DFT and experimental determination of conformations of 2‐(ethoxycarbonylmethoxy)‐5‐(arylazo)benzaldehydes and their oximes

2‐(Ethoxycarbonylmethoxy)‐5‐(arylazo)benzaldehydes 1–4 and their oximes 5–8 were synthesized and characterized by IR, ¹H and ¹³C NMR spectroscopy. The favoured conformations of aldehydes 1–4 and oximes 5–8 were predicted theoretically. Selected geometrical parameters and charges were derived from optimized structures. IR, ¹H and ¹³C NMR data were also computed using Gaussian‐03 package and compared with the observed values. ¹⁵N and ¹⁷O chemical shifts were also determined theoretically. Copyright © 2012 John Wiley & Sons, Ltd.     

NMR spectral assignment of 2α- and 3β-methylhopanes and evidence for boat conformation in D ring of 17α(H),21α(H)-hopanes

The full (1)H and (13)C NMR chemical shift assignment of 2α-methyl-17α(H),21β(H)-hopane is presented. This compound is formed in mature sediments from biogenic sources of 2β-methyl-17β(H),21β(H)-hopanoids, which include several cyanobacteria. In addition, full (1)H and (13)C NMR chemical shift data of all four 17,21 isomers of 3β-methylhopane have been assigned. The thermodynamically most stable 3β-configuration corresponds to that found in bacterial sources. The data presented here suggest minor corrections to the (13)C chemical assignments reported earlier for 17α(H)-hopanes. Moreover, spectral evidence indicates an unexpected ring-D boat conformation of 17α(H),21α(H)-hopanes, which may serve to explain the steric strain reported for this isomer.     

A GIAO/DFT study of 1H, 13C and 15N shieldings in amines and its relevance in conformational analysis

The 1H, 13C and 15N absolute shieldings of 13 amines were calculated at the GIAO/B3LYP/6-311++G** level. For some compounds (ethylamine, piperidine and 1-methylpiperidine) two conformations were calculated. The 13C and 15N data could be correctly correlated with experimental chemical shifts, allowing the conformation of 1-methylpiperidine to be established. The 1H NMR absolute shieldings, although less well correlated with delta values, were used to account for the anisotropy effects of the N lone pair.     

Investigation of structure, vibrational and NMR spectra of oxycodone and naltrexone: a combined experimental and theoretical study

In this work, two important opioid antagonists, naltrexone and oxycodone, were prepared from thebaine and were characterized by IR, (1)H NMR and (13)C NMR spectroscopy. Moreover, computational NMR and IR parameters were obtained using density functional theory (DFT) at B3LYP/6-311++G** level of theory. Complete NMR and vibrational assignment were carried out using the observed and calculated spectra. The IR frequencies and NMR chemical shifts, determined experimentally, were compared with those obtained theoretically from DFT calculations, showed good agreements. The RMS errors observed between experimental and calculated data for the IR absorptions are 85 and 105 cm(-1), for the (1)H NMR peaks are 0.87 and 0.17 ppm and for those of (13)C NMR are 5.6 and 5.3 ppm, respectively for naltrexone and oxycodone.     

Experimental and GIAO 15N NMR study of substituent effects in 1H-tetrazoles

A series of 1-aryl/alkyl-1H-1,2,3,4-tetrazoles, 5-substituted 1H-tetrazoles, and 1,5- and 2,5-disubstituted 1H-tetrazoles were studied by a combination of experimental NMR (natural abundance (15)N, (15)N/(1)H HMBC, and (13)C) and computational GIAO-NMR techniques to explore substituent effects on (15)N (and (13)C) NMR chemical shifts in the tetrazole (TA) moiety. Computed (15)N chemical shifts via GIAO-B3LYP/6-311+G(2d,p) calculations gave satisfactory results in comparison with experimental data. Whereas N-alkylation leads to large (15)N chemical shift changes, changes in the N(1)-aryl derivatives bearing diverse substituent(s) are generally small except for polar ortho-substituents (COOH, NO(2)). Large Δδ(15)N values were computed in N(1)-aryl derivatives for p-COH(2)(+) and p-OMeH(+) as extreme examples of electron-withdrawing substituents on a TA moiety.     

