13C-NMR spectra and carbon-proton coupling constants of variously annulated furocoumarins

The ¹³C-nmr spectra of variously annulated methylfurocoumarins are reported. The assignments of chemical shifts for all the C resonances has been achieved by using carbon-proton coupling constants, relaxation efficiency considerations and shift effects caused by the introduction of methyl groups at various positions of the furocoumarin nucleus. Substituent effects on ¹³C chemical shifts and carbon-proton coupling constants are discussed.     

13C n.m.r. spectra of 2-substituted pyrimidines

¹³C n.m.r. chemical shifts and carbon-proton coupling constants of 2-substituted pyrimidines are reported. The carbon chemical shifts are correlated with π-electron densities. Substituents which cause deshielding at the directly bound carbon (e.g. NH₂, OCH₃ and F) exert a more powerful effect in the benzene series than in the pyridine or pyrimidine series. The carbon-proton coupling constants do not correlate with the electronegativity of the substituents. Carbon-proton coupling constants and proton-proton coupling constants over the same number of bonds do not obey the Karabatsos relationship. The changes in the carbon-proton coupling constants in 2(1H)-pyrimidinone and 2(1H)-pyrimidinethione which accompany anion and cation formation are reported.     

13C NMR spectra of benzothiazepinone,benzothiazinone and benzosulphonamide N-substituted derivatives

A comparative study of the ¹³C NMR spectra of benzothiazinone and benzothiazepinone dioxide derivatives and of some structurally related benzosulphonamides is presented. The size of the heterocyclic ring is reflected in the ¹³C chemical shifts and in the one-bond carbon-proton aromatic coupling constants. An upfield γ-effect of sulphur on the ¹³C chemical shifts in N-substituted carboxyethylbenzene-4,5-dimethoxysulphonamides is reported.     

Furopyridines. XI. 13C NMR Spectra of 2- or 3-Substituted Furo[2,3-b]-, Furo[3,2-b]-, Furo[2,3-c]- and Furo[3,2-c]pyridine

The ¹³C nmr spectra of 2- or 3-monosubstituted furo[2,3-b]- 1a-1j , furo[3,2-b]- 2a-2j , furo[2,3-c]- 3a-3j and furo[3,2-c]pyridine derivatives 4a-4j are reported. Effects by change in annelation and substituent effects on ¹³C chemical shifts and carbon-proton coupling constants are discussed. The spectra of benzo[b]furan derivatives 5a-5j having the corresponding substituent are also reported for comparison.     

13C NMR spectra of alkyl- and phenylpyrazines and their N-oxides

The ¹³C chemical shifts of 37 pyrazines, including their N-oxides, are reported. Substituent effects of methyl, phenyl and N-oxide groups on the chemical shifts were examined. To comprehend these effects, the chemical shifts were compared with charge densities calculated by the CNDO/2 method and a good correlation was obtained. ¹³C, ¹H coupling constants of some pyrazines were also determined and assigned. These data enable us to assign the ¹³C NMR spectra of substituted pyrazines and to understand the effects of N-oxidation on the pyrazine nuclei.     

13C?19F spin–spin coupling in some monofluoro-substituted polycyclic aromatic hydrocarbons

The determination and complete assignment of the ¹³C? ¹⁹F coupling constants and ¹³C chemical shifts for 15 monofluoro derivatives of nine polycyclic aromatic hydrocarbons are reported. Fluorine substitutent effects on the ¹³C chemical shifts are given and their regular behaviour, making comparisons between different compounds possible, is discussed. The numerical values of the ¹³C? ¹⁹F long range coupling constants are found, with a few exceptions, to decrease in an alternating manner along the periphery of the molecules. In several cases the signs of the coupling constants have been determined. It appears that the signs alternate, but additional evidence is required. The magnitudes of different types of coupling constants are discussed in terms of steric and electronic effects. CNDO/2 and INDO calculations of the ¹³C? ¹⁹F coupling constants in the fluoronaphthalenes have been performed using the ‘sum-over-states’ method with the aim of examining the orbital and spin–dipole contributions to the various couplings.     

