Automatic assignment of 13C NMR signals based on the Karplus-Pople equation

A modified version of the method of automatic assignment of ¹³C NMR spectra, based on the Karplus-Pople equation is applied to six substituted benzenes. The results are the same as in the case of simple ¹³C chemical shift/charge density linear relationship previously used: -XR substituted aryls (XO, RH, CH₃, CH₂CH₂OH) yield good correlation and correct automatic assignment, while -CH₂CH₂Y substituents (YH, OH, NH₂) yield poor correlation and incorrect assignment.     

Aufkl?rung der 1H- und 13C-NMR-spektren sowie der kristallstruktur unges?ttigter glycosylphosphonate und konformationsberechnungen an modellen1

By application of a modified LAOCN-3 program a complete elucidation of the ¹H NMR spectra of 2,3-unsaturated glycosyl phosphonates 1–5 could be achieved. The exactly determined ⁿJ(H, H) and novel ⁿJ(C, P) coupling constants are discussed, and permit a conclusive deduction of the conformations. The ¹³C NMR spectra of 1 to 6 can be fully interpreted. By a close inspection of chemical shifts as well as ¹J(C-H) and ⁿJ(C, P) coupling constants the conformational assignment is supported. For all the derivatives the correlations ¹J(C-1,H_e)>¹J(C-1, H_a) and ¹J(C-1, P_e) >¹J(C-1, P_a) can be used for the assignment of anomers. The crystal structure of 1 is in accordance with this assignment of anomers and displays an unexpected conformation. Calculations by MINDO-3 in resembling model compounds serve to elucidate such conformative effects.     

13C NMR spectra of some furocoumarins

¹³C NMR spectra of some naturally occurring furocoumarins and derivatives have been examined. The assignment of chemical shifts for all the C atoms has been achieved by using techniques recently reported by Bose et al.     

13C-{1H} NMR spectra of episulphide copolymers

Ethylene sulphide-isobutylene sulphide and propylene sulphide-isobutylene sulphide copolymers have been prepared using anionic catalysts and investigated by ¹³C-{¹H} NMR spectroscopy. The carbon-13 NMR spectra are assigned in terms of diad and triad sequences. There is discussion of the effects of mono- or dimethyl substitution in the α, β, γ or δ positions on the chemical shift of the main chain carbon atoms. It has also been shown that for isobutylene sulphide, as for propylene sulphide, under the influence of an anionic catalyst, there is a normal ring opening only at the primary carbon atom.     

Qualitative and quantitative characterization of a complex mixture of hexylbenzenes by 13C nuclear magnetic resonance and gas chromatography-mass spectrometry

Summary A considerable amount of byproducts is formed in the production of isopropylbenzene (cumene). Recently, a distillation fraction of these byproducts became commercially attractive which justified its compositional analysis. All the signals in the complex ¹³C nuclear magnetic resonance (NMR) spectrum of this material have been assigned. The mass spectra of the individual constituents were recorded by the application of capillary gas chromatography-mass spectrometry. The data obtained with both analytical techniques revealed that the product is composed of a complex mixture of 3 isomeric diisopropylbenzenes and 10 different hexyl-substituted benzenes. The mass spectra and carbon-13 NMR chemical shift data of most of the compounds presented here have not been previously reported. NMR data of all possible butyl- and a number of pentyl-substituted benzenes are included in this report for assignment purposes. Quantitative studies on this material and some of its distillation fractions by ¹³C NMR and gas chromatography enabled the assignment of individual peaks in the gas chromatogram.

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Qualitative und quantitative Charakterisierung eines komplexen Gemisches von Hexylbenzolen durch ¹³C-NMR und GC/MS

     

13C NMR spectra of some coumarins of Haplophyllum obtusifolium

Coumaris ofHaplophyllum obtusifolium Ledeb. — obtusinin, capensin, and fraxetin 7-O--D-glucopyranoside — have been investigated by¹³C NMR spectroscopy. Several distinctive features of their NMR spectra have been observed. A complete assignment of the¹³C NMR spectra of these coumarins has been made and their structures have been confirmed.Institute of the Chemistry of Plant Substances, Uzbek SSR Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 796–799, November–December, 1987.     

Effects of chemical shift anisotropy and 14N coupling on the 1H and 195Pt nuclear magnetic resonance spectra of platinum complexes

Broadening of the ¹⁹⁵Pt satellites in the ¹H NMR spectrum of trans-Pt(ethene)(2-carboxy-pyridine)Cl₂ at high field arises from relaxation of ¹⁹⁵Pt via the chemical shift anisotropy mechanism. We also demonstrate that well-resolved ¹⁴N-¹⁹⁵Pt couplings can be observed in ¹⁹⁵Pt NMR spectra of Pt(II) and Pt(IV) amine complexes, including anti-tumour agents, at elevated temperature where scalar coupling contributions to ¹⁹⁵Pt relaxation are much reduced.     

