13C NMR of pterocarpans

¹³CNMR spectra of eight pterocarpans are reported Assignments are based on multiplicities and second-order features in off-resonance decoupled spectra and on chemical shifts in model compounds. Comparison of the degree of long-range (C, H) coupling in ¹H-coupled spectra is found useful     

13C NMR spectrum of coumarin

Summary The positions of the signals from the C₃, C₅, C₆, and C₇ carbon atoms in the¹³C NMR spectrum of coumarin have been established with the aid of information obtained from the¹³C NMR spectra of [3-D]-, [4-D]-, and 7-methoxycoumarins and by the use of an additive calculation based on the increments of the methoxy group in the¹³C NMR spectrum of anisole.M. V. Lomonosov Moscow State University Scientific-Research Institute of Pharmacology, Academy of Medical Sciences of the USSR. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 458–462, July–August, 1975.     

Fourier 13C NMR and PMR including 13C satellites of oriented cyanopropyne

Fourier ¹³C and proton NMR spectra of cyanopropyne partially oriented by a nematic phase have been recorded and interpreted. It is shown that more accurate measurements are obtained much more rapidly by observing ¹³C satellites by Fourier PMR than by direct observation of the ¹³C spectrum. The geometry has been extracted from direct couplings; a small but systematic discrepancy with microwave spectroscopy is observed for the carboncarbon bond lengths.     

13C NMR spectroscopy in diamonds using dynamic nuclear polarization

In diamonds unpaired electrons associated with nitrogen impurities can be used to enhance the ¹³C NMR signal via the solid-state effect. ¹³C spectra of three natural and two synthetic diamonds are shown that were obtained in this manner in 10–30 min.     

Structural analysis of alkylated coal by 1H and 13C NMR spectroscopy

Summary A method is presented for derivation of a series of structural parameters describing the average molecule of soluble butylated coal. It is based on ¹H and ¹³C NMR spectral data, molecular mass measurement and ultimate analysis. Average structural models of coals can be constructed in this way.

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Strukturanalyse von alkylierter Kohle mit Hilfe der ¹H- und ¹³C-NMR-Spektroskopie

Zusammenfassung Ein Verfahren wird vorgestellt zur Ableitung einer Reihe von Strukturparametern, die das Durchschnittsmolekül von löslicher butylierter Kohle beschreiben können. Es beruht auf ¹H- und ¹³C-NMR-Spektraldaten, Messungen der Molekülmasse sowie der Elementaranalyse. Durchschnittliche Strukturmodelle von Kohlen können dadurch erstellt werden.

     

Chiral relaxation reagents (CRR) in 13C NMR spectroscopy

Enantiomers and chiral relaxation reagents (CRR) afford diastereomeric complexes, which differ clearly in their ¹³C spin-lattice relaxation times.     

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.     

29Si and 13C NMR spectra of permethylpolysilanes

²⁹Si, ¹³C and ¹H NMR spectra are reported for the series of linear permethylpolysilanes Me(SiMe₂)_nMe where n = 1 to 6, for the cyclic permethylpolysilanes (Me₂Si)_n where n = 5 to 8, and for a few related compounds. For linear polysilanes the ²⁹Si and ¹³C chemical shifts can be accurately calculated from simple additivity relationships based on the number of silicon atoms in α, β, γ and δ positions. Adjacent (α) silicon atoms lead to upfield shifts in the ²⁹Si and ¹³C resonances, whereas more remote silicon atoms lead to downfield shifts. The ²⁹Si chemical shifts of the polysilane chains are linearly related to the ¹³C shifts of the carbon atoms attached to the silicon. The ²⁹Si and ¹³C resonances of the cyclic silanes deviate from this relationship. Ring current effects arising from σ delocalization are suggested as an explanation for the deviations. Proton-coupled ²⁹Si NMR spectra are reported for Me₃SiSiMe₃ and for (Me₂Si)_n, n = 5 to 7.     