13C NMR spectra and three-dimensional structures of isomeric 3,4-substituted thiophans

The chemical shifts and the direct carbon-proton spin-spin coupling constants for a number of cis and trans isomers of 4-amino-substituted 3-hydroxy(acyloxy)-thiophans, the configurations of the substituents in which and the conformational states were previously established by an independent method, were studied. It was found that in the spectra of the cis isomers the signals of the vicinal ¹³C atoms, which bear the substituents, are shifted to strong field as compared with the trans isomers ( trans-cis 1.7–4.3 ppm). Conformational effects of the substituents on the chemical shifts of the ring ¹³C atoms were noted. It is shown that a relationship exists between the direct carbon-proton spin-spin coupling constants and the spatial orientations of the acyloxy and acylamino substituents for five-membered saturated rings.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1612–1616, December, 1981.     

Carbon-13 NMR spectroscopy of heterocyclic compounds—IV : A 20 MHz study of chemical shifts and carbon-proton coupling constants in a series of hydroxy,methoxy and glucosyl coumarins

Complete assignments of chemical shifts and extensive assignments of carbon-proton coupling constants are presented for all the monohydroxycoumarins except the 5-derivative, together with similar data for 6,7- and 7,8-dihydroxy-,4- and 7-methoxy-, 7-hydroxy-4-methyl- and 6,7- and 7,8-dihydroxy-4-methyl-coumarins. It is shown that shifts in the polysubstituted molecules can be predicted with high precision from substituent effects evaluated for the more simple derivatives. The approach is extended to some simple glucosyl derivatives, and it is demonstrated that not only the anomeric configuration but also the exact site of the sugar substitution can be determined from ¹³C data.     

Stereospecificity of <Superscript>13</Superscript>C shielding constants in acetone azine as a tool for configurational assignment of ketone azines

According to the ¹³C NMR data, the chemical shift of the methyl carbon atom in acetone azine in the trans position with respect to the lone electron pair on the neighboring nitrogen atom is lower by 7 ppm than that of the methyl carbon atom in the cis position. The corresponding direct ¹³C-¹³C coupling constant for the trans-methyl groups is lower by 10 Hz as compared to the cis-methyl groups. The experimental spectral data are reproduced well by nonempirical quantum-chemical calculations. The observed stereospecificity of ¹³C chemical shifts and ¹³C-¹³C coupling constants may be used as an effective tool in configurational analysis of various ketone azines.     

Carbon Magnetic Resonance Spectra of α, β, γ, δ- and α, β, α′, β′- Unsaturated Ketones

Carbon-13 spectra of a series of 26 unsaturated ketones (ortho- and para-cyclo-hexadienones and corresponding open-chain analogues) have been measured by Fourier-transform. Pulse spectroscopy. A complete analysis has been achieved by means of double resonance experiments using noise-modulated and coherent off-resonance proton irradiation and with the aid of non-decoupled spectra. Chemical shifts are interpreted in terms of charge distribution in the dienone system and of methyl substituent effects. Carbon chemical shifts were also obtained for O-protonated ortho- and para-cyclohexadienones. One-bond and long-range carbon-proton and carbon-fluorine spin coupling constants are reported for several compounds.     

Carbon-13 NMR spectra of some 4- and 5-substituted pyrimidines

Carbon-13 NMR chemical shifts and carbon-proton coupling constants for nine 4-substituted and six 5-substituted pyrimidines are reported. The carbon chemical shifts are correlated with π-electron densities. Carbon-proton coupling constants fail to correlate with substituent electronegativity.     

13C n.m.r. spectra of cyclopropenes

¹³C n.m.r. chemical shifts and one bond ¹³C, ¹H coupling constants for cyclopropene and its 1- and 3-methyl derivatives as well as for methyl cyclopropane have been measured. The data for cyclopropene are 108·9 ppm and 228·2 Hz, 2·3 ppm and 167·0 Hz in the olefinic and allylic position, respectively. Substituent effects for the methyl group are discussed.     

Hochauflösungs-13C-NMR-Spektroskopie. I—Analyse der Spektren des 1,2,4- und 1,3,5-Triazins sowie ihrer Methyl- und Phenylderivate

Using the pulse Fourier transform technique, the high resolution carbon-13 NMR spectra of 1,2,4- and 1,3,5-triazine and their methyl derivatives as well as the ¹H noise decoupled spectra of phenyl- and methylphenyl substituted triazines, have been recorded and analysed. The chemical shifts of the polysubstituted 1,2,4-triazines normally show additivity; deviations observed with phenyl derivatives are ascribed to steric effects. The ¹³C? H coupling constants are compared to those of benzene, pyridine, the diazines and disubstituted ethylenes. The strong influence on the coupling constants exerted by number and position of the nitrogen atoms is revealed by the observation that geminal couplings in 1,2,4-triazine are larger than vicinal ones, in contrast to the usual sequence.     

