B环对位取代异黄酮化合物的核磁共振研究

对14个合成的B环对位取代异黄酮化合物核磁共振氢谱进行了研究.利用超导核磁共振归属了B环无取代异黄酮质子的化学位移,根据取代基化学位移的变化影响规律考察了取代基对分子的影响方式.研究结果表明,2'(6'),3'(5')位质子共振迁移分别与取代基参数σ_p和S_o线性相关,说明4'位取代基主要通过电子效应影响其间位质子,其磁各向异性仅影响邻位质子,该取代基对A环质子影响不大,而对C环尤其是对2-H影响较明显.     

3种聚酰亚胺分子的核磁共振碳谱及氢谱的分析

本文报道了３种高性能聚酰亚胺的核磁共振定量碳谱及氢谱。利用这３种样品化学结构的相似性，根据ＰＥＩ和ＤＥＰＴ谱，ＰＥＩ和ＰＯＩ的二维同核化学位移相关谱，碳氢自旋晶格驰豫时间以及化学位移的理论计算，详细分析并归属了３种聚酰亚胺的碳谱峰和氢谱峰，同时验证了其重复单元结构的正确性。     

羟基蒽醌衍生物中羟基质子的核磁共振研究

通过对23个羟基蒽醌衍生物的质子核磁共振研究, 观察了不同取代类型羟基的化学位移范围;讨论了酚羟基乙酰化对芳环质子的化学位移影响, 为羟基取代位置的确定及芳环质子谱线归属提供了某种判据.此外, 还用HMO 法探讨了各类取代羟基的氢键强度及羰基迫位仅有一个羟基的内氢键强度与给予原子电荷密度的关系.本文报道一系列新型冠醚N,N'-双取代-1,7-二氧杂-12-冠-4(1~6), N,N' -双取代-1, 7-二氮杂-15冠-5(7~10) 及N,N'-双取代-1,10-二氮杂-18-冠-6(11~14)的质谱. 借助联动扫描和去焦技术对它们的开裂机理作了详细探讨.     

聚甲基丙烯酸乙酯链结构核磁共振(NMR)研究

本文用~1H-NMR,~(13)C-NMR和化学位移相关谱(COSY)研究了聚甲基丙烯酸乙酯(PEMA)的链结构.虽然质子峰的重叠给谱的识别带来一些困难,但是利用H-H COSY和C-H COSY提供的信息讨论了PEMA的~1H谱和~(13)C谱中各谱峰的归属.归属β-CH_2的四元组立构序列仍有一些问题.最后计算了无规PEMA的五元组立构序列分布.     

Mycoepoxydiene核磁共振谱的理论研究

用密度泛涵理论(Density Functional Theory,DFT)的B3PW 91方法在6-311G**基组下优化了标题化合物mycoepoxyd iene的几何构型,同时计算了红外光谱.并用规范不变原子轨道(gauge independent atom ic orb ital)G IAO/B3PW 91以及G IAO/HF方法分别在6-311G**,6-311++G**等基组进行了核磁共振谱研究,计算结果与实验结果吻合很好.     

含氟不饱和酯的~(13)C核磁共振谱

本文报道了含氟不饱和酯的~(13)C化学位移和偶合常数。并根据碳上电荷转移、杂化程度以及邻接基团的电荷密度,解释了炔碳的化学位移和氟碳偶合常数。     

镧系金属有机配合物的研究——ⅩⅠⅩ.二茂型氯化钇和镥的~1H和~(13)C核磁共振谱

核磁共振法已深入了金属有机化学领域的研究。其中,对于二茂夹心化合物,已用~1H和~(13)C 核磁共振方法研究了取代基影响环戊二烯基配位体的屏蔽效应。而用于研究稀土环     

酞侧基聚芳醚砜的核磁共振研究──PES－C的氢谱归属及碳谱峰的确认

用１３Ｃ－ＮＭＲ谱和二维异核化学位移相关谱（ＨＥＴＣＯＲ）归属了酞侧基聚芳醚砜（ＰＥＳ－Ｃ）的１Ｈ－ＮＭＲ谱峰，并经二维同核化学位移相关谱（ＣＯＳＹ）验证．对原１３Ｃ－ＮＭＲ谱峰归属作了部分修正．二维同核及异核相关谱为ＰＥＳ－Ｃ的碳、氢核磁谱峰归属提供了重要信息．由ＰＥＳ－Ｃ的核磁谱图可见其链结构的规整性     

