

在B3LYP/6-31G水平下优化了3种黄酮醇类（山奈酚,槲皮素,杨梅素）化合物的几何构型. 在振动分析中,均未出现虚频率. 在B3LYP/6-31G的水平下计算了该类化合物的核磁共振碳谱. 研究结果表明：3种分子均有分子内氢键形成,且分子内氢键的键长为0.17~0.18 nm左右 . 本文讨论了羟基引入之后对邻近C的化学位移的影响. 从取代基对NMR的影响来看,随着取代基对苯环的供电子能力的加强,取代基邻近的一些C的化学位移有所改变.      

几种N-取代-3-羟基-2-吡啶硫酮Be配合物的结构与光谱性质

在B3LYP/6-31+G(d)级别水平上对4种Be配合物的几何结构进行了全优化,并探讨了烷基取代基对其分子的几何结构和电子结构等方面的影响.采用TD-B3LYP方法在同样级别水平上研究了各配合物的电子吸收光谱,分析了光谱的变化规律.上述计算结果表明,随烷基取代基团给电子能力的增强,前线分子轨道能级升高、能隙增大、最大吸收波长发生蓝移,且最大吸收波长的跃迁类型为配体内的π→π*跃迁.     

Ab initio Study on Structures and Isomerization of Magnesium Fluorosilylenoid H2SiFMgF

采用从头算分子轨道理论对镁氟类硅烯H2SiFMgF的构型及异构化进行了研究. 在B3LYP/6-31G(d,p)和G3MP2B3水平上找出四种构型及三种过渡态,并进行了全优化. 在B3LYP/6-31G(d,p)的优化参数基础上,得到了各构型的振动频率,计算了e29Si的化学位移.在B3LYP/6-31G(d,p)水平上,以四氢呋喃为溶剂,采用可极化连续模型研究了溶剂化效应. 并采用内察反应坐标方法对过渡态进行了验证. 研究结果表明,四面体结构具有最低的能量,最稳定. 四面体、三元环和p-络合物结构为实验可探测结构,σ-络合物结构具有最高能量,也是不能存在的构型     

几种N-取代-3-羟基-2-吡啶硫酮Be配合物的结构与光谱性质

在B3LYP/6-31+G(d)级别水平上对4种Be配合物的几何结构进行了全优化,并探讨了烷基取代基对其分子的几何结构和电子结构等方面的影响。采用TD-B3LYP方法在同样级别水平上研究了各配合物的电子吸收光谱,分析了光谱的变化规律。上述计算结果表明,随烷基取代基团给电子能力的增强,前线分子轨道能级升高、能隙增大、最大吸收波长发生蓝移,且最大吸收波长的跃迁类型为配体内的π→π*跃迁.     

两种含硅炔基树脂的固化行为研究

综合采用红外光谱（FTIR）、核磁碳谱 (13C NMR)、差示扫描量热（DSC）,热失重测试(TGA)等多种表征手段,研究了聚硅芳炔（PAR）和聚硅乙炔（PMR）两种含硅炔基树脂的固化行为,讨论了树脂固化物的结构与热稳定性的关系。结果表明：PAR和PMR树脂的固化机理不同,PAR主要通过炔基间的加成和Diels-Alder反应实现分子间的固化交联,并最终形成由苯环和稠芳环组成的芳构网络;PMR则主要通过硅氢基、炔基、烯基之间的加成反应实现固化,并成形饱和的碳硅Si—C(sp3)网络结构。固化成型的芳构网络和Si—C(sp3)网络结构分别赋予了PAR和PMR树脂固化物良好的热稳定性能,它们的热分解温度T_d5均大于600 ℃,900 ℃残重率均达到85%以上。     

Theoretical Studies on Electronic Structures and Spectroscopy of Fluorescent Arylamino Fumaronitrile

设计了一系列发荧光的芳胺氰化物, 并用密度泛函方法在B3LYP/6-31G*水平上进行几何构型优化．在优化构型基础上,分别用INDO/CIS、AM1、CIS-ZINDO TD和B3LYP/6-31G*方法计算了芳胺氰化物的电子光谱、红外光谱、荧光光谱及核磁共振碳谱．结果表明,与母体相比,由于萘环较大的立体效应使氰化物的能隙变宽,荧光光谱及电子光谱的主要吸收峰发生蓝移．而由于电子被分散到萘环上,氰化物的主要红外频率发生红移．相反,羟基的存在改善了分子的对称性,扩展了共轭体系,使能隙变窄,荧光光谱及电子光谱的主要吸收峰发生红移．同时由于羟基的供电效应,C-H伸缩振动发生蓝移．     

(BN)25团簇的结构与性能

采用密度泛函理论的杂化密度泛函（B3LYP）方法,在6-31G （d）基组水平上,对（BN）₂₅团簇进行结构优化和频率计算,得到基态构型,并对其稳定性、自然键轨道（NBO）、振动光谱和NICS进行计算.结果表明：（BN）₂₅团簇的能隙值较高,具有良好的化学稳定性;B原子和N原子的内部及原子之间都会发生s、p轨道杂化,原子之间有少量电荷转移;（BN）₂₅团簇的红外光谱和拉曼光谱都有较多振动峰;（BN）₂₅团簇具有芳香性.     