1H and 13C NMR studies of 7-azaindole and related compounds

The ¹H and ¹³C chemical shifts, proton-proton coupling constants, and one-bond carbon-hydrogen coupling constants have been obtained for 7-azaindole, 1-methyl-7-azaindole, their corresponding methyl iodide salts, and the related compound 7-methyl-7H-pyrrolo [2,3-b]pyridine. are different from those of either 7-azaindole or 1-methyl-7-azaindole.     

13C and proton NMR spectra of 2(1H)pyrazinones

¹³C and proton NMR spectra data are given for eleven 2(1H)pyraziones. Assignments of chemical shifts were made by methods which included: deuterium exchange with certain protons of 3-alkyl substituents; change of chemical shifts of certain carbon atoms with change in pH; the use of long-range coupling constants for ¹³C to protons; and various correlations among assigned spectra.     

Chemistry of the phenoxathiins and isosterically related heterocycles. IX.N-oxidation on the 13C-nmr chemical shifts and coupling constants of the 1-azaphenoxathiin system

The synthesis of 1-azaphenoxathiin N-oxide is described. Total assignment of the ¹³C-nmr spectrum and the effects of the N-oxide moiety on the chemical shifts and ¹H-¹³C spin couplings constants are described and compared to the parent 1-azaphenoxathiin system. The potential for the use of N-oxidation induced changes in ¹³C-nmr chemical shifts and ¹H-¹³C coupling constants as an assignment criterion is also discussed.     

1H and13C NMR spectra and structure of 2,3,4-trisubstituted sulfolanes

Conclusions The¹H and¹³C NMR spectra were studied for 2,3,4-trisubstituted sulfolanes and the isomerism of these compounds was determined, The use of chemical shift information is more convenient to determine the isomerism of polysubstituted cyclic compounds by PMR spectroscopy, while use of the direct carbon-proton coupling constants is more convenient for this problem when employing¹³C NMR spectroscopy.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2498–2501, November 1984.     

13C NMR spectra of some 1-, 3- and 4-monosubstituted and disubstituted isoquinolines

Chemical shifts and substituent chemical shift (SCS) effects are reported for 21 monosubstituted iso-quinolines, carrying a halogeno, amino, piperidino or ethoxy group in position 1, 3 or 4. In some cases, assignments of ¹³C resonances were based on the spectra of the corresponding 5-deutero derivatives. For the fluoroisoquinolines some ¹³CF coupling constants are given. The ¹³C NMR spectra of 15 disubstituted isoquinolines were measured; with a few exceptions, mainly the 3,4- and 1,4-disubstituted isoquinolines, the chemical shifts agreed well with those calculated by addition of the SCS effects.     

Etudes des sélénophènes mono et bisubstitués par Résonance Magnétique de 1H et de 13C

Proton and carbon magnetic resonance spectra of mono-and disubstituted selenophenes are investigated. The proton chemical shifts are discussed in terms of magnetic anisotropy and electric field effects of the substituents, with a view to studying the conformational equilibrium of the carbonyl group. π Electronic charges, computed by the PPP method, are correlated with the proton and carbon chemical shifts. The coupling constants between ¹³C and ¹H (1, 2 or 3 bonds) and ¹³C? ⁷⁷Se are shown to be good structural parameters and a set of substituent additivity constants is calculated.     

Trimethylsilylation - Aid in NMR Analysis of Oligosaccharides. Assigment of 29Si and 13C NMR Spectra of Trimethylsilylated Methyl β-D-Xylobiosides by 2D NMR

The ¹H, ¹³C and ²⁹Si NMR spectra of methyl β-D-xylopyranoside and three methyl β-D-xylopyranosyl-β-D-xylopyranosides have been measured and assigned by two-dimensional NMR spectroscopy. According to the determined proton-proton coupling constants, the ring conformer ratio is essential ly the same in the studied compounds. The assigned chemical shifts provide correct substituent chemical shifts for assignments in the spectra of higher trimethylsilylated xylooligosaccharides. Heteronuclear chemical shift correlated 2D NMR spectroscopy is proven to be a usable experimental method for ²⁹Si NMR line assignment in carbohydrates. The assigned silicon shifts identify the site of glycosidation.