Density functional theory investigation of hydrogen bonding effects on the oxygen, nitrogen and hydrogen electric field gradient and chemical shielding tensors of anhydrous chitosan crystalline structure

A systematic computational investigation was carried out to characterize the 17O, 14N and 2H electric field gradient, EFG, as well as 17O, 15N, 13C and 1H chemical shielding tensors in the anhydrous chitosan crystalline structure. To include the hydrogen-bonding effects in the calculations, the most probable interacting molecules with the target molecule in the crystalline phase were considered through a hexameric cluster. The computations were performed with the B3LYP method and 6-311++G(d,p) and 6-31++G(d,p) standard basis sets using the Gaussian 98 suite of programs. Calculated EFG and chemical shielding tensors were used to evaluate the 17O, 14N and 2H nuclear quadrupole resonance, NQR, and 17O, 15N, 13C and 1H nuclear magnetic resonance, NMR, parameters in the hexameric cluster, which are in good agreement with the available experimental data. The difference between the calculated NQR and NMR parameters of the monomer and hexamer cluster shows how much hydrogen bonding interactions affect the EFG and chemical shielding tensors of each nucleus. These results indicate that both O(3)-H(33)...O(5-3) and N-H(22)...O(6-4) hydrogen bonding have a major influence on NQR and NMR parameters. Also, the quantum chemical calculations indicate that the intra- and intermolecular hydrogen bonding interactions play an essential role in determining the relative orientation of EFG and chemical shielding principal components in the molecular frame axes.     

(s)-多沙唑嗪的核磁共振理论和实验研究

报道了(s)-多沙唑嗪的1H、13C、DEPT、1H-1H COSY等的NMR波谱数据, 并对1H、13C NMR信号进行了指认. (s)-多沙唑嗪分子中含有9个季碳原子, 其中绝大部分通过常规实验的方法难以指认. 应用量子化学规范不变原子轨道(GIAO)的Becke-3-Lee-Yang-Parr(B3LYP)和Hartree-Fock(HF)方法, 分别在6-21G基组下计算了标题化合物的13C NMR化学位移值. 计算结果表明, 理论计算数据与实验结果吻合较好, 可以帮助对(s)-多沙唑嗪季碳原子NMR位移信号进行指认.     

Combined first-principles computational and experimental multinuclear solid-state NMR investigation of amino acids

13C, 14N, 15N, 17O, and 35Cl NMR parameters, including chemical shift tensors and quadrupolar tensors for 14N, 17O, and 35Cl, are calculated for the crystalline forms of various amino acids under periodic boundary conditions and complemented by experiment where necessary. The 13C shift tensors and 14N electric field gradient (EFG) tensors are in excellent agreement with experiment. Similarly, static 17O NMR spectra could be precisely simulated using the calculation of the full chemical shift (CS) tensors and their relative orientation with the EFG tensors. This study allows correlations to be found between hydrogen bonding in the crystal structures and the 17O NMR shielding parameters and the 35Cl quadrupolar parameters, respectively. Calculations using the two experimental structures for L-alanine have shown that, while the calculated isotropic chemical shift values of 13C and 15N are relatively insensitive to small differences in the experimental structure, the 17O shift is markedly affected.     

X-ray crystallographic and Mössbauer spectroscopic applications in dependence of partial quadrupole splitting, [R], on the C-Sn-C angle in seven-coordinated diorganotin(IV) complexes

The synthesis and the IR, NMR (1H, 13C, and 119Sn), and M?ssbauer spectroscopies and single-crystal X-ray diffraction studies of seven-coordinated diorganotin(IV) complexes, namely, [Ph2Sn(Hdapsc)]Cl.H2O.DMF [7; H(2)dapsc = 2,6-diacetylpyridine bis(semicarbazone)], [Me(2)Sn(H2,6Achexim)]Br.H2O [8; H(2)2,6Achexim = 2,6-diacetylpyridine bis(3-hexamethyleneiminylthiosemicarbazone)], [Me(2)Sn(dapmts)] [9; H(2)dapmts = 2,6-diacetylpyridine bis(4-methythiosemicarbazone)], and [nBu2Sn(dapmdtc)] [10; H(2)dapmdtc = 2,6-diacetylpyridine bis(S-methydithiocarbazate)], were done. The determination of the structures of [Ph(2)Sn(Hdapsc)]+, [Me2Sn(H2,6Achexim)]+ and [Me2Sn(dapmts)], [nBu2Sn(dapmdtc)] revealed the presence of monocationic and neutral complexes, respectively. The structures consist of monomeric units in which the Sn(IV) ions exhibit distorted pentagonal-bipyramidal geometries, with the X,N,N,N,X-donor (X = O, S) systems of the ligands lying in the equatorial plane and the organic groups in the apical positions. The C-Sn-C angle in the seven-coordinated diorganotin(IV) complexes was estimated using a correlation between M?ssbauer and X-ray data based on the point-charge model and using new values obtained in this work for [alkyl] = -1.00 mm s(-1) and [aryl] = -0.80 mm s(-1) for complexes containing O,N,N,N,O-pentadentate ligands and new values for [alkyl] = -0.87 mm s(-1) and [aryl] = -0.75 mm s(-1) for complexes containing S,N,N,N,S-pentadentate ligands.     

