A 1H-NMR Spectroscopic Investigation of the Conformation of the Acetamido Group in Some Derivatives of N-Acetyl-D-allosamine and -D-glucosamine

The population of the conformations obtained by rotation around the C(2)? N and the N? C(O) bonds of AllNAc, GlcNAc, and GlcNMeAc derivatives was investigated by ¹H-NMR spectroscopy. The AllNAc-derived α-D -and β-D -pyranosides 4–7 , the AllNAc diazirine 16 , and the GlcNAc-derived axial anomers α-D - 8–10 prefer the (Z)-anti-conformation. A significant population of the (Z)-syn-conformer in the (Z)-syn/(Z)-anti-equilibrium for the equatorial anomers β-D - 8–10 and the GlcNAc diazirine 17 was evidenced by an upfield shift of H? C(2), downfield shifts of H? C(1) and H? C(3), and by NOE measurements. The population of the (Z)-syn-conformation depends on the substituent at C(1) and is highest for the hexafluoroisopropyl glycoside. The population of the (Z)-syn-conformation of β-D - 14 decreases with increasing polarity of the solvent, but a substantial population is still observed for solutions in D₂O. Whereas the α-D -anomers of the hemiacetal 22 and the methyl glycoside 21 prefer the (Z)-anti-conformation in D₂O solution, the corresponding β-D -anomers are mixtures of the (Z)-anti-and (Z)-syn-conformers. The diazirine 17 self-associates in CD₂Cl₂ solution at concentrations above 0.005M at low temperatures. The axial anomers of the GlcNMeAc derivatives α-D - 26–28 are 2:1 to 3:1 mixtures of (Z)-anti-and (E)-anti-conformers, whereas the corresponding β-D -glycosides are ca. 1:3:6 mixtures of (Z)-syn-, (Z)-anti-, and (E)-anti-conformers.     

Piperaceae Alkaloids: Part I. Structure of piperstachine; 13C- and 1H-NMR. Studies

From the stem of Piper trichostachyon C. DC. a new alkaloid designated piperstachine (VII) has been isolated. Its structure is derived on the basis of spectral data and synthesis of hexahydropiperstachine (X).     

Syntheses and 1H-NMR Studies on Mucin-Type Sugars Chirally Deuterated at the C-6 Position

Abstract

1-O-Methyl analogs of mucin oligosaccharide components, D-GalNAc (1a and 1b). β-D-Galp-(1-3)-D-GalNAc (2) and β-D-Galp(1-3)-[β-D-GlcNAc-(1-6)]-D-GalNAc (3) in which the H-6proS proton was selectively replaced by a deuterium, were synthesized to study the solution conformations about the C5-C6 fragments by ¹H-NMR spectroscopy. The study revealed the preference of the gt-conformer for these sugars.     

13C- and 1H-NMR. Studies on the Configuration of Tricarbonyliron Complexes of Oxa- and Aza[4.4.3]propellanes

The configurations of a series of mono- and bis-Fe(CO)₃ complexes of 12-oxa[4.4.3]-propella-2,4,7,9-tetraene ( 1 ) and of 11,13-dioxo-12-methyl-12-aza[4.4.3]propella-2,4,7,9-tetraene ( 7 ) as well as of a trienic aza-propellane complex have been studied in solution by ₁₃C- and ₁H-NMR. spectroscopy. Praseodymium-induced ₁₃C-shifts of the metalcarbonyl carbon atoms and of the central carbon atom of the complexed diene systems are particularly sensitive and useful to prove exo- or endo-configuration of the tricarbonyliron ligand. In addition, H,H- and C,H-coupling constants of the complexes and parent compounds are reported and discussed.     

An 1H-NMR. Spectroscopic Study of Alloxazines and Isoalloxazines

¹H-NMR.-spectra of a series of alloxazines and isoalloxazines and certain cationic derivatives were investigated (Tab. 2 and 5). Unequivocal assignment of all resonance signals was achieved in some compounds by selective deuteriation also by double resonance technique. The coupling constants were verified by computer simulation. Considerable enhancement of the signals due to H-C(9) and H-C(6) is found on decoupling of H₃C-C(7), H₃C-C(8) and H₃C-N(10), resp. These results are compared with those obtained with FAD. The methyl resonance signal of the H₃C-C(7) compounds give doublets due to coupling with H-C(6). The difference in chemical shifts observed upon successive formal introduction of methyl groups into the benzene nucleus of (iso)alloxazines indicates that the molecule becomes less planar thereby. The pyrimidine ring of (iso)alloxazines does not contribute to the ring current except by indirect effects via the carbonyl groups. The experimental data are compared with published MO calculations and discussed.     

