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.     

13C NMR-spectroscopy of polymethoxyxanthones

The ¹³C NMR chemical shifts of eight methoxy-xanthones are reported. Methoxy substituent effects depending on substituent position as well as on shielded ring carbon position have been evaluated. Methoxy substituent increments for xanthones are proposed.     

Computer-assisted determination of carbon connectivity patterns based on natural abundance one-bond 13C13C coupling constants: terpenes

With the help of the interactive computer program CABSA the carbon connectivity pattern of representative known terpenes was established by measuring the one-bond ¹³C¹³C coupling constants in the presence of the signals of molecules containing one ¹³C isotope.     

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.     

Lithium dialkylamides. 13C parameters and slow proton transfer

The changes in ¹³C chemical shifts for the structural change R₂NH → R₂NLi have been measured for a series of dialkylamines. These lithiation shifts are largest at the $\text{alpha}$ carbon (3.7 – 9.7 ppm) and decrease in the order α > β > γ > δ. The rates of lithium-hydrogen interchange between R₂NH and R′₂NLi have been determined. The activation energies are large (9 – 17 kcal/mole) and increase as the size of R or R′ increases. The slow exchange permits the direct measurement of acidity differences between pairs of amines using ¹³C nmr.     

13C13C spin spin coupling constants in azulenes

[4-¹³C]- Azulene and [4-¹³C]-4-methylazulene have been synthesized. The ¹³C¹³C spin coupling constants have been measured and interpreted in terms of πMO theory.     

Biosynthese de la botryodiplodine,mycotoxine de penicillium roqueforti: Incorporations d'acetate[1-13C], [2-13C], [1-2 13C]et d'acide orsellinique 2-13C-carboxyle 13C], [3-4 13C]

Incorporations of [1-¹³C], [2-¹³C], [1-2¹³C]acetate and [2-¹³C, carboxyl-¹³C], [3-4¹³C]orsellinic acid into botryodiplodin indicate that this mycotoxin is biosynthesized by the polyketide pathway. Orsellinic acid is a precursor of botryodiplodin. A biosynthetic pathway, using orsellinic acid as precursor, is proposed.     

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 Hyperfine interaction in the hexafluorobenzene radical anion

Naturally abundant ¹³C satellites have been detected in the isotropic EPR spectrum of C₆F^?₆, the ¹³C coupling being 12.1 G The magnitude of this coupling does not support a nonplanar structure for C₆F^?₆. Also, the value is more consistent with a σ¹ than a π¹ configuration in D_6h, symmetry.     

Microwave spectra of tetrahydroselenophene-α13C, -β13C and molecular ring structure

Microwave spectra of isotopic species α-¹³C and β-¹³C of tetrahydroselenophene molecules have been investigated and rotational constants determined: A = 5608.98 Mc, B = 2819.532 Mc, C = 2022.624 Mc forα-¹³C isotopic species and A = 5695.94 Mc, B = 2770.714 Mc, C = 2009.166 Mc for β-¹³C isotopic species. The r_s-ring structure was found to be Se-C₂ = 1.963 Å, C₂-C₃ = 1.549 Å, C₃-C₄ = 1.527 Å, ∠C₅SeC₂ = 90° 44', ∠SeC₂C₃ = 104° 58', ∠C₂C₃C₄ = 106° 52', the angle of twist = 29° 44'.     

Vitamin C—A 13C magnetic resonance study

The pH dependence of the ¹³C chemical shifts of ascorbic acid has been measured and interpreted in terms of protonation sites. The transition of the dimer of dehydroascorbic acid into the hydrated monomer form is monitored by ¹³C spectroscopy.     

13C NMR spectroscopy of cyclopentenpoliols

The ¹³C NMR spectral parameters of eleven cyclopentenpoliols are discussed. Chemical shift criteria to distinguish isomeric 3' and 4' monodeoxy eucommiols have been clearly established.     

13C NMR spectra of some methylplatinum(IV) complexes

The ¹³C NMR spectra of some methylplatinum(IV) Schiff-base and related complexes have been recorded. The results are interpreted in terms of the differing effects of various donor atoms on a platinumcarbon bond in the trans position.     

Natural abundance 13C13C coupling constants observed via double quantum coherence. The two-dimensional ‘inadequate’ experiment for 13C NMR spectral analysis of erythronolide - B

A one- and a two-dimensional INADEQUATE NMR experiment afforded one-bond ¹³C¹³C coupling constants at natural abundance and total unambiguous signal assignment for erythronolide-B (1). ¹³C¹³C coupling constants at natural abundance and total unambiguous signal assignment for erythronolide-B (1).     

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     

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.     

13C NMR study of ethers complexed with nitroxide radical

The contact shifts of carbon nuclei in five ethers complexed with 2,2,6,6-tetramethylpiperidine nitroxide radical were determined from the ¹³C NMR spectra and explained by collision interactions.     

13C NMR study of ethers complexed with nitroxide radical

The contact shifts of carbon nuclei in 5 ethers complexed with 2,2,6,6-tetramethylpiperidine nitroxide radical were determined from the ¹³C NMR spectra and explained by collision interactions.     

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.     

13C NMR study of alcohols complexed with nitroxide radical

The contact shifts of carbon nuclei in 8 alcohols complexed with 2,2,6,6-tetramethylpiperidine nitroxide radical were determined from the ¹³C NMR spectra and explained by hydrogen bonding and collision interactions.