13C NMR spectroscopy of head-to-head polystyrene: Molecular motion in solution

Head-to-head polystyrene was studied by NMR relaxation measurements in solution and these measurements were compared with those for head-to-tail polystyrene. By measuring the relaxation of the ortho and meta carbons of the phenyl rings of the polystyrenes, it was found that the head-to-head polystyrene chain is stiffer (T_m = 65°) than the head-to-tail chain (T_m = 54°). These results are in agreement with the measurements of the radius of gyration, and results from the study of the melt rheology of head-to-head and head-to-tail polystyrene.     

13C high-resolution NMR study of undoped polyacetylene

¹³C NMR spectra of undoped polyacetylene,(CH)_x, have been measured. The existence of 3.4 mol% methylene moieties as defects in the (CH)_x chains has been observed in trans-(CH)_x. Measurements of partially cis-to-trans isomerized (CH)_x suggest the existence of isolated cis regions.     

13C NMR spectroscopy of naturally occurring iridoid glucosides and their acylated derivatives

The ¹³C NMR spectra of twenty one iridoid glucosides and fourteen acyl iridoid glucosides of various cyclopentane oxidation states have been analysed and their carbon shifts assigned. Evidence is presented which demonstrates that ¹³C NMR spectroscopy is a valuable and reliable technique for distinguishing the sites of acylation in iridoid glucosides and confirming the predictions of the configuration at C-6 and C-8. A cis configuration of vicinal substituents is generally associated with a substantial increase in shielding, as compared with the trans analog. The ring size and C-1 configuration in the glucose moiety are also evident from the spectra.     

13C NMR substituent effects in tetracyclic diterpenoids

The ¹³C NMR chemical shifts of ent-beyer-15-ene, and one hydroxy and four acetoxy derivatives are reported. The substituent effects of the acetoxy groups upon the saturated and olefinic carbon atoms are discussed. Conformational aspects of the molecules are considered in the light of these effects.     

Investigation of sesquiterpene lactones by13C NMR spectroscopy. III.13C MNR spectra of artemin and its derivatives

The¹³C NMR spectra obtained under conditions of complete and incomplete decoupling from protons of the sesquiterpene lactone artemin (I), its dihydro derivative (II), and its acetyl derivative (III) have been studied. An assignment has been made of the chemical shifts of all the carbon atoms by comparison of the¹³C NMR spectra of (I), (II), and (III) with one another and also by comparison with literature information.V. L. Komarov Institute of Botany, Academy of Sciences of the AzSSR, Baku, Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 576–578, September–October, 1983.     

14N and 13C NMR of tautomeric systems of hydroxy-pyridines

¹⁴N NMR is shown to be an efficient method of investigation of the tautomeric equilibria in hydroxy-and related substituted pyridines. Large relative ¹⁴N chemical shifts within tautomeric pairs estimated from N-Me and O-Me derivatives make possible quantitative determinations of the equilibria. Qualitative conclusions may be drawn from ¹⁴N line widths as well as from ¹³C and proton chemical shifts.     

NMR 13C study of the structure of polyethyleneimine

The NMR ¹³C (CMR) spectrum of high molecular weight (M = 20,000) branched polyethyleneimine (PEI) obtained by polymerization of ethyleneimine (EI) in aqueous and alcoholic solutions at 50° with 1,3-dichloropropanol as initiator, contains 8 lines. The lines were identified using CMR spectra of model compounds, i.e. linear PEI, regularly branched PEI, diethylenetriamine and ethyleneimine pentamer. It has been shown that the deshielding effect of the nitrogen atoms on the α-atoms of carbon decreases in the folowing order: N_tert > N_sec > N_prim; with the atoms of carbon in the β-position, the effect increases in the opposite order.A quantitative estimation has been made of the distribution of the diads of elementary units containing the same and different nitrogen atoms. The data have been used to draw some conclusions about the structure of the PEI macromolecule.