MC-determination in elastomers by 1H-NMR relaxation and 2H-NMR spectroscopy

We show how ¹H–NMR transversal relaxation and ²H–NMR spectroscopy can be used for the determination of the number average molecular mass M_C in typical elastomers at temperatures well above the glass transition temperature. M_C-results of the different NMR methods are compared among one another and with M_C-results of other common independent methods. Moreover, the NMR measurements provide a number of additional useful parameters: correlation times, portions of dangling chain ends and of sol molecules, molecular order.     

核磁共振氢谱测定盐酸浓度的探讨

探讨了用核磁共振氢谱检测盐酸浓度的方法。使用简易核磁共振氢谱直接检测无氘代溶剂参与的HCl溶液,通过合适的锁场、匀场及参数设置,能获得满意的氢谱。对系列已知浓度的HCl溶液进行检测,以含1,4-二氧六环的毛细管内标做参比,得到化学位移在7.99ppm(浓HCl)至4.67ppm(纯水)之间,作图获得标准曲线,化学位移与HCl浓度呈良好的线性关系。应用标准曲线对HCl的挥发度进行探讨,动力学实验显示在50℃与25℃时,浓HCl分别在7d与25d达到稳定的浓度,约为7mol·L-1。     

1H-NMR study of polyisoprenes

¹H-NMR spectra of polyisoprene were assigned using polymers of isoprene-1,1,4,4-d₄, isoprene-1,1,5,5,5-d₅, and isoprene-4,4-d₂ polymerized with various catalysts. The methylene-proton signal at 2.1 ppm in cis-1,4 - and trans-1,4-polyisoprenes was divided into H₄- and H₁-proton signals; H₄ resonated at 2.21 ppm in both cis-1,4 and trans-1,4 units whereas H₁ resonated at 2.05, 2.21, and 2.15 ppm. Splitting due to the dyad sequences of 1,4 and 3,4 units was apparent. The methine-proton (H₃) in a 3,4 unit showed a broad peak centered around 1.5 ppm in C₆D₆. The overlapping of this signal with the methyl-proton signals at 1.73 and 1.63 ppm resulted in some uncertainty in the determination of the microstructure of polyisoprene which contained a considerable amount of 3,4 unit.     

Computer-Assisted Structural Interpretation of 1H-NMR. Spectral Data

Interactive computer programs for the establishment and maintenance of a ¹H-NMR. data base, the prediction of ¹H-NMR. shifts and the rank-ordering of structural candidates based on comparison between observed and predicted spectra are presented. The programs take into account configuration, at stereocenters and double bonds, as well as diastereotopy. We demonstrate how, for purposes of structure elucidation, these new programs can be linked to the GENOA and STEREO programs.     

环酮的构象研究进展

综述了30多年来环酮（n=8，9，10，11，12，13，14，15，16）及对称的偶数 环二酮（n=8，10，12，14，16，18，20，22，24，26）的构象研究进展。     

13C- and 1H-NMR. Assignments for colchicine derivatives

The ¹³C-NMR. spectra of a number of colchicine derivatives are given comprising examples of the normal series ( 4→10 ), iso series ( 11→16 ) and colchicine series ( 17 ), which were either reported in the literature or obtained by partial synthesis or degradation reactions. The ¹³C-NMR. assignments were made by comparisons with known compounds and selective single-frequency offresonance decoupling experiments. Selective proton decoupling experiments have also allowed assignments of the H —C(11) and H —C(12) protons of the iso and colchicine series.     

