新喜树碱衍生物的核磁共振谱分析与结构鉴定

以20(S)-喜树碱(CPT)为起始原料,对其进行结构修饰,合成了一种新的喜树碱衍生物CPT-A.并利用1D(~1H、~(13)C和DEPT135)和2D(异核单量子相关谱和异核多碳相关谱)核磁共振(NMR)技术对该化合物进行了结构确定,详细归属了CPT-A~1H和~(13)C NMR谱的化学位移,喜树碱骨架的指认结果与文献报道基本一致,并发现喜树碱骨架6位碳与取代基苯环3’位碳的化学位移相同,谱峰完全重叠,这在~(13)C谱中是不常见的.研究结果可为喜树碱类天然产物的发现和结构鉴定提供NMR数据支持和方法指引.     

毛冬青三萜皂甙Ilexsaponin B3糖部分的核磁共振法分析

采用1H、13C、DEPT(无畸变极化转移增益法)、1H-1H COSY(氢-氢化学位移相关谱)、1H-1HTCOSY(氢-氢化学位移全相关潜)、HSQC(异核单量子相关谱)、HMBC(异核多键相关谱)等多种NMR分析方法,首次对毛冬青三萜皂甙Ilexsaponin B3的1H和13C NMR信号进行了全归属,特别是应用1H-1H COSY和1H-1H TCOSY相结合的分析方法,对该化合物中氢谱信号严重重叠的糖部分进行了详细的分析,提出了一套对三萜皂甙糖部分信号进行全归属的核磁共振法.     

一种新的六氢嘧啶并嘧啶二酮衍生物的核磁共振分析

采用氢谱(1H NMR)、碳谱(13C NMR)、梯度场氢氢化学位移相关谱(1H-1H COSY)、梯度场质子检测异核单量子化学位移相关谱(HSQC)、梯度场质子检测异核多重键化学位移相关谱(HMBC)等多种NMR分析方法,确证了8a-对甲氧苯基-4,5-双(对氯苯基)六氢嘧啶[4,5-d]并嘧啶-2,7(1H,3H)-二酮的结构,对它的1H和13C NMR谱信号进行了归属,为其结构鉴定提供了重要依据。     

苯并咪唑萘酰亚胺类化合物的合成与结构确证

本文合成并分离提纯了1位和4位单取代的苯并咪唑萘酰亚胺(NBI)类化合物1~4,对化合物1的紫外-可见光谱、红外光谱、质谱、核磁共振谱(包括1H NMR、13C NMR、DEPT、1H-13C HSQC、1H-13C HMBC、1H-1HCOSY多种NMR技术)进行了详细解析,对其所有的1H和13C NMR信号进行了归属,并使用了GIAO和CSGT两种方法量化计算核磁位移,通过多种波谱学技术确证了化合物的结构。     

2-苯基苯并噻唑的~(13)C NMR取代基效应研究

本文通过测定和解析14个2-苯基苯并噻唑化合物的~(13)C NMR谱,研究了芳杂环上的取代基效应和不同取代基对分子内核电荷密度分布的影响,分析了影响~nJ~(13)C-~1H的结构因素。应用对照分析法研究了苯并噻唑取代基对苯环的微扰作用,得到了苯并噻唑取代基的诱导化学位移值,并作了芳环~(13)C化学位移的经验计算,计算值和实验值相符。用EHMO方法(广义Hückel分子轨道法)对化合物2,3,9作了理论计算,将计算所得的碳原子的总电荷密度与~(13)C化学位移作了回归分析,相关因子为0.96。     

光谱法分析乙丙共聚物的序列结构及链节比

用FTIR, 1 H NMR和 13 C NMR分析乙丙共聚物的序列结构与链节比. 通过对乙丙共聚物 1 H NMR, 13 C NMR和 13 C-1 H二维核磁共振谱的综合分析, 提出了与前人不同的归属, 并提出了不同位置碳原子积分面积相关性分析方法, 该方法避免了烦琐的理论计算, 可简便地得到乙丙共聚物的主要序列结构. 通过比较 1 H NMR和 13 C NMR计算乙丙共聚物中乙烯、 丙烯链节比, 表明可以用 1 H NMR代替 13 C NMR完成对乙丙共聚物中乙烯、 丙烯链节比的定量计算.     