Energy bands of atomic monolayers of various materials: Possibility of energy gap engineering

The mobility of graphene is very high because the quantum Hall effects can be observed even at room temperature. Graphene has the potential of the material for novel devices because of this high mobility. But the energy gap of graphene is zero, so graphene cannot be applied to semiconductor devices such as transistors, LEDs, etc. In order to control the energy gaps, we propose atomic monolayers which consist of various materials besides carbon atoms.To examine the energy dispersions of atomic monolayers of various materials, we calculated the electronic states of these atomic monolayers using density functional theory with structural optimizations. The quantum chemical calculation software Gaussian 03 was used under periodic boundary conditions. The calculation method is LSDA/6-311G(d,p), B3LYP/6-31G(d), or B3LYP/6-311G(d,p).The calculated materials are C (graphene), Si (silicene), Ge, SiC, GeC, GeSi, BN, BP, BAs, AlP, AlAs, GaP, and GaAs. These atomic monolayers can exist in the flat honeycomb shapes. The energy gaps of these atomic monolayers take various values. Ge is a semimetal; AlP, AlAs, GaP, and GaAs are indirect semiconductors; and others are direct semiconductors.We also calculated the change of energy dispersions accompanied by the substitution of the atoms. Our results suggest that the substitution of impurity atoms for monolayer materials can control the energy gaps of the atomic monolayers.We conclude that atomic monolayers of various materials have the potential for novel devices.     

DFT study of the biphenylene–NO complexes formed in nitration mechanism

The most probable complexes formed in biphenylene (BP) nitration pathway have been investigated at B3LYP/6‐31+G(d,p) level of theory in the gas phase. To obtain more accurate energies, single point calculations were carried out at B3LYP/6‐31++G(2d,2p), B3PW91/6‐31+G(d,p), and B3PW91/6‐31++G(2d,2p) levels using B3LYP/6‐31+G(d,p) optimized geometry. The six intermediates and one transition state were found before the subsequent formation of the arenium ion on the potential energy surface of the electrophilic nitration of BP. It was also shown that the position β in the BP is much more susceptible to electrophilic attack than the competing position α. The Natural Bond Orbital (NBO), Charges from Electrostatic Potentials using a Grid based method (CHelpG), and Merz–Singh–Kollman (MK) charges and s‐characters of atoms involved in the reaction mechanism were calculated. Inspection of charges in the moieties indicates that the positive charge in all complexes is chiefly located on the BP, which means that theNO₂ moiety received the electron from the BP. To investigate the nature of BP– interaction in the five π‐complexes, atoms in molecules (AIM) analysis was performed. The AIM results suggested that the BP– interactions have an electrostatic characteristic. In addition, high electrostatic interactions were predicted in π‐complexes in which one of the oxygen atoms of interacts with the BP. Nucleus‐independent chemical shift (NICS) methodology has been applied to study the change of antiaromaticity in four‐membered ring of BP upon complexation with . The results based on NICS calculations show that antiaromaticity of four‐membered ring decreases upon complexation. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of hydrogen bond formation on the NMR properties of microhydrated ortho-aminobenzoic acid

The in?uence of the hydrogen bond formation on the nuclear magnetic resonance parameters has been investigated in the case of microhydrated ortho-aminobenzoic acid (o-Abz) in the gas-phase. DFT-B3LYP/aug-cc-pVDZ predicted ¹H and ¹³C isotropic chemical shifts with respect to TMS of the isolated o-Abz are in reasonable agreement with available experimental data. The isotropic and anisotropic chemical shifts for all atoms of o-Abz within the o-Abz?···?(H₂O)_1-3 complexes have been calculated at the Hartree–Fock, and density functional (B3LYP) theoretical levels using the 6-31++G(2d,2p) and aug-cc-pVDZ basis sets and considering the counterpoise corrections for the basis set superposition errors. The chemical shift values of the carboxyl group atoms of microhydrated o-Abz relative to isolated o-abz do not show significant basis set dependence. Both the hydrogen and carbon atoms constituting the carboxyl group of o-Abz suffer downfield shift due to formation of hydrogen bond with water. The length of hydrogen bond formed between o-Abz and water is found to vary with the number of water molecules present around o-Abz. A direct correlation between the hydrogen bond length and isotropic chemical shift of the bridging hydrogen is observed for both C?=?O?···?H-O and O-H?···?O interactions.     

