Sur la Similitude des Déformations du Noyau Cyclohexanonique Induites par les Groupes Tertiobutyle et gem-Diméthyle

X-ray and NMR (250 MHz) data for chlorinated 4,4-dimethylcyclohexanones lead to the following conclusions: carbonyl and chlorine substituent effects on ²J and ³J coupling constants are similar to those observed for 4-tert-butylcyclohexanones. In other respects, the gem dimethyl and the tert-butyl groups induce on the ring similar large ⁴J coupling constants (H-3′? C-3? C-4? C-5? H-5′); the results can be interpreted in terms of local gemoetric deformations and additivity of these deformations. The determination of dihedral angles by Lambert's method and from X-ray data shows the identity of the structures in the solid state and the dissolved state and confirms the great structural similarity between 4-tert-butyl- and 4,4-dimethylcyclohexanone derivatives.     

13C NMR spectra of 1-(α-aroyloxyarylideneamino)-1,2,3-triazoles. Identification of 4,5-unsymmetrically substituted derivatives

The ¹³C nmr spectra of the title compounds are reported. Chemical shifts of C-4 and C-5 carbons of the triazole ring are used for structural assignment of the 4,5-unsymmetrically substituted 1-(α-aroyloxyarylideneamino)-v-triazoles (triazolylisoimides). A complete assignment of the shifts of the α-aroyloxyarylideneamino group is given. Some J_C-H values are also reported.     

13C-NMR-Untersuchungen zur Strukturaufklärung von Polysacchariden und deren Methylderivaten

The ¹³C NMR spectra of some polysaccharides and their methyl derivatives have been analysed. The numbers and positions of the assigned ¹³C NMR signals give some information about the structure of the monomer unit and the positions of the glycosidic linkage but no information about the anomeric configuration. In this case the ¹J(C-1, H) coupling constants make it possible to identify the anomeric configuration, because the mean differences of the J values for the α- and β-anomers are 12 Hz (at least 5 Hz) with the higher values for the α-anomers.     

Preparation and reactions of 3,4-dihydro-2H-pyran-2-ones

The Michael reaction of ethyl cinnamates with deoxybenzoin gave ethyl 3,4,5-triaryl-5-oxopentanoates which were hydrolysed to the corresponding acids. The latter could be cyclized to the respective 3,4-dihydro-2H-pyran-2-ones which underwent ring opening with several nucleophiles to the corresponding acid derivatives. However, their reaction with ammonium acetate led to the formation of 3,4-dihydro-2-pyridones. The 3,4-dihydro-2-pyrones and pyridones were dehydrogenated to the corresponding 2-pyrones and 2-pyridones by fusion with sulfur.     

13C n.m.r. spectra of some pyrylium salts and related compounds

The ¹³C chemical shifts of several alkyl and phenyl substituted pyrylium perchlorates, together with related pyridine and pyridinium salts, are reported. The shifts in the isoelectronic series benzene, pyridine, pyrylium cation correlate well with charge densities calculated by INDO MO theory. Charge densities also account for the shift changes found at C-3, C-4 and C-5 for protonation of pyridine and 2,4,6-trimethylpyridine. The shift changes observed on protonation for C-2 and C-6, along the series pyridine, 2,4,6-trimethylpyridine and 2,4,6-triphenylpyridine can only be rationalized by consideration of both charge density and π-bond order changes. The effects of alkyl substitution on the shifts of the pyrylium cations are not accounted for by charge density changes. Empirical correlations of these shifts with literature data for the alkylbenzenes and the shifts of the phenyl substituted 6-membered heterocycles are discussed.     

An NMR study of 2-alkoxy-1,3,2-dioxaphospholanes. I—13C chemical shifts

Measurements of the ¹³C chemical shifts of 2-alkoxy-1,3,2-dioxaphospholanes have allowed the determination of the contribution of the substituent to the α-, β- and γ-carbon chemical shifts of attached alkyl groups. The preliminary assignments of the signals were made using the following information; relative intensities, variations in coupling constants J(³¹P¹³C) and the existence of linear correlations between the shifts of carbon atoms in the P-alkoxy groups and the degree of substitution of the observed carbon or of its neighbours.     

Conformational studies on pyranoid sugar derivatives by NMR spectroscopy. Correlations of observed proton—proton coupling constants with the generalized Karplus equation

Proton spin-spin coupling values measured for a wide range of tetrasubstituted tetrahydropyran ring-systems obtained from aldopentopyranose sugars have been correlated with values calculated from a generalized version of the Karplus equation which takes into account the electronegativities of the various atoms in the molecule and the configurations of these substituents. Minor discrepancies between observed and calculated values can be attributed to slight flattening of the tetrahydropyran ring as a result of steric interactions of the substituents. The magnitude of the geminal coupling J_5e,5a of these aldopentopyranose derivatives provides a rough measure of the conformational population; when H-4 is axial [Cl(D) or 1C(L ) conformation] J_5e,5a is ～10.9 Hz, and is ～13.4 Hz when H-4 is equatorial [1C(D ) or Cl(L ) conformation].     