三取代环丙烷的^1^3C核磁共振谱研究

前文曾报道三取代环丙烷的质子核磁共振谱及其解析结果,讨论了取代基对化学位移和偶合常数的影响.环丙烷的~(13)C核磁共振谱研究报道极少。Monti等人研究了甲基、溴代和乙炔基环丙烷的~(13)C核磁共振谱,发现在多取代的环丙烷中,取代基相互之间的影响是很显著的.Clague等人亦报道了一系列环丙烷的~(13)C核磁共振谱,但未有详细的分析.本文报道10种尚未见载于文献的三取代环丙烷的~(13)C核磁共振谱,数据见表1. 在1,2,3-三取代环丙烷中,由于取代基的相互作用,影响环上碳的化学位移的因素是比较复杂的.从我们测定化合物的数据来看,取代基为CH_3的环上碳的平均化学位移为29.24     

膦类化合物核磁共振谱化学位移预测

采用离子性指数(INI)、立体效应参数(iε)对291个膦化合物中磷原子进行结构表征,并与其核磁共振磷谱(31P NMR)建立定量结构波谱关系(QSSR)模型。分别利用多元线性回归(MLR)、偏最小二乘回归(PLSR)、人工神经网络(ANN)建模,同时采用内部及外部双重验证的办法对所得模型稳定性能进行深入分析和检验,建模计算值、留一法(LOO)交互校验(CV)预测值和外部样本预测值的复相关系数Rcum、QLOO和Qext分别为0.9449,0.9408和0.9338(MLR);0.9421、0.9411和0.9338(PLSR);0.9741、0.9736和0.9471(ANN)。结果表明:INI、iε与31P NMR谱化学位移显著相关。     

AM1 study of photoelectron spectra

A correlation was found between the group dipole moments of substituents determined from the dipole moments of ethylene derivatives and the second ionization potentials of allene derivatives corresponding to the -MO of the C()-C() bond. It was shown that the concept of the effect of the substituent field cannot completely explain the observed phenomena, and the energies of the second ionic states of bromoallene and alkoxyallenes are lowered because of the interaction between nonbonded fragments through the systems of the compounds. It has been found that, in terms of orbital approximation, this interaction causes electronic destabilization of theanti-planar (trans) conformers of methoxyallene and methyl vinyl ether compared to theirsin-planar (cis) forms.For Part 5, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 48–54, January, 1995.     

量子化学计算在有机化合物核磁共振教学中的应用

用量子化学方法计算化合物的核磁共振数据并与实验数据进行比较已经广泛应用于复杂天然产物构型的确定。以核磁共振教学为例,介绍量子化学计算在有机化合物波谱解析教学中的具体应用。通过计算核磁共振氢谱和碳谱的化学位移值,辅助解析分子结构,帮助学生对电子的分布、原子核的化学环境等有更直观的认识,有利于学生理解核磁共振的本质,有效提高学生的学习兴趣和积极性。同时,让学生了解量子化学计算在核磁共振中的应用,了解化学研究的前沿手段,开阔学生视野,培养学生解决实际问题的能力。     

Intermolecular interactions in uracil–nitrous acid complexes: structures,binding energy,topological properties,and nuclear magnetic resonance study

Molecular interactions between uracil and nitrous acid (U–NA) [C₄N₂O₂H₄? NO₂H] have been studied using B3LYP, B3PW91, and MP2 methods with different basis sets. The optimized geometries, harmonic vibrational frequencies, charge transfer, topological properties of electron density, nucleus‐independent chemical shift (NICS), and nuclear magnetic resonance one‐ and two‐bonds spin–spin coupling constants were calculated for U–NA complexes. In interaction between U and NA, eight cyclic complexes were obtained with two intermolecular hydrogen bonds N(C)HU…N(O) and OH_NA…O_U. In these complexes, uracil (U) simultaneously acts as proton acceptor and proton donor. The most stable complexes labeled, UNA1 and UNA2, are formed via NH bond of U with highest acidity and CO group of U with lowest proton affinity. There is a relationship between hydrogen bond distances and the corresponding frequency shifts. The solvent effect on complexes stability was examined using B3LYP method with the aug‐cc‐pVDZ basis set by applying the polarizable continuum model (PCM). The binding energies in the gas phase have also been compared with solvation energies computed using the PCM. Natural bond orbital analysis shows that in all complexes, the charge transfer takes place from U to NA. The results predict that the Lone Pair (LP)(O)_U → σ*(O? H) and LP(N(O)_NA → σ*(N(C)? H)_U donor–acceptor interactions are most important interactions in these complexes. Atom in molecule analysis confirms that hydrogen bond contacts are electrostatic in nature and covalent nature of proton donor groups decreases upon complexation. The relationship between spin–spin coupling constant (^1hJ_H…_Y and ^2hJ_H…_Y) with interaction energy and electronic density at corresponding hydrogen bond critical points and H‐bonds distances are investigated. NICS used for indicating of aromaticity of U ring upon complexation. © 2013 Wiley Periodicals, Inc.     

