Quantitative analysis by nuclear magnetic resonance with fourier transform II?13C resonance

Quantitative analyses have been carried out by ¹³C NMR spectroscopy using Fourier transformation. The Overhauser effect, due to the broad band decoupling of protons, has been suppressed using the two existing methods (gated decoupling and paramagnetic species), and results from each are compared. Both require a calibration curve, and the second method, when applied to aromatic substances, needs the ratio between the sample to be analysed and the paramagnetic species to be less than a certain value. Experiments have been made with pure products and blends of pure products containing both saturated and aromatic carbons. The precision of the results is given.     

1H and 13C NMR spectral analysis of some necines of toxic pyrrolizidine alkaloids

Summary The total assignment of the ¹H and ¹³C NMR spectra of the necines of toxic pyrrolizidine alkaloids (retronecine, heliotridine, crotanecine, otonecine), their hydrochlorides and their N-oxides has been performed. The characteristic chemical shift differences between retronecine and heliotridine, as well as the protonation and N-oxidation shift effects in NMR studies of necines at the corresponding position are proposed to be an additional assignment aid. The assignment of the spectra was achieved by the concerted use of 2D correlation spectroscopy.Dedicated to Prof. Dr. Dr. Dres. h. c. Herbert Oelschläger, Frankfurt/Main, on the occasion of his 70th birthday     

Inductive substituent constants σji from olefinic geminal 1h, 1h nmr coupling constants

Theoretical and experimental arguments are presented supporting the postulate that olefinic NMR coupling constants ²J_HH are insensitive to β-substituent influences on the olefinic π orbital. A new set of substituent constants, σ^J_I, is proposed to measure directly the inductive substituent effect transmitted by σ-bonds. The previously available range of inductive substituent constants can be appreciably extended in this way. Comparisons of σ^J_I with other observables and parameters for selected substituents are made as a test of consistency.     

13C nuclear magnetic resonance spectra of aflatoxin B1 derived from acetate

The labeling distribution of the fungal metabolite, aflatoxin B₁, produced from [1- or 2- ¹³C] acetate was determined by ¹³C FT NMR. The results support the polyketide hypothesis for aflatoxin biogenesis.     

The 1H and 13C nuclear magnetic resonance and IR adsorption spectra of substituted polymethylferrocenes

The NMR and IR spectra of sym-polymethylferrocenes have been studied. The abnormal shifts observed of the ¹³C signals from the adjacent methyl groups are discussed in terms of spatial interactions between these groups, which cause charge redistribution in the vicinity of the ¹³C nuclei.     

Quantitative analysis by nuclear magnetic resonance with fourier transformation: I—Proton case

For quantitative analysis by NMR spectroscopy with Fourier transform, the usual experimental conditions have to be partly modified. Careful regulation of the delays between the different phases of the process is particularly important. The filters of the spectrometer and the calculations on the free induction decay are important causes of error. Precise results are given.     

13C nuclear magnetic resonance spectroscopy of atisine and veatchine-type C20-diterpenoid alkaloids from aconitum and garrya species

¹³C NMR spectra of the atisine- and veatchine-type alkaloids, as well as certain of their derivatives, have been obtained by the Fourier transform technique at 25.03 MHz. With the help of single-frequency off-resonance proton decoupling techniques, additivity relationships, and the effects induced by certain structural changes, self-consistent assignments of nearly all the resonances have been made. The ¹³C NMR spectra are also analyzed to identify skeletal features of the atisine and veatchine-type alkaloids of use in the structure determination of new C₂₀-diterpenoid alkaloids. On the basis of the ¹³C NMR analysis of atisine and veatchine as well as a temperature-dependence study of atisine, the existence of C-20 epimers in these alkaloids is demonstrated. A ¹³C NMR study of the behavior of the oxazolidine ring of atisine in non-ionic and ionic solvents indicates that the C-20 epimers of atisine do not exist in an equilibrium mixture in solution and are not interconvertible via a zwitterion as reported earlier.     

129Xe nuclear magnetic resonance studies of supported platinum-alumina catalysts

¹²⁹Xe nuclear magnetic resonance spectra of xenon adsorbed on supported platinum-alumina catalysts have been examined. The state of metallic platinum particles (Pt^o) was shown to be different for Pt/Al₂O₃ and Pt/Al₂O₃(Cl) samples. Some assumptions about the mutual arrangement of supported metallic particles have been made.

---

¹²⁹Xe , , Pt⁰ Pt(II). , (Pt⁰) , . Pt⁰ Pt(II).