1H and 13C NMR chemical shift assignments of spiro-cycloalkylidenehomo- and methanofullerenes by the DFT-GIAO method

The (1)H and (13)C NMR chemical shifts of spiro-cycloalkylidene[60]fullerenes were assigned using experimental NMR data and the Density Functional Theory (DFT)-Gauge Independence Of Atomic Orbitals method (GAIO) calculation method in the Perdew Burke Ernzerhof (PBE)/3z approach. The calculated values of the (13)C NMR chemical shifts adequately reproduce the experimental values at this quantum chemistry approach. Similar assignments will be helpful for (13)C NMR spectral analysis of homo- and methano[60]fullerene derivatives for structure elucidation and to determine the influence of fullerene frames on substituents and the influence of substituents on fullerene cores.     

Reaction of m-terphenyldichlorophosphanes with sodium azide: synthesis and characterization of stable azidocyclophosphazenes

Reaction of the m-terphenyldichlorophosphanes 2,6-(2-MeC(6)H(4))(2)C(6)H(3)PCl(2) (1), 2,6-(4-t-BuC(6)H(4))(2)C(6)H(3)PCl(2) (2), or 2,6-Mes(2)C(6)H(3)PCl(2) (3) with excess NaN(3) in acetonitrile at room temperature afforded the corresponding bisazidophosphanes 2,6-(2-MeC(6)H(4))(2)C(6)H(3)P(N(3))(2), 2,6-(4-t-BuC(6)H(4))(2)C(6)H(3)P(N(3))(2) (5), or 2,6-Mes(2)C(6)H(3)P(N(3))(2) (6) (Mes = 2,4,6-Me(3)C(6)H(2)), respectively. These compounds are thermally labile and decompose into a number of azidophosphazenes. The azidocyclophosphazenes [NP(N(3))(C(6)H(3)(4-t-BuC(6)H(4))(2)-2,6)](3) (4) and [NP(N(3))C(6)H(3)Mes(2)-2,6](2) (8) have been isolated from these mixtures. All compounds were characterized by (1)H, (13)C, (31)P NMR and IR spectroscopy. Crystal structures of 2, 4, and 8 were determined.     

Experimental and theoretical study on IR and NMR spectra of several tetrachlorinated diphenyl sulfides

Tetrachlorinated diphenyl sulfides (TCDPSs) are environmentally interesting compounds. In this paper, both experimental and theoretical studies on IR and (1)H NMR as well as (13)C NMR chemical shifts of 4 synthesized TCDPSs have been carried out. The optimized geometries were obtained at the B3LYP/6-311G** level by using the Gaussian 03 program. Meanwhile, related spectral parameters were calculated. In addition, the experimental values were compared with the calculated ones. The results show that the scaled theoretical vibration frequencies are in good accordance with the observations, and computed chemical shifts are consistent with the experimental values.     