Effects of external electric fields on 1H, 19F,and 14N NMR spectra of 2, 4, 6-trifluoronitrobenzene

When a polar liquid is subjected to an electric field, the dipoles obtain a small average orientation. At sufficiently high field strengths direct spin—spin dipolar and quadrUpolar electric field interactions may modify the NMR spetrum.NMR electric field experiments are reported for the proton, fluorine, and nitrogen NMR spectra of neat 2, 4, 6-trifluoronitrobenzene. The observed alignment values are smaller than those predicted on the basis of Onsager's theory.The ¹⁴N quadrupole coupling constant as been deduced from a comparison of the qUadrupolar and dipolar electric field effects.An upper limit of the absolute value of the anisotropy of the para-¹⁹F chemical shift has been inferred from the absence of a detectable displacement of the resonance on application of an electric field.     

Pyrrolizidine alkaloids necine bases: II. Conformational analysis of free bases

Molecular mechanics calculations were applied to the conformational analysis of two diasteroisomers, the pyrrolizidine alkaloids (PAs) retronecine and heliotridine. The application of reoptimized parameters for H bonding corrected the tendency of MM3(92) calculations to give unrealistic H(DOTTED BOND)O distances for intramolecular OH interactions occurring in both diasterisomers. Inversions in the H-bond direction of exo-retronecine and in the relative stability of heliotridine endo–exo conformers were also observed with the application of the new parameters. A set of probable conformers was obtained for each diasterisomer, based on conformational and Boltzmann population analysis. Only exo-puckered conformers were found in the retronecine set, whereas both exo- and endo-puckered conformers were obtained for heliotridine. Transition state conformations supplied arguments supporting the design of models for H-bond interconversion in the case of exo-retronecine and for the exo–endo interconversion of heliotridine. Reactivity behaviors and ¹H-NMR data of both diasterisomers were elucidated in light of the theoretical results. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1853–1861, 1998     

1H and13C NMR spectra and the structure of a new coumarin, C-glycoside dauroside D, fromHaplophyllum dauricum

On the basis of chemical transformations,¹H and¹³C NMR spectra, the structure of dauroside D isolated fromHaplophyllum dauricum has been established as 6-C--D-glucopyranosyl-5,7-dihydroxycoumarin. Some interesting features of the¹H NMR spectra of its acetate have been reported and an assignment of the signals in its¹H and¹³C NMR spectra has been made. Dauroside D is the first natural coumarin C-glycoside.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 441–445, July–August, 1983.     

人宫颈癌细胞(Hela)内的31P核磁共振研究

建立了无损伤性³¹P NMR研究细胞内物质的实验方法, 并对人宫颈癌细胞(Hela)的³¹P NMR谱中含磷小分子代谢物的谱峰进行了分析; 细胞内无机磷(Pi)的化学位移对pH非常敏感, 通过测定其化学位移可间接确定细胞内的pH, Hela细胞内Pi峰的化学位移为5.88±0.01 (n＝3), 计算得到细胞内 pH值为7.05±0.01; 通过测量Hela细胞的³¹P NMR谱中ATP的α磷和β磷及γ磷的化学位移差值, 得出Hela细胞内Mg^2＋与ATP结合的复合物MgATP和整个ATP量的比值, 计算得到Hela细胞内游离Mg^2＋浓度为(253.3±0.13) mmol/L (n＝3), 与其它分析方法相比, ³¹P NMR测定细胞内游离Mg^2＋浓度具有对细胞样品无损伤的优点.     

13C and 1H NMR spectra of monosubstituted ferrocenes containing a chiral centre in the substituent

The ¹³C-{¹H} and ¹H NMR spectra of ferrocenyl chalkones (β-benzoylvinylferrocene add cinnamoylferrocene) and their iron carbonyl complexes were recorded. Splitting of the resonances of both α- and β-substituted cyclopentadienyl ring atoms was found in ¹³C-{¹H} NMR spectra of all complexes. In ¹H NMR spectra splitting of the resonances of the substituted cyclopentadienyl ring α-protons was detected only in the case of (cinnamoylferrocene)iron tricarbonyl. The splitting effect mentioned can be due to thesochsochronism (magnetic nonequivalence) of all carbon and hydrogen nuclei because of the iron carbonyl fragment coordination oauses the substituent to become the chiral group. The coordination of iron carbonyl group results in a reduction of the conjugation in the α,β-unsaturated ketone system. This phenomenon is discussed on the basis of ¹³C-{¹H} and ¹H NMR data.     

