13C chemical shifts of monosubstituted adamantanes

¹³C chemical shifts are reported for adamantane, nine 1-substituted adamantanes and nine 2-substituted adamantanes. The substituents are F, Cl, Br, I, NH₂, OH, CH², CN and CO₂H. The assignments and results are discussed in terms of chemical shift patterns.     

Carbon-13 chemical shifts of substituted nortricyclenes

¹³C NMR spectra of a series of substituted nortricyclene derivatives have been measured, and the ¹³C chemical shifts interpreted in terms of α, β, γ and δ-effects. The nature of these substiuent shifts is discussed together with some analytical possibilities. The substituent shifts provide valuable data about the steric effects in strained molecules and can be used as increments for structural analysis, particularly for the determination of orientations of substituent groups.     

Carbon-13 chemical shifts of bicyclic compounds

¹³C NMR absorption spectra of 50 bicyclic hydrocarbons, alcohols and ketones have been measured, in addition to some terpenes. The ¹³C chemical shifts are approximately additive for similar compounds and can be used for the determination of molecular structure; they differ for endo- and exo-isomers, just as in proton spectra. These quite regular and predictable ¹³C shift differences are much larger and are caused by the 1,4-nonbonded interaction between atoms heavier than hydrogen, not by magnetic anisotropy effects.     

Carbon-13 chemical shifts and conformations of dimethylcyclohexanols

Carbon-13 chemical shifts of all twenty-two dimethylcyclohexanols, formed by the hydrogenation of isomeric xylenols, have been measured and assigned. Conformational peculiarities of dimethylcyclohexanols are discussed on the basis of their carbon-13 chemical shifts.     

Carbon-13 chemical shifts of inverted carbon atoms

The inverted carbons in 2,4-methano-2,4-dehydroadamantane are shielded by 14.3 ppm relative to the corresponding carbons in 2,4-methanoadamantane. This was explained by the balance of the inverted carbon hybridization deshielding, the shielding effect of the cyclopropane rings formed, and the change in the influence of the neighbouring atoms.     

Carbon-13 chemical shifts of some propargyl alcohol derivatives

The natural abundance ¹³C chemical shifts of a range of propargyl alcohol derivatives have been determined and individual resonances assigned. The shielding effects of the triple bond and hydroxyl group on neigbouring carbons have been characterised. The observed for these compounds are compared to those of alkyl or allyl alcohols.     

Carbon-13 NMR spectra of monosubstituted pyrazines

Carbon-13 NMR chemical shifts and one-bond carbon–hydrogen coupling constants have been obtained at 15·09 MHz. The trends in the carbon chemical shifts obtained for the pyrazines parallel those of monosubstituted benzenes and 2-substituted pyridines, except for the direct effect of substitution where the pyrazines resemble pyridines not benzenes. The substituent effects on the ¹³C NMR spectra are generally quite similar to those in the ¹H NMR spectra. The ¹³C NMR spectrum of