     

13C nuclear magnetic resonance spectra of ethers and glycols

The ¹³C NMR spectra of 21 linear and branched ethers together with the corresponding alcohols have been determined in an attempt to correlate the shieldings in both series. It has been found that the shielding of a carbon in an acyclic ether can be given by the summation of additive shift parameters for substituents and correction parameters for the substitution patterns based on the shielding of the parent alcohol. On examination of solvent-induced shifts for α- and β-carbons in ethers and alcohols, significant ones have been noted in carbon tetrachloride→dimethylsulfoxide and carbon tetrachloride→trifluoroacetic acid. No appreciable concentration-dependent shifts of the shieldings have been observed in both ethers and alcohols. For the shieldings of α-carbons in acyclic glycols, it has been noticed that the observed and predicted values are in accord in 1,3-, 1,4- and 1,5-glycols but deviate in 1,2-glycols. The latter has been examined in a polycyclic system, where the deviations ( > 3·5ppm) in a cis (gauche) 1,2-glycol are larger than those (<2·5 ppm) in a trans (anti-parallel) 1,2-glycol.     

129Xe nuclear magnetic resonance in the clathrate hydrate of xenon

The sensitivity of the nuclear magnetic shielding of the Xe atom to the physical environment makes it possible to “see” well-separated. ¹²⁹Xe resonances from Xe atoms in the small and large clathrate deuteriohydrate cages as well as in the gas with which the hydrate is in equilibrium. The relative occupancy of the small cages is suostantially less than predicted oy existing models of guest-host interactions in Xe gas hydrate.     

A 13C nuclear magnetic resonance study of cyclobutadieneirontricarbonyl-substituted carbonium ions

The ¹³C NMR spectra of (hydroxymethyl)-, (α-hydroxyethyl)- and (α-hydroxybenzyl)cyclobutadieneiron tricarbonyl (in CDCl₃) and of their derived carbonium ions (in concentrated H₂SO₄) are reported. The data suggest extensive donation of electron density from the metal, via the cyclobutadiene unit, to the exocyclic, electron-deficient carbon atom, thus giving highly stabilized carbonium ions.     

Studies on the structure of olivomycin a and mithramycin by 1H and 13C nuclear magnetic resonance spectroscopy

Extensive ¹H and ¹³CNMR studies confirmed the gross structure of olivomycin A except for a revision with respect to a saccharide linkage. The structure of mithramycin was elucidated similarly, resulting in a substantial revision of structure for its carbohydrate moiety including interglycosidic bonds.     

Rotational isomerism. A gas-phase 1H nuclear magnetic resonance study of 1-bromo-2-chloroethane

The average vicinal coupling constants of 1-bromo-2-chloroethane at different temperatures have been obtained in a gas-phase ¹H NMR study of 1,2-disubstituted ethanes. Analysis of the experimental data, assuming a ”static” model with constant values for the vicinal coupling constants of the individual rotamers, yielded unacceptable results. A ”dynamic” model, which takes into account the torsional vibrations, has therefore been developed and used to analyse the gas-phase results. The values at 305 K for the vicinal coupling constants of the individual rotamers are: trans rotamer J_T = 13.6 Hz, J'_t = 4.9 Hz; gauche rotamer $\text{1}\text{2}$(J_G1 + J_G2) = 0.9 Hz, $\text{1}\text{2}$(J'_G1 + J'_G2) = 7.8 Hz. These couplings are temperature-dependent with J_T changing about four times as much as the other coupling constants. Analysis of the average vicinal coupling constants, measured in different solvents, with the “dynamic” model gave values for the vicinal coupling constants of the individual rotamers in excellent agreement with those from the gas-phase data. The value of $\text{1}\text{2}$(J_G1+ J_G2) decreases noticeably with increasing dielectric constant of the solution. This can be explained by changes in the average dihedral angle between the coupling protons, in the gauche rotamers, which leads to changes of J_G1 and J_G2 in the same direction.     

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.     

The conformation of succinic acid in aqueous solution studied by 1h and 13c nmr

The vicinal H-H coupling constants of succinic acid were obtained as a function of pH and related to its conformation. The syn-clinal arrangement of the two CO₂H groups appears as more stable than the anti-periplanar conformation at variance with previous work but in agreement with recent data on similar molecules. The vicinal¹³CO₂H-¹H coupling constant was also obtained and is found to support that conclusion. The analysis was extended to solvents of variable dielectric constant and no significant effect was found.     

The analysis of dinitrotoluene isomer mixtures by nuclear magnetic resonance

NMR data are given for all the dinitrotoluene isomers. It is shown that the components in mixtures of these isomers produced for example, by the direct nitration of toluene, can be recognised readily by NMR. Quantitative analyses can be performed using the heights of the methyl proton peaks of the various isomers. The accuracy of the method and the effects of any residual toluene or mononitrotoluenes are discussed.