Détermination par RMN 1H et 13C des Couplages J(CH) et J(CC) dans des Monomères Precurseurs de Lignine: Vanilline,Férulate d'Ethyle et Alcool Coniférylique Sélectivement Enrichis en 2H et 13C

Some monomer model compounds of lignin have been selectively ²H and ¹³C labelled: vanillin, ethyl ferulate, coniferyl alcohol and ethyl hydrogen malonate. Deuterium isotope effects on the ¹³C chemical shifts in [formyl-²H]vanillin, [5-²H]vanillin and [α,α,5-²H₃]coniferyl alcohol made the unambiguous assignment of the aromatic ¹³C signals possible. Absolute ^1,2,3J(CC) values have been determined on ¹³C spectra of [formyl-¹³C]vanillin, and of ethyl ferulate and coniferyl alcohol in which the vinylic C-γ and C-β carbons were ¹³C enriched. It has been possible to measure ⁴J(C?O, C-4) in vanillin and ⁴J(C-γ, C-4) in ethyl ferulate. The determination of ^1,2,3,4J (CH) absolute values was done by means of gated decoupled ¹³C spectra of the non-labelled compounds. When second order effects made the use of this technique impossible we determined certain J(CH) values and their signs either by analysing the ¹H NMR spectra of ¹³C labelled coniferyl alcohol [²J(C-β, H-γ), ²J(C-β, H-α), ²J(C-γ, H-β), ³J(C-γ, H-α)] or by a double irradiation experiment on the 250 MHz ¹H NMR spectrum of ethyl [β-¹³C] ferulate [for ²J(C-β, H-γ)].     

Unusually large deuterium isotope effects on one-bond 13C, 1H coupling constants in trans-stilbene challenged

The reported apparent large decrease in ¹J(C-α, H-α) by 1.75±0.20 Hz on replacement of one of the olefinic protons by deuterium in trans-stilbene is due to improper first-order analysis of the ¹H-coupled ¹³C spectrum of the parent compound. Consequently, the implied conformational difference between trans-stilbene and α-deuterio-trans-stilbene, which was used to explain the result, is not substantiated.     

13C NMR study of some polychloro-isobutane and -isobutene compounds

The ¹³C chemical shifts and the carbon–proton coupling constants have been determined for some chlorinated isobutane and isobutene compounds. The one-bond coupling constants in isobutane derivatives showed a regular increase with an increasing number of γ-chlorine substituents. The three-bond coupling constant of the methyl carbon decreased from 4.2 to 2.0 Hz as the number of chlorine substituents in the γ-position increased. In the isobutene compounds, the vicinal coupling of C-1 was larger to protons in a group that is trans with respect to a chlorine substituent on C-1 than to those in the corresponding group cis to the chlorine. The vicinal coupling constants between atoms in geminal groups (on C-2) seem to be affected by the orientation of the chlorine substituent on C-1.     

Carbon-13 nuclear magnetic resonance spectroscopy—VII:para-substituted fluorobenzenes

C-13 and F-19 NMR spectra of seventeen para-substituted fluorobenzenes were measured and the chemical shifts as well as coupling constants with respect to substituents were analysed. The chemical shifts of the fluorine, the C₁ and the C₂ atoms were found to depend on the total electron densities. In the case of the C₃ atom, the chemical shifts seem to depend on π-electron densities rather than the total electron densities. The present calculations also indicate that the chemical shift of the C₄ atom depends mainly on σ-electron densities due to the inductive effects of substituents. The strongest factor influencing the coupling constant, ⁿJ(C? F), is also considered to be the π-electron densities on the carbon atoms. In the case of the direct couplings, ¹J(C? F), the π-bond orders are important.     

Long range 13C?1H coupling constants IV—methoxy-, amino- and hydroxypyridines

One bond and long range ¹³C? ¹H coupling constants for some methoxy-, amino- and hydroxypyridines are described. An unambiguous assignment of carbon-13 resonances is carried out based on the analysis of the fine splitting caused by long range couplings. J values for compounds other than 2- and 4-hydroxy-pyridines are explainable in terms of the values previouly obtained for cyano- and methylpyridines. The hydroxypyridine-pyridone tautomerism affects ²J(H_α), i.e. ²J associated with the α proton. This effect can be used to differentiate pyridones from hydroxypyridines.     

Carbon-13, proton spin–spin coupling constants in some 2-substituted propanes

Carbon-13, proton coupling constants have been measured in eighteen different 2-substituted propanes. ¹J(C-2,H) shows variations similar to those observed previously for monosubstituted methanes. ²J(C-2,H) is essentially independent of the substituent at C-2, while ²J(C-1,H) varies over a range of at least 5 Hz. The latter coupling constant becomes more positive as the electronegativity of the substituent increases while ³J(CH) decreases as the electronegativity of the substituent increases. The observed trends in ⁿJ(CH) are compared with those calculated using semi-empirical molecular orbital theory at the INDO level of approximation.     

