共查询到20条相似文献,搜索用时 31 毫秒
1.
Burgueño-Tapia E López-Escobedo S González-Ledesma M Joseph-Nathan P 《Magnetic resonance in chemistry : MRC》2007,45(6):457-462
From the hexane extracts of Senecio sinuatus roots, the new 3beta-angeloyloxy-6beta-hydroxyeremophil-1(10)-en-8beta,12-olide (3), along with the known compounds 3beta-angeloyloxy-6beta-hydroxyeremophil-1(10)-ene (1), 3beta-senecioyloxy-6beta-hydroxyeremophil-1(10)-ene (2), and 3beta-angeloyloxy-6beta,8alpha-dihydroxyeremophil-1(10)-en-8beta,12-olide (4), were isolated. Complete 1H and 13C NMR chemical shift assignments of 1-4 were achieved using one- and two-dimensional NMR techniques, including gHMQC and gHMBC experiments. A Monte Carlo search, followed by B3LYP/6-31G*DFT calculation, provided the theoretical conformations of the eremophilane rings, which were in agreement with results derived from 1H-1H NMR coupling constant analysis, and confirmed by NOESY experiments. 相似文献
2.
Chazel C Ménétrier M Croguennec L Delmas C 《Magnetic resonance in chemistry : MRC》2005,43(10):849-857
A series of Li1-zNi1+zO2 materials have been synthesised by the coprecipitation route. An X-ray diffraction study was carried out on these materials using the Rietveld method to determine the departure from the ideal stoichiometry z, which ranges from 0 to 0.138. The actual Li/Ni ratio was also checked by chemical analyses using inductively coupled plasma (ICP) for each sample. The stoichiometric sample (z approximately 0) was obtained using a 15% Li excess. (6/7)Li NMR results from LiNiO2 (z approximately 0) show that the asymmetric shape of the NMR signal is due to anisotropy. Calculations give evidence that the paramagnetic dipolar interaction from the electron spins carried by Ni is anisotropic but does not completely explain the experimental anisotropy. (6)Li MAS NMR (magic angle spinning NMR) experiments and temperature standardisation NMR measurements unambiguously assign the isotropic position at +726 ppm. The static-echo NMR spectra of the non-stoichiometric Li1-zNi1+zO2 phases also exhibit an asymmetric shape whose width increases with the departure from the ideal stoichiometry z. (6/7)Li static and MAS NMR show that the 2zNi(2+) ions thus formed modify the dipolar interaction within the materials and also affect the Fermi contact interaction, since a distribution of Li environments is observed using (6)Li NMR for non-stoichiometric samples. 相似文献
3.
Complete assignments of 1H and 13C NMR data for seven arylnaphthalide lignans from Justicia procumbens 总被引:1,自引:0,他引:1
Three new arylnaphthalide lignans named 6'-hydroxy justicidin A (1), 6'-hydroxy justicidin B (2) and 6'-hydroxy justicidin C (3) have been isolated from the whole plant of Justicia procumbens, together with four known ones, neojusticin A (4), chinensinaphthol methyl ester (5), isodiphyllin (6) and taiwanin C (7). The complete assignments of 1H and 13C NMR chemical shifts for the new lignans and the 13C NMR chemical shifts for the known lignans were obtained for the first time by means of 2D NMR techniques, including HSQC and HMBC. 相似文献
4.
Pezdirc L Bevk D Groselj U Meden A Stanovnik B Svete J 《Journal of combinatorial chemistry》2007,9(4):717-723
Combinatorial solution-phase cycloadditions of (1Z,4R*,5R*)-4-benzoylamino-5-phenylpyrazolidin-3-on-1-azomethine imines 3 to beta-keto esters 4 afforded a library of 26 bicyclic pyrazolidinones 5 in 6-89% yields and in 14-100% de. All products were isolated in >90% purity according to 1H NMR, and 25 of them were analytically pure. The structures of cycloadducts were confirmed by NMR and X-ray diffraction. Most of the products were isolated as mixtures of the major (1S*,2S*,3R*,5R*,6R*)-epimers 5 and the minor (1R*,2S*,3R*,5R*,6R*)-epimers 6. Epimerization of cycloadducts 5/6 at the anomeric position 1 in solution was confirmed by 1H NMR. 相似文献
5.
A chiral enolate aggregate 1 containing a lithium enolate and a chiral lithium amide was systematically investigated by various NMR techniques. (1)H and (13)C DOSY at 25 and -78 degrees C provide its solution structure, aggregation number, and formula weight. Multiple 2D (6)Li NMR techniques, such as (6)Li-(6)Li EXSY, (6)Li-(1)H HOESY, were utilized to investigate its stereochemical structure. The configuration of the enolate in complex 1 was confirmed by (6)Li-(1)H HOESY and trapping with TMS-Cl. A unique (6)Li-(1)H coupling through the Li-N-C-H network was observed. This scalar coupling was corroborated by (6)Li-(1)H HMQC, deuterium labeling experiments, and selective (1)H decoupling (6)Li NMR. The stereostructure of 1 provides a model for the origin of enantioselectivity of chiral lithium amide-induced enolate addition reactions. 相似文献
6.