Solvation and crystal effects in bilirubin studied by NMR spectroscopy and density functional theory

The open-chain tetrapyrrole compound bilirubin was investigated in chloroform and dimethyl sulfoxide solutions by liquid-state NMR and as solid by (1)H, (13)C, and (15)N magic-angle spinning (MAS) solid-state NMR spectroscopy. Density functional theory (DFT) calculations were performed to interpret the data, using the B3LYP exchange-correlation functional to optimize geometries and to compute NMR chemical shieldings by the gauge-including atomic orbital method. The dependence of geometries and chemical shieldings on the size of the basis sets was investigated for the reference molecules tetramethylsilane, NH(3), and H(2)O, and for bilirubin as a monomer and in clusters consisting of up to six molecules. In order to assess the intrinsic errors of the B3LYP approximation in calculating NMR shieldings, complete basis set estimates were obtained for the nuclear shielding values of the reference molecules. The experimental liquid-state NMR data of bilirubin are well reproduced by a monomeric bilirubin molecule using the 6-311+G(2d,p) basis set for geometry optimization and for calculating chemical shieldings. To simulate the bilirubin crystal, a hexameric model was required. It was constructed from geometry-optimized monomers using information from the X-ray structure of bilirubin to fix the monomeric entities in space and refined by partial optimization. Combining experimental (1)H-(13)C and (1)H-(15)N NMR correlation spectroscopy and density functional theory, almost complete sets of (1)H, (13)C, and (15)N chemical shift assignments were obtained for both liquid and solid states. It is shown that monomeric bilirubin in chloroform solution is formed by 3-vinyl anti conformers, while bilirubin crystals are formed by 3-vinyl syn conformers. This conformational change leads to characteristic differences between the liquid- and solid-state NMR resonances.     

二(β-羟亚胺)二氯化钛配合物的合成及催化乙烯聚合

报道了3个β-羟亚胺配体(2,6-^emPr₂C₆H₃)N＝C(Ph)CH₂CH(Ph)OH(1a), (2,6-^emPr₂C₆H₃)N＝C·(Ph)CH₂C(Ph)₂OH(1b)和(2,6-^emPr₂C₆H₃)N＝C(Ph)CH₂C(C₁₂H₈)OH(1c)及其二(β-羟亚胺)二氯化钛配合物[(2,6-^emPr₂C₆H₃)N＝C(Ph)CH₂CH(Ph)O]₂TiCl₂(2a), [(2,6-^emPr₂C₆H₃)N＝C(Ph)CH₂C(Ph)₂O]₂·TiCl₂(2b)和[(2,6-^emPr₂C₆H₃)N＝C(Ph)CH₂C(C₁₂H₈)O]₂TiCl₂(2c)的合成, 并对其结构进行了表征. 在助催化剂甲基铝氧烷(MAO)作用下, 以化合物2b为主催化剂, 研究了Al/Ti摩尔比、 反应时间、 温度和聚合压力等对乙烯聚合的影响, 发现该催化体系在较宽的反应条件下均可得到很高分子量的聚乙烯, 熔点均在140℃左右. 以化合物2a~2c为主催化剂对乙烯进行催化聚合, 发现在β碳位上取代基的立体位阻对催化剂活性有很大影响. 当化合物2b上引入2个苯基取代基时, 催化剂显示出最佳催化活性.     

Syntheses and characterization of the MF6- (M = As, Sb) salts of the simple trithietanylium PhCS3+ cation and the identity of PhCS3Cl

MF6- (M = As or Sb) salts of a simple derivative of the trithietanylium PhCSSS+, 1, were synthesized for the first time by the reaction of PhCS3Cl and AgMF6 in liquid SO2. 1SbF6 was characterized by IR, FT-Raman, and NMR spectroscopy, elemental analysis, and a preliminary X-ray crystal structure. 1AsF6 was characterized by 1H NMR and FT-Raman spectroscopy. The calculated (MPW1PW91/3-21G* or 6-31G*) geometries, 1H and 13C chemical shifts (MPW1PW91/6-311G(2DF)//MPW1PW91/3-21G*), and vibrational frequencies and intensities (MPW1PW91/6-31G*) were in satisfactory agreement with the observed values. The calculated pi type molecular orbitals of HCSSS+ (MPW1PW91/6-311+G*) and 1 (MPW1PW91/3-21G*) imply that the 6pi-CSSS+ ring has some aromatic character. 1SbF6 undergoes a metathesis reaction with NBu4Cl in liquid SO2 to give PhCS3Cl, which was characterized by vibrational spectroscopy and mass spectrometry. The evidence indicates that PhCS3Cl has the ionic formulation PhCSSS+ Cl- with significant cation-anion interactions in the solid state. ArCSSS+ SbF6- (Ar = 1-naphthyl), 14SbF6, was prepared from ArCS3Cl and AgSbF6, suggesting that the synthesis of MF6- (M = As or Sb) salts of RCSSS+ is potentially general for aryl derivatives. The structure of 14SbF6 was established by 1H and 13C NMR, IR, and FT-Raman spectroscopy, and theoretical calculations gave values in agreement with the experimental data.     