新药普卢利沙的核磁共振研究

应用同核化学位移相关谱(1H-1H COSY)、氢检出异核多量子相关谱(HMQC)、氢检出多键异核多量子相关谱(HMBC)等二维谱核磁共振技术,参考19F-1H和19F-13C的偶合裂分情况对抗菌新药普卢利沙的1H NMR、13C NMR谱的信号进行了全归属。     

1,3-双(偶氮介晶基)-1,1,3,3-四甲基二硅氧烷的 合成、2D NMR结构分析和液晶性能

合成了2个(CH3(C6H4)N2(C6H3A)COO(C6H4)OCH2-Si(CH3)2)2O化合物,其中A = H为1,A = CH3为2。经IR、1H NMR和元素分析表征,并用2D NMR1H-1H COSY记录了2个化合物中不同取代基苯环上所有质子的化学位移和相关-自旋偶合常数,对谱线的归属作了指认。通过偏光显微镜和DSC分析,1具有液晶性能,而2没有液晶性能。同时,用AM1方法计算了它们的电子结构,讨论了它们的结构与性能之间的关系。     

二萜生物碱的~(13)C核磁共振谱

本文通过对186个二萜生物碱及其衍生物的~(13)C NMR谱数据的分析比较,就以下几方面作了归纳总结:①信号归属的方法;②常见取代基OCH_3、NCH_3、、NCH_2CH_3、OCOCH_3、的化学位移范围;③季碳和某些特定碳的化学位移规律。某些特定结构,如C_(20)二萜生物碱中的噁唑烷环以及C_(20)差向异构体等的~(13)C NMR谱特征;④C_(19)二萜生物碱中不同位置上取代基(H→OH、H→OMe、OH→OAc、OH→OMe、OH→C=O)效应和立体化学效应。这些归纳总结有助于此类化合物结构的阐明。     

线性标度方法计算几个藜芦生物碱的13C NMR化学位移

本文采用几种密度泛函方法计算了环杷明(cyclopamine)的~(13)C NMR化学位移。与实验值比较发现采用B97-2/pcSseg-1的气相优化结构结合SMD溶剂化模型计算获得的~(13)C NMR化学位移最合适。在此基础上,对藜芦中的五种典型生物碱结构(环杷明、介芬胺、藜芦胺、计明胺和棋盘花胺)进行了相应的~(13)C NMR化学位移计算。通过与实验值进行拟合,得到线性标度公式σ=(184.4-σ_(cal))/1.0261。其相关系数R~2=0.9976。此外,理论计算也可以解决化合物中的相似碳的~(13)C NMR化学位移归属困难的问题。线性标度方法获得化学位移对建立天然产物的NMR数据库、匹配结构和解析实验测试数据提供了一种快捷可靠的解决方案。     

Molecular structure, IR and NMR spectra of 2,6 distyrylpyridine by density functional theory and ab initio Hartree-Fock calculations

Vibrational frequencies and gauge including atomic orbital (GIAO) 13C NMR and 1H NMR chemical shift values of 2,6 distyrylpyridine (C21H17N) in the ground state have been calculated by using the Hartree-Fock (HF) and density functional method (B3LYP) with 6-31G(d) basis set. These methods are proposed as a tool to be applied in the structural characterization of 2,6 distyrylpyridine (C21H17N). The title compound has C2v point group, thus providing useful support in the interpretation of experimental IR data. In addition, obtained results were related to the linear correlation plot of experimental 13C NMR, 1H NMR chemical shifts values and IR data.     