Theoretical evaluation of NMR shifts in polycyclic aromatic hydrocarbons

ABSTRACT

Using computational chemistry methodology, we evaluate the proton magnetic shieldings and the corresponding chemical shifts of 12 polycyclic aromatic hydrocarbons that derive from chrysene, perylene and picene. Due to the large size of the studied compounds, we resort to density functional theory (DFT) and use it together with the B3LYP and the KT1 functionals. After a systematic method and basis set selection study carried out on methane, benzene and anthracene, the DFT(B3LYP) method and the 6-31G*, 6-31G** and 6-311++G** bases are selected to carry out the calculations, because of the efficiency in providing shifts close to the experimental data available. Additionally, we select the DFT(KT1) method together with the aug-pcS-1 basis set, and HF/6-31G* shifts are also calculated. In order to estimate the error in the theoretical results, we take as reference accurate experimental chemical shifts obtained for the molecules under investigation. Extra measurements are needed for this purpose and are included in the present work. The best combination of method and basis set is DFT(B3LYP)/6-31G**, proving to be very efficient in getting shifts close to experiment at a relatively low computational cost, and therefore we recommend it for the evaluation of proton shifts in larger polycyclic aromatic hydrocarbons.     

Effects of delocalised π-electrons around the linear acenes ring (n = 1 to 7): an electronic properties through DFT and quantum chemical descriptors

Π-electrons in chemical structure are the unique part of the fundamental particles that modify many interesting properties among the organic semiconductor molecules. By comparing the ground state energy, electronic properties and chemical indices within RHF/6-311G, B3LYP/6-311(G), B3LYP/6-311G(d,p), MP2/6-311G* and Cam-B3LYP/aug-cc-pvdz basis set at level of the theory, we identify that the resonance and the inductive effect of the delocalisation of electrons around the acene molecules could be responsible for acenes electronic and chemical properties. The total energies, energy gaps, HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energy gaps, electron affinity and ionisation potential are close to the experimental and theoretical results. Among the chemical indices, electrophilicity (ω), electronegativity (χ) and chemical hardness (η) observed to decrease as the acenes ring increasing, whereas the softness (S) and chemical potential (μ) increase with increasing the number of carbons around the acene molecules. The study is extended to electronics and chemical properties of the acene.     

A computational NICS and 13C NMR characterization of the substitution patterns of C70−2x(BN)x fullerenes (x=1–25)

A density functional study has been performed to investigate the electronic and magnetic properties of BN substituted fullerenes C_70?2x(BN)_x (x=1, 2, 3, 6, 9, 12, 15, 17, 19, 21, 23 and 25) based on the NMR parameters and NICS index. The calculated ¹³C chemical shielding (CS) tensors are found to be perturbed at the first and second neighbors of the doped atoms while the other distant carbon atoms not to be influenced significantly. ¹³C Chemical shifts (δ_iso) of the second neighbors of nitrogen and boron are significantly shifted to upfield and downfield (the second neighboring effects), respectively. Besides, chemical shifts are also affected by the curvature of the corresponding sites; for example, the perturbed sites at the caps yield smaller absolute values of chemical shifts than those located at the equator. Nucleus independent chemical shifts (NICS) at the cage centers of heterofullerenes (from ?25.29 to ?8.80) demonstrate that all the substituted species are aromatic, but less than C₇₀ (?27.29). The predicted NICS values may be useful for identification of the heterofullerenes through their endohedral ³He NMR chemical shifts.     

Theoretical Study of the Electronic and Optical Properties to Design Dye-Sensitivity for Using in Solar Cell Device

In this work, the structural and optoelectronic properties of phenanthrene-1,3,4-thaidiazoles oligomers were calculated using density functional theory (DFT) at B3LYP/6-31G(d) basis set level, to evaluate their possible application as organic semiconductor materials in photovoltaic and solar cell devices. For this reason, the energy gaps, frontier orbital (HOMO, and LUMO) distributions, total energies, Fermi level energies, work functions and maximum wavelength absorption, vertical absorption energies, and oscillator strengths have been investigated and discussed. The structures of phenanthrene-1,3,4-thiadiazoles oligomers are expanded from 1 to 10 thiadiazole monomeric units, to examine the increase of thiadiazole monomeric units on the optoelectronic properties. We observed that increased the number of monomeric units lead to significantly enhance the optoelectronic properties, which caused to decrease the gap energy from 3.69 eV in the structure with one thiadiazole ring just to 2.36 eV with 10 units. These changes give the shift of maximum absorption wavelengths from 376 to 578 nm. Consequently, these molecules have main absorption bands within the solar spectrum, to give the best performance for photovoltaic and organic solar cells devices.