1H and13C NMR spectra of biologically active compounds

The¹H and¹³C NMR spectra of diols of the hexachlorobicycloheptene and-heptadiene series, and also of the diacetates and sulfites corresponding to them, have been investigated. Criteria for the stereochemical assignment of the compounds mentioned on the basis of chemical shifts and spin-spin coupling constants have been determined.Institute of Chemistry, Bashkir Branch, USSR Academy of Sciences, Ufa. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 439–443, May–June, 1988.     

Configuration and conformation of methyl 2,3-anhydro-4-deoxy-pyranosides by 1H and 13C NMR spectra

¹³C NMR spectra of 24 methyl 2,3-anhydro-4-deoxy-pento and hexopyranosides have been obtained. ¹H NMR spectra were also recorded for comparison purposes. The ¹³C NMR data can be used for differentiation of the stereo-isomeric epoxide configuration. ¹H and ¹³C NMR spectra give some insight, though still of qualitative nature, into conformation of epoxy compounds.     

15N and 31P NMR spectroscopy of triclorophosphazopolyfluoroaryls.

¹⁵N and ³¹P NMR spectra of trichlorophosphazopolyfluoroaryls obtained by the interaction between polyfluoroanilines and PCI₅ in benzene (Kirsanov reaction) have been investigated. The interconversions of monomeric and dimeric forms of trichlorophosphazopolyfluoroaryls by ³¹P NMR are also shown.     

Strukturaufklärung einer neuen diterpensäure aus metasequoia glyptostroboides mit hilfe der 13C-NMR-spektroskopie

In addition to methyl communate (1) the hitherto unknown 3-acetoxylabda-8(20), 13-diene-15-oic acid (3) has been isolated from the autumnal leaves of metasequoia glyptostroboides. Its structure has been determined by ¹³C NMR spectroscopy, aided by the analysis and assignment of the ¹³C NMR spectra of two degradation products as well as of α-onocerine diacetate (13) and of methyl communate (1).     

Solid-state high-resolution 29Si NMR in zunyite

High-resolution ²⁹Si NMR spectra of zunyite Si₅Al₁₃O₂₀ (OH,F)₁₈Cl have been studied by magic-angle sample spinning in combination with high-power proton decouplina and polarization transfer. The isotropic ²⁹Si chemical shift depends mainly on the number of Si-O-Si bridges and the bond angles in these bridges connecting the different SiO₄ tetrahedra.     

15N and 31P magnetic resonance spectra of P(N(CH3)2)3) in liquid crystal. Geometry and phosphorus chemical shift anisotropy

The ¹⁵N and ³¹P NMR spectra of the triply ¹⁵N labelled molecule P(N(CH₃)₂)₃ oriented in a nematic phase, is reported. The NPN bond angle is found equal to 97.6 ± 0.3 ° and the ³¹P chemical shift tensor anisotropy Δσ equal to 80 ± 15 ppm.     

13c-chemische verschiebungen und substituenteneffekte in methylazulenen

The ¹³C chemical shifts of all possible monomethyl azulenes and of some polymethyl derivatives have been determined by the Pulse Fourier Transform technique and have been assigned on the basis of ¹³C,H coupling constants and/or splitting patterns taken from proton coupled ¹³C NMR spectra. The shift differences observed in the monomethyl derivatives as compared to azulene itself are additive as far as sterically unperturbed polymethyl derivatives are concerned and can be viewed on as substituent constants. As is shown by the results of HMO- and EHT-calculations the substituent induced shifts in monomethyl azulenes without sterical hindrance can be correlated with charge density changes, with the exception of the β -effect, which is proportional to the bond length resp. the π bond order.     

17O NMR spectroscopy of transition metal carbonyls

NMR spectra of ¹⁷O in natural abundance have been obtained for a range of metal carbonyls. Linewidths of less than 10 Hz for the derivatives of Cr, Mo, W and Fe have been observed, although they are slightly larger for the derivatives of metals having an electric quadrupole moment. Comparison with the corresponding ¹³C NMR data shows that: (i) the chemical shift ranges are comparable, (ii) the ordering of chemical shifts is not very different, (iii) the linewidths are more favourable for ¹⁷O than ¹³C for some Mn and Co derivatives and allow an extension of the range of temperature in which information on the fluxional dynamics are obtainable in the rapid exchange limit.