How reliable are GIAO calculations of 1H and 13C NMR chemical shifts? A statistical analysis and empirical corrections at DFT (PBE/3z) level

Reliability of calculated (1)H and (13)C NMR chemical shifts for various classes of organic compounds obtained with gauge-invariant atomic orbital (GIAO) approach has been studied at the PBE/3ζ level (as implemented in PRIRODA code) using linear regression analysis with experimental data. Empirical corrections for the calculated chemical shifts δ(H,calc) = δ(PBE/3ζ) - 0.08 ppm (RMS 0.18 ppm, MAD 0.66 ppm) and δ(C,calc) = δ(PBE/) (3) (ζ) - 6.35 ppm (RMS 3.09 ppm, MAD 9.42 ppm) have been developed using the sets of 263 and 308 experimental values for (1)H and (13)C chemical shifts, respectively. The confidence intervals of NMR chemical shifts at 95% confidence probability are δ(H,calc) ± 0.35 ppm for (1)H and δC,calc) ± 6.05 ppm for (13)C.     

Experimental and theoretical NMR study of 4-(3-cyclohexen-1-yl)pyridine

(1)H, (13)C, DEPT, COSY, NOESY and HETCOR NMR spectra of 4-(3-cyclohexen-1-yl)pyridine (4-Chpy) have been reported for the first time. (1)H and (13)C NMR chemical shifts of 4-Chpy (C(11)H(13)N) have been calculated by means of the Hartree-Fock (HF) and Becke-3-Lee-Yang-Parr (B3LYP) density functional methods with 6-311++G(d,p) basis set. Comparison between the experimental and the theoretical results indicate that density functional B3LYP method is superior to the scaled HF approach for predicting NMR properties.     

FT-IR and NMR investigation of 1-phenylpiperazine: a combined experimental and theoretical study

FT-IR and (1)H, (13)C, DEPT, COSY, NOESY, HETCOR, INADEQUATE NMR spectra of 1-phenylpiperazine (pp) have been reported for the first time except for its (1)H NMR spectrum. The vibrational frequencies and (1)H, (13)C NMR chemical shifts of pp (C(10)H(14)N(2)) have been calculated by means of the Hartree-Fock (HF) and Becke-Lee-Yang-Parr (BLYP) or Becke-3-Lee-Yang-Parr (B3LYP) density functional methods with 6-31G(d) and 6-31G(d,p) basis sets, respectively. Comparison between the experimental and the theoretical results indicates that density functional B3LYP method is superior to the scaled HF and BLYP approach for predicting vibrational frequencies and NMR properties.     

Structure-NMR chemical shift relationships for novel functionalized derivatives of quinoxalines

(1)H, (13)C and (15)N NMR chemical shifts for a variety of novel quinoxalines were determined by different 2D methods and were calculated using the GIAO DFT approach. Comparison with experimental data shows good correlations in the case of (1)H, (13)C and (15)N chemical shifts. Different combinations of basis sets were tested. In non-polar solvents quinoxalines exist as dimers owing to strong hydrogen bonding. Calculations for dimers improve the correlation between experiment and theory. Additive empirical methods for estimating chemical shifts have drawbacks and have to be used with a great care for this type of compound.     

Experimental (FT-IR, FT-Raman, H, C NMR) and theoretical study of alkali metal 2-aminonicotinates

The influence of lithium, sodium, potassium, rubidium and cesium on the electronic system of 2-aminonicotinic acid (2-ANA) was studied by the methods of molecular spectroscopy. The vibrational (FT-IR, FT-Raman) and NMR (¹H and ¹³C) spectra of 2-aminonicotinic acid and its alkali metal salts were recorded. Characteristic shifts and changes in intensities of bands along the metal series were observed. The changes of chemical shifts of protons (¹H NMR) and carbons (¹³C NMR) in the series of studied alkali metal 2-aminonicotinates (2-AN) were observed too.Optimized geometrical structures of the studied compounds were calculated by the B3LYP method using the 6-311++G** basis set. Aromaticity indices, atomic charges, dipole moments and energies were also calculated. The theoretical chemical shifts in ¹H and ¹³C NMR spectra and theoretical wavenumbers and intensities of IR and Raman spectra were determined. The calculated parameters were compared to the experimental characteristics of the studied compounds.     