HPLC and 1H-NMR Studies of Alkaline Hydrolysis of Some 7-(Oxyiminoacyl)cephalosporins

Alkaline hydrolysis (pH 10.5) of the three 7-(oxyiminoacyl)cephalosporins 1a–c (cefuroxime, ceftazidime, and ceftriaxone) was studied at 37° using HPLC and ¹H-NMR techniques. The 7-epicephalosporin 2 , the 3-methylidene compound 3 , and the 6-epimer 4 of the 3-methylidene compound 3 were identified for each cephalosporin as the major degradation products under the conditions used; ceftazidime ( 1b ) yielded also the Δ²-isomer 5b (Scheme 1). A kinetic scheme was developed to account for the production of these compounds, and the different kinetic constants involved in the process were calculated. The experimental results show that the presence of a pyridinio group at position C–C(3) favours the appearance of the Δ²-isomer, which was detected mainly in cephalosporins bearing an ester function at C(4). The presence of an oxyimino group at C? CONH? C(7) facilitates epimerization at C(7) (→ 2 ), whereas that of an electron-withdrawing group at C? C(3) results in a increased formation constant for the 3-methylidene compound 3 . The 3-methylidene compounds 3a–c produced by the three cephalosporins on cleavage of the β-lactam ring all underwent epimerization at C(6) to yield the corresponding 6-epimer 4 .     

Homonuclear Overhauser 1H-NMR. Experiments on the Carotenoid Pigments Lycopene and Prolycopene

The recently proposed structure of the carotenoid pigment prolycopene as the 7,9,7′,9′-tetra-cis isomer of lycopene has been unambiguously confirmed by a series of homonuclear Overhauser ¹H-NMR. experiments at 270 MHz. Comparative measurements are reported for lycopene.     

环化鸟苷酸双聚体堆积构象的研究

本文应用分子轨道方法和改进的多原子分子间相互作用势函数研究了环化鸟苷酸双聚体当以顺式构象形成的三种可能堆积模式(面对面、背对背、面对背)的构象的稳定与堆积间距和鸟苷取向的关系。研究结果表明当环化鸟苷酸取面对面的堆积模式且其堆积间距为4.15,堆积的旋转角为115°时环化鸟苷酸双聚体的堆积构象是最稳定的。研究结果还表明对于环化鸟苷酸双聚体堆积构象的旋转角取向的最优位置,主要取决于它们的分子间相互作用势的静电能贡献;它的堆积间距的最优位置则主要取决于它们的极化能、色散能和排斥能的贡献。     

Angular dependence of 1H-NMR and 2H-NMR spectra of water absorbed in cellulose film

¹H-NMR and ²H-NMR spectra of water (H₂O and D₂O) absorbed in Visking cellulose tubing have been observed as a function of the angle Θ between the film surface and the magnetic field. ¹H-NMR spectra show broad lines, and the chemical shift and the linewidth depend on Θ. From the angular dependence of the chemical shift, the anisotropic volume diamagnetic susceptibilities of the film are determined, i.e., χ_∥ in the direction longitudinal to the tubing (stretched direction) is 0.43 ppm, and χ_⊥ in the transverse direction is 0.57 ppm. The different values of χ_∥ and χ_⊥ afford an evidence of the anisotropy of the film. ²H-NMR spectra of D₂O absorbed in the film show quadrupole splitting which also depends on Θ. The angular dependences of the linewidth (¹H-NMR) and the quadrupole splitting (²H-NMR) indicate that the H? H axes of the water molecules have a tendency to orient in the direction longitudinal to the film surface.     

1H-NMR spectra of some ditriazolyls and ditriazolyalkanes

Summary The proton magnetic resonance spectra of 12 azoles were measured in neutral and acidic solvents. The protonation shifts observed by comparison of the spectra inDMSO-d ₆ andTFA were attributed to an amidinium type resonance of the resulting cations. The synthesis and characterization of the azoles are also discussed.

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¹H-NMR-Spektren einiger Ditriazolyle und Ditriazolylalkane

Zusammenfassung Es wurden die¹H-NMR-Spektren von 12 Azol-Verbindungen in neutralem (DMSO-d ₆) und azidischem (TFA) Lösungsmittel gemessen und die chemischen Verschiebungswerte verglichen. Der Unterschied beider Werte beruht höchstwahrscheinlich auf einer Amidinium-Typ Resonanz der im azidischen Bereich entstandenen Kationen. Im Rahmen dieser Arbeit wurden 12 Azol-Verbindungen synthetisiert und beschrieben.

     

Functional derivatives of thiophene. I. Synthesis and 1H-NMR spectra in the 2-aminothiophene series

The preparation of 2-amino-5-nitrothiophene, 2-formamido-5-nitrothiophene, 2-acetamido-5-nitrothiophene and 2-t-butyloxycarbonylamino-5-nitrothiophene are described. Abnormal values of the coupling constants J_3.4 had been observed in the ¹H-nmr spectra of compounds obtained.