Signs of proximate 31P, 19F and 19F, 19F spin–spin coupling constants in 2-trifluoromethylphenyldifluorophosphine

In 2-trifluoromethylphenyldifluorophosphine the proximate couplings ⁴J(¹⁹F³¹P) and ⁵J(¹⁹F¹⁹F) are + 68.3 and + 8.3 Hz, respectively. ¹J(¹³C³¹P) is ?57.0 Hz, ²J(¹³C-1, ¹⁰F) is + 9.9 Hz and ²J(¹³C-6, ¹³C-6, ³¹P) is + 10.1 Hz. The trifluoromethyl substituent induces substantial changes in some coupling constants, particularly those between the ³¹P and ring ¹³C nuclei.     

Carbon-13 NMR spectra of saturated heterocycles: XI—Tetrahydropyrans (oxanes)

The ¹³C NMR spectra of 62 oxanes (tetrahydropyrans) with and without methyl substituents at various ring positions, some of them bearing in addition (or instead) ethyl, vinyl, ethynyl, carbomethoxy and methylol substituents at C-2, have been recorded, and the 294 resulting chemical shifts have been correlated by multiple linear regression analysis. Axial and equatorial α-, β-, γ-, δ-, gem- and vic-parameters for shifts caused by methyl groups at all ring positions, and similar parameters for Et,—CH?CH₂,—C?CH, CO₂Me and CH₂OH groups at C-2, are reported. Standard deviations of the parameters are, in most cases, within 0.3 ppm and the agreement of calculated and experimental shifts is excellent. This is probably the largest parameter set of this type extant. ¹³C NMR spectra of a number of additional substituted tetrahydropyrans, and of 3,6-dihydro-2H-pyrans and 3,4-dihydro-2H-pyrans, are tabulated and discussed.     

Carbon-13 nuclear magnetic resonance studies of creatine,creatinine and some of their analogs

Creatine (N-methyl-N-amidinoglycine), creatinine (1-methyl-2-aminoimidazolin-4-one) and a series of 38 of their close structural analogs have been examined using natural abundance ¹³C NMR spectroscopy at 25.16 MHz. Both proton-coupled and proton noise-decoupled spectra were recorded. Unequivocal assignments of the carbon resonances could be made in the vast majority of cases. Both ¹³C NMR chemical shifts and ¹J(CH) values can be used to characterize and to differentiate readily between analogs of creatine and analogs of creatinine. For example, the ¹J(CH) coupling constants for the α-carbons of the acyclic creatine analogs were all in the 140–142 Hz range, whereas the corresponding coupling constants for the related, cyclized creatinine analogs were all in the 150–152 Hz range.     

Carbon-proton coupling constants in α-chlorostyrene-α-13C

The two stereochemically distinct two-bond carbon-13- hydrogen coupling constants J(¹³C? CH), for α-chlorostyrene-α-¹³C have been shown to be of similar magnitude but opposite sign (?6.3 and +5.6 Hz). A simple additivity relationship which adequately reproduces all the reported J(¹³C? CH) values for chloroethylenes has been found.     

Synthesis of indolo-α-pyrones,indolo-α-pyridones,and indolopyrylium salts

A method has been developed for obtaining indolo--pyrones by acylation of 3-indolylacetic acid and its N-methyl derivatives. Indolo--pyrones form indolo--pyridones by refluxing with ammonium acetate in acetic acid. Indolo[2,3-c]pyrylium salts were obtained by acylation of 4-methoxyand 3,4-dimethoxy-3-phenacylindoles.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 345–349, March, 1971.     

An 1H and 13C NMR study of pentane-2,4-dione tellurium(II) compounds; chemical shifts, 125Te?1H and 125Te?13C couplings

¹H and ¹³C NMR data are reported for pentane-2,4-dione tellurium(II) compounds which contain a 6-membered tellurane ring bearing methyl or ethyl substituents. The ¹²⁵TeCH coupling constants are particularly interesting in that they are highly stereospecific, viz. ～60 Hz and 0–8 Hz for equatorial and axial protons, respectively, in the chair conformation. ¹J(TeC) and ²J(TeCC) couplings lie in the ranges 118–146 Hz and 44–49 Hz, respectively. Geminal HCH couplings in these compounds (9–11 Hz) are lower than analogous values in tellurane or in cyclohexane-1,3-diones.     

High resolution 1H NMR spectra of 2,2′-biquinoline

From analysis and refinement by the LAOCOON III program of the 220 MHz ¹H spectrum of 2,2′-biquinoline, recorded as a saturated solution in carbon disulphide, most derived chemical shifts and coupling constants are close to corresponding values in quinoline. However, H-3 is at 1.5 ppm lower field in 2,2′-biquinoline than in quinoline and the ortho-coupling ³J(34) in the heterocyclic ring is 0.5 Hz larger in 2,2′-biquinoline than in quinoline; fairly free rotation about the 2,2′ bond is inferred.