FT-IR and NMR investigation of 2-(1-cyclohexenyl)ethylamine: a combined experimental and theoretical study

FT-IR and (1)H, (13)C, DEPT, HETCOR, COSY, and NOESY NMR spectra of 2-(1-cyclohexenyl)ethylamine (CyHEA) have been reported for the first time. The vibrational frequencies and (1)H, (13)C NMR chemical shifts of CyHEA (C(8)H(15)N) have been calculated by means of the Hartree-Fock (HF), Becke-Lee-Yang-Parr (BLYP) and Becke-3-Lee-Yang-Parr (B3LYP) density functional methods with 6-31 G(d) and 6-31 G(d,p) basis sets, respectively. The comparison between the experimental and the theoretical results indicates that density functional B3LYP method is superior to the scaled HF and BLYP approach for vibrational frequencies and predicting NMR properties.     

Synthesis and Chemical Shifts Calculation of a-Acyloxycarboxamides Derived from Indane-l,2,3-trione by DFT and HF Methods

α-Acyloxycarboxamides are synthesized from three-component Passerini reaction between indane-1,2,3-trione, isocyanides, and thiophenecarboxylic acids in quantitative yields. The structures of the final products were confirmed by IR, 1H and 13C NMR spectroscopy, mass spectrometry, and elemental analysis. The B3LYP/HF calculations for computation of 1H and 13C NMR chemical shifts have been carried out for the title compounds at the 6-311+G** and 6-311++G** basis set levels within GIAO and CSGT approaches. Predicted 1H and 13C NMR che-mical shifts have been assigned and compared with experimental 1H and 13C NMR spectra and they are supported each other.     

Computational studies of 13C NMR chemical shifts of saccharides

The (13)C NMR chemical shifts for alpha-D-lyxofuranose, alpha-D-lyxopyranose (1)C(4), alpha-D-lyxopyranose (4)C(1), alpha-D-glucopyranose (4)C(1), and alpha-D-glucofuranose have been studied at ab initio and density-functional theory levels using TZVP quality basis set. The methods were tested by calculating the nuclear magnetic shieldings for tetramethylsilane (TMS) at different levels of theory using large basis sets. Test calculations on the monosaccharides showed B3LYP(TZVP) and BP86(TZVP) to be cost-efficient levels of theory for calculation of NMR chemical shifts of carbohydrates. The accuracy of the molecular structures and chemical shifts calculated at the B3LYP(TZVP) level is comparable to those obtained at the MP2(TZVP) level. Solvent effects were considered by surrounding the saccharides by water molecules and also by employing a continuum solvent model. None of the applied methods to consider solvent effects was successful. The B3LYP(TZVP) and MP2(TZVP)(13)C NMR chemical shift calculations yielded without solvent and rovibrational corrections an average deviation of 5.4 ppm and 5.0 ppm between calculated and measured shifts. A closer agreement between calculated and measured chemical shifts can be obtained by using a reference compound that is structurally reminiscent of saccharides such as neat methanol. An accurate shielding reference for carbohydrates can be constructed by adding an empirical constant shift to the calculated chemical shifts, deduced from comparisons of B3LYP(TZVP) or BP86(TZVP) and measured chemical shifts of monosaccharides. The systematic deviation of about 3 ppm for O(1)H chemical shifts can be designed to hydrogen bonding, whereas solvent effects on the (1)H NMR chemical shifts of C(1)H were found to be small. At the B3LYP(TZVP) level, the barrier for the torsional motion of the hydroxyl group at C(6) in alpha-D-glucofuranose was calculated to 7.5 kcal mol(-1). The torsional displacement was found to introduce large changes of up to 10 ppm to the (13)C NMR chemical shifts yielding uncertainties of about +/-2 ppm in the chemical shifts.