Convenient synthesis and NMR spectral studies of variously substituted <Emphasis Type="Italic">N</Emphasis>-methylpiperidin-4-one-<Emphasis Type="Italic">O</Emphasis>-benzyloximes

Abstract  A series of variously substituted N-methylpiperidin-4-one-O-benzyloximes were synthesized by three different methods. Among them, the direct conversion of 2,6-diarylpiperidin-4-ones into the corresponding oxime ethers (method A) was proved to be better than the other two methods in the sense of good yield, convenience, easy work-up and quick reaction time. All the synthesized compounds are characterized by IR, Mass and NMR (¹H NMR, ¹³C NMR, ¹H-¹H COSY, ¹H-¹³C COSY and HMBC) spectral studies. The conformational preference of the synthesized oxime ethers with/without alkyl and aryl substituents at C-3/C-5 and C-2/C-6 is discussed using the spectral data. The observed chemical shifts and coupling constants suggest that the synthesized oxime ethers adopt chair conformation with equatorial orientation of all the substituents, whereas 1-methyl-3-isopropyl-2,6-diphenylpiperidin-4-one-O-benzyloxime also exists in boat conformation. Based on the NMR data, the effects of oximination on ring carbons and their associated protons and alkyl substituents are discussed. In addition, the effect of NMe group on the 2,6-diarylpiperidin-4-one-O-benzyloximes was also studied. Graphical abstract        

南海海绵Iotrochota ridley化学成分的研究(-)

从中国南海海绵Iotrochotaridley中分离到一种长链甘油醚，其结构经IR，MS，1HNMR，13CNMR，1H－1HCOSY确定为3-十八烷氧基-1，2-丙二醇（鲨肝醇）（Ⅰ）。本文是首次报道该种属海绵的化学成分。     

^1^5N标记邻位芳香羟肟配位体的核磁共振研究

利用稳定同位素的磁性和质量同位素效应已成为研究有机结构化学的重要手段。我们为研究部位芳香及其芝渡金属如Cu(Ⅱ),Ni(Ⅱ),Co(Ⅱ),Fe(Ⅱ)配合物的光     

Complete 1H, 13C and 15N NMR assignment of tirapazamine and related 1,2,4-benzotriazine N-oxides

1H, 13C and 15N NMR measurements (1D and 2D including 1H--15N gs-HMBC) have been carried out on 3-amino-1, 2,4-benzotriazine and a series of N-oxides and complete assignments established. N-Oxidation at any position resulted in large upfield shifts of the corresponding N-1 and N-2 resonances and downfield shifts for N-4 with the exception of the 3-amino-1,2,4-benzotriazine 1-oxide in which a small upfield shift of N-4 was observed. Density functional GIAO calculations of the 15N and 13C chemical shifts [B3LYP/6-31G(d)//B3LYP/6-311+G(2d,p)] gave good agreement with experimental values confirming the assignments. The combination of 13C and 15N NMR provides an unambiguous method for assigning the 1H and 13C resonances of N-oxides of 1,2,4-benzotriazines.     

Theoretical Studies on the Infrared Vibrational Spectra ,Thermodynamic Properties and Nuclear Magnetic Resonance Spectra for Polynitro-1,3-bishomopentaprismanes

Based on the optimized molecular geometries at the DFT‐B3LYP/6‐31G?? level, IR spectra, thermodynamic functions, as well as ¹³C and ¹H NMR chemical shifts, were obtained and discussed for polynitro‐1,3‐bishomo‐pentaprismanes (PNBPP). The comparison of the calculated IR frequencies and NMR chemical shifts showed considerable agreements with the available experimental results. IR regions, ¹³C and ¹H NMR chemical shifts of PNBPP were assigned. The relationships of the thermodynamic functions with temperature and the number of nitro groups were discussed, and it was found that the latter showed a good group additivity rule. These calculated data and discussions would be helpful for the further study of PNBPP.