The complexation of sulfur hexafluoride (SF(6)), a highly potent greenhouse gas, by cucurbit[6]uril (CB) was studied at various temperatures in Na(2)SO(4) aqueous solutions by (19)F and (1)H NMR. CB shows a remarkable affinity for SF(6), suggesting that it is a suitable molecular container for the design of materials tailored for SF(6) trapping. At 298 K, the equilibrium constant characterizing the inclusion of SF(6) by CB is 3.1 x 10(4) M(-1) and the residence time of SF(6) within the CB cavity is estimated to be of the order of a few seconds. The enthalpic and entropic contributions to the free energy of encapsulation were determined and are discussed. This work also reports on the interest of SF(6) in the framework of the spin-spy methodology. The advantages and drawbacks of solution-state (19)F NMR of SF(6) with respect to (129)Xe NMR are discussed. SF(6) comes forward as a versatile and informative spin-spy molecule for probing systems in solution because its detection limit by (19)F NMR reaches the micromolar range with standard equipment and because quantitative integral measurements, relaxation time measurements, and demanding experiments, such as translational diffusion coefficient measurements, are easily carried out in addition to chemical shift measurements. Solution-state (19)F NMR of SF(6) emerges as a promising alternative to (129)Xe NMR for probing cavities and for other applications relying on the encapsulation of an NMR active gaseous probe. 相似文献
7.
Multinuclear and multidimensional NMR spectroscopy have shown that lithium (S)-N-isopropyl-O-methyl-valinol (1-[6Li]) exists in a mixed 2:1 complex with nBu[6Li], (1-[6Li])2/nBu[6Li], in non-coordinating solvents such as hexane or toluene. A 6Li,1H-HOESY NMR spectrum indicates that the complex is a cyclic trimer with a large distance between the di-coordinated lithium and the carbanion of nBu[6Li]. Such arrangements are present in the solid state as previously reported by Williard and Sun. The exchange of lithium atoms within the trimer is slow at -33 degrees C. The exchange barrier (deltaG++) was determined to be 14.7 kcal x mol(-1) from quantitative 6Li,6Li-EXSY spectra. Addition of diethyl ether results in the formation of mixed dimers of (1-[6Li])/nBu[6Li], tetramers of nBu[6Li], and homodimers (1-[6Li])2. The apparent equilibrium constant of the mixed dimer was determined from the 6Li NMR integrals as K = 7. 相似文献
8.
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. 相似文献
9.
我们以1,4-二正丙氧基-2,5-双甲氧甲基苯为原料用对甲苯磺酸为催化剂在二氯甲烷中制备了1,4-双正丙氧基柱[5]芳烃, 1,4-双正丙氧基柱[6]芳烃和1,4-双正丙氧基柱[7]芳烃. 我们用氢谱, 碳谱和质谱对它们进行了表征. 它们有不同的氢谱却有相似的碳谱. 对比它们的空腔尺寸, 柱[5]的内径大约是4.6 Å, 与葫芦脲[6]及α-环糊精类似. 柱[6]的内径大约是6.7 Å, 与葫芦脲[7]及β-环糊精类似. 柱[7]的内径大约是8.7 Å, 与葫芦脲[8]及γ-环糊精类似. 我们用正辛基三乙基六氟磷酸铵盐作为模型客体研究了它们之间的主客体络合. 柱[5]与之有微弱的络合, 柱[6]显示了良好的络合, 而柱[7]与之没有络合. 相似文献
10.
小果博落回对照物质及其核磁共振氢谱指纹图的创建 总被引:8,自引:0,他引:8
采用规范化的程序获取6个不同来源小果博落回样品的对照物质(CSPD)及其^1H NMR图谱;从小果博落回CSPD中分得6个单体成分,其结构分别被鉴定为二氢血根碱(1)、二氢白屈菜红碱(2)、6-甲氧基二氢血根碱(3)、6-甲氧基二氢白屈菜红碱(4)、齐墩果酸(5)和原阿片碱(6)。通过各单体化合物的^1H NMR图谱与CSPD的^1H NMR图谱的对比研究,实现了小果博落回的^1H NMR指纹图的解析。研究结果表明:6个不同来源的小果博落回样品,其^1H NMR指纹图有很好的重现性和高度的特征性,并主要显示以上生物碱类成分的特征共振信号,可做为其基源鉴定的参考。 相似文献
11.
12.