Absorption spectra of poly-N-vinylcarbazole derivatives by experiment and simulation

Geometry molecular optimization and quantum chemical simulations of absorption spectra for newly synthesized poly-N-vinylcarbazole derivatives were performed using a semi-empirical approach. The studied polymers were modified by changing the positions of the carbazole group with respect to the polymer backbone. The absorption spectra were calculated for different numbers of PNVK monomers. A sufficient agreement between the calculated and experimentally measured spectra was observed. A change of the red shift absorption with respect to the blue shift was observed for cases when the number of monomers was higher than 4. The theoretical simulations indicate that this behavior is a consequence of the specific molecular structure of the considered molecules. The results demonstrate the potential of combined simulation and experimental studies in materials engineering and searching of new electro-luminescent materials.     

8-甲硫基喹啉及其两种衍生物UV-Vis光谱的理论研究

The ground state structures of 8-methylthioquinoline and its two absorption spectra were calculated using TD-DFT method.Calculation results agree with experimental values.Calculation results indicate that the position of lowest-energy absorption bands will be red-shifted and blue-shifted,when one hydrogen atom of methyl group is substituted by -Si(CH3)3 and -Si(OCH3)3 groups,respectively.And the energies of HOMO and LUMO of substitutents increase to a different extent,and the position of lowest-energy absorption bands and the energy gap vary slightly.     

Spectroscopic Studies of 1-Aryl-2,2-Dichlorocyclopropanes

Seventeen 1-aryl-2,2-dichlorocyclopropanes were examined by using IR, ¹³C NMR, and mass spectrometry. The data obtained from IR and ¹³C NMR spectra indicate that the bond strength of carbon-chlorine on the cyclopropane ring and the electron density of that carbon depend on the substituent. The mass fragmentation patterns of compounds in this series resemble those of the dibromo analogues. The fragmentation mechanism is proposed to involve the formation of indenium ion through an electrocyclization.     

Pyrolysis and mass spectra of trimethylsilyl derivatives of monosaccharides

The pyrolysis of trimethylsilyl derivatives of saccharides (1) was investigated by DTA-TG, MS, GC/MS and TG-GC/MS. The DTA-TG/DTG curves showed that the pyrolysis of 1 occurred in one stage. The exothermic peaks were due to sublimation or thermal decomposition by vaporization. The cleavage mechanism by electron impact of 1 was classified into four categories: 1) stepwise elimination of the side-chain, 2) cleavage of the side-chain, 3) cleavage of the pyranose ring, and 4) cleavage of the pyranose ring and side-chain at the same time. The mass-spectrum for 1 revealed the main common four fragment ions, such asm/z 73, 191, 204 and 217, with cleavage of the pyranose ring. These fragment ions were detected with a similar retention time in the gas cromatogram by GC/MS or TG-GC/MS. The retention time for 1 increased in the sequence aldopentose相似文献   

An alternative interpretation of the chemical shift of the water proton in aqueous tetraalkylammonium halide solutions at various temperatures

An alternative explanation of the behavior of proton magnetic resonance chemical shifts of the water proton in aqueous tetraalkylammonium salt solutions is presented. It involves independent ion-solvent interactions and rapid exchange on the NMR time scale with the bulk water. Our explanation fits the known data and clearly shows why the observed chemical shift is linear with molality at low concentrations.     

Lithiation–alkylation of polystyrene occurs only on the ring

When polystyrene is treated with an organolithium reagent, the hydrogen on the para carbon is removed and this position may be alkylated with e.g., iodomethane or chlorotrimethylsilane. The metalation occurs directly at this position and does not involve metalation at the benzylic carbon with resonance distribution of the charge to the ring. The reaction of cumene with butyllithium also occurs by direct ring metalation and it is shown that these results are consistent with both the kinetic and the thermodynamic acidity of the hydrocarbons. © 1997 John Wiley & Sons, Inc.     

Systematic investigation on the geometric dependence of the calculated nuclear magnetic shielding constants

We perform a systematic examination on the dependence of the calculated nuclear magnetic shielding constants on the chosen geometry for a selective set of density functional methods of B3LYP, PBE0, and OPBE. We find that the OPBE exchange-correlation functional performs remarkably well when either the optimized geometries or the experimental geometries are used. The popular B3LYP and PBE0 functionals have a clear tendency of deshielding, giving shieldings that are usually too low and shifts that are usually too high, at the experimental geometries. Combined with the Hartree-Fock geometries, however, much improved magnetic constants are obtained for B3LYP and PBE0, due to the compensation effect from the systematic underestimation of bond lengths by the Hartree-Fock method.