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.     

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).     

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.     

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 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.     

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'.     

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     

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.     

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.     

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 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.     

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.     

Use of13C/12C ratios for studying the origin of CO2 in sparkling wines

Summary ¹³C/¹²C ratios were measured in an attempt to determine the origin of the CO₂ in New Zealand commercial sparkling wines. This technique enabled a distinction to be made between CO₂ originating from C-3 plants, C-4 plants and that originating from an industrial source. With the additional measurement of the alcohol¹³C/¹²C ratios, it was possible to draw conclusions as to the wine making techniques used.

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Anwendung von¹³C/¹²C-Isotopenverhältnismessungen zur Bestimmung der CO₂-Herkunft in Handelssekt

Zusammenfassung Die Messung von¹³C/¹²C-Isotopenverhältnissen wurde dazu benutzt, um in neuseeländischem Handelssekt den Ursprung des CO₂ zu bestimmen. Mit dieser Methode konnte zwischen CO₂ aus C-3- und aus C-4-Pflanzenprodukten und CO₂ technischen Ursprungs unterschieden werden. Bei zusätzlichen¹³C/¹²C-Verhältnismessungen an Ethanol von Sektproben war es möglich, Rückschlüsse auf die Art der Sektherstellung zu ziehen.

     

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.     

Magnetic field dependent 13C and 1H CIDNP from biradicals. The role of the hyperfine coupling constant

Magnetic field dependent biradical CIDNP has been observed in the natural abundance ¹³C and ¹H NMR spectra taken immediately after irradiation of cyclic ketones in an auxiliary magnet. The ¹³C field dependence curves differ from the corresponding ¹H curves: The maxima of the curves for the C₁₁ and C₁₂ biradicals appear at a higher magnetic field strength, and the ¹³C curves are broader than the ¹H curves. These differences are due to the different magnitudes of the hyperfine coupling constants for ¹³C and ¹H and can be accounted for by a model based on a stochastic Liouville method which incorporates the dynamics of the biradicals.     

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.     

NMR study (1H, 13C and 29Si) of the methylallylsilanes

¹H, ¹³C and ²⁹Si NMR data for the compounds (CH₃)_xSi(CH₂CHCH₂)_4-x are reported. The ¹H resonances from the π system are indicative of the electron-supplying inductive effect (+I) of the (CH₃SiCH₂, moiety but the corresponding ¹³C_π chemical shifts seem to be influenced by a sterically induced polarization of the C-H bonds. The ¹³C_All, ¹³C_Me and ²⁹Si chemical shift data reveal an important neighbour anisotropy contribution originating from the π system. Ultraviolet study of the compounds mentioned above gives indication of a σ—π conjugation in accordance with PES and ab initio results [1—5]. The trend observed in the various coupling constants is too small to be Interpreted.     

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.     

Synthesis and nmr analysis of cyclo-[85% 13C-asp]-pro: 13C-13C vicinal coupling constants and conformation

The dipeptide cyclo(Asp-Pro) where the aspartic acid residue was 85% ¹³C enriched, was synthesized with the aim of analyzing its conformation in solution by using ¹C-¹H, ¹³H-¹H and ¹³C-¹³C coupling constant parameters. The values of these couplings agree well with each other and show that the side chain of the aspartic acid residue adopts privileged conformations the proportions of which vary somewhat with pH, and more weakly, with a change in solvent. The ¹³C-¹³C interresidue coupling constants ³J_Cl'–_C2^β and ³J_Cl'–_C2^γ obtained after long accumulation of the signals of unenriched carbons, have different values; they show puckering in the pyrrolidine ring similar to that found in cyclo(Leu-Pro) in the solid state. It was concluded that ¹³C-¹³C coupling constants represent an excellent means of determining the side chain conformation (whenever the incorporation of an enriched amino acid into the peptide is possible) that will find applications particularly in the case of peptides with complicated proton spectra.