Katritzky AR Akhmedov NG Wang M Rostek CJ Steel PJ 《Magnetic resonance in chemistry : MRC》2004,42(7):648-658
The 1H and 13C NMR spectra of compounds 1-11 and 16-22 in CDCl3 and DMSO-d6 solutions allowed structural assignment to regioisomers 1/5 and 2/6 and their regioselective cyclization products 16-18 utilizing one- and two-dimensional NMR techniques (APT, DEPT, NOE difference, COSY, NOESY, HETCOR and gHMQC, gHMBC). Temperature-dependent 1H NMR spectra of 8-anilino-5-(4-methyl-2-pentyl)-2,3-dihydro-1,5-benzothiazepin-4(5H)-one (18) indicated a free energy of activation (deltaG++) of ca 17 kcal mol(-1) for interconversion between rotamers. The 1H and 13C NMR spectra of 20 and 22 containing two chiral centers exhibit duplication of several signals, indicating the existence of two diastereomeric forms. The structure of 4 was unambiguously confirmed by x-ray crystallography. 相似文献
13.
6-(Bromomethyl)-4-methoxy-5,6,7,8-tetrahydropyrido[3,2-d]pyrimidin-2-ol(compound 9) was synthesized from 6-methylpyrimidine-2,4-diol(compound 1) through the crucial steps of 6-methyl alkylating and intramolecular cyclization. The assignment of the structure of compound 9 was performed by its spectral data, 1H NMR, 13C NMR, HMBC, and HRMS spectra. 相似文献
14.
Jean A Fuller-Stanley James H Loehlin Kimberly A Bolin Genevieve Fairbrother Fausta Nazaire 《The Journal of organic chemistry》2002,67(1):27-31
1-Oxa-3S,4S,6R-triphenyl-2-cyclohexanone and its enantiomer were synthesized, and the structure was determined by NMR and X-ray crystallography. The X-ray crystal structure showed that the delta-lactone adopts a boat conformation in the solid. The X-ray data showed a shortened C-O bond between the carbonyl carbon and the ether oxygen, consistent with delocalization involving the ester group. (1)H and (13)C NMR measurements in acetone-d(6) showed that the lactone is biased in favor of a boat conformation. In the less polar solvent chloroform-d(1), changes in the (1)H NMR coupling constants indicate a shift in the equilibrium in favor of a less rigid twist-boat conformation. The IR absorption of the lactone carbonyl at 1740 cm(-)(1) would suggest a half-chair conformation inconsistent with the dominance of the boat forms shown by NMR and X-ray. 相似文献
15.
16.
Preparation of Novel Side-chain Pseudopolyrotaxanes Consisting of Cucurbituril[6] and Polyamine Salts 总被引:1,自引:0,他引:1
Zhao Sheng HOU Ye Bang TAN Kimoon KIM Qi Feng ZHOU 《中国化学快报》2005,16(8):1031-1034
Pseudorotaxane monomer (VBCB) containing cucurbitutil[6] (CB[6]) and N^1-(4-vinylbenzyl)-1,4-diaminobutane dihydrochloride (VBDADC) is obtained by self-assembly of cucurbituril[6] with VBDADC in water and then polymerized using potassium persulfate (KPS) as initiator to give novel water-soluble side-chain cucurbituril[6]-based pseudopolyrotaxane(PVBCB). The chemical structures of PVBCB, VBCB and VBDADC are confirmed by ^1H NMR,^13C NMR spectra and elemental analysis. In VBCB, CB[6] is localized aliphatic group of the side chain and the molar ratio of CB[6] to VBDAC is 1:1 . 相似文献
17.
The 1H and 13C NMR spectra of 3-azabicyclo[3.3.1]nonanes with various oxygenated substituents at C-6 were assigned using 1D (DEPT) and 2D (COSY, HSQC, HMBC, NOESY) experiments. Close examination of this NMR data details the effects of substitution and stereochemistry at C-6 in these compounds. 相似文献
18.
Parent 1-silaadamant-1-yl (1+) and a series of mono-beta-silyl-substituted- (2-Me+, 2-F+, 2-Cl+, 2-Br+), bis-beta-silyl-substituted- (3-Me+), and tris-beta-silyl-substituted (4-Me+)-1-silaadamant-1-yl cations were studied by the DFT method at the B3LYP/6-31G(d,p) level and by GIAO NMR at the B3LYP/ 6-31G(d,p)//B3LYP/6-31G(d,p) level. The geometries, relative energies, NMR chemical shifts, and charge distribution in the bridgehead silylium ions are discussed and compared. The magnitude of the beta-silyl effect (the Si-C-Si+ hyperconjugation) is gauged as a function of structure. Related model studies on the silabicyclo[2.2.2]octyl (5+, 6+, 5a+, and 6a+), silanorbornyl (7+ and 8+), and silacyclohexyl cations (9+ and 10+) were carried out in which the effect of beta-silyl substitution on geometry, stability, and NMR chemical shifts was probed. The acyclic model Me3Si-CH2-Si+(Me)2 (11+) was used to gauge the influence of the twist angle between the p-orbital at Si+ and the C-Si bond on relative stability and on the changes in the 29Si NMR chemical shifts. Finally, interaction of 1+ with H2O and MeOH and 2-Me+ with H2O was also examined. The resulting optimized structures (12+, 13+, and 14+) and the computed NMR chemical shifts are most compatible with the formation of silaoxonium ions. 相似文献
19.
Alver O Parlak C Senyel M 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,67(3-4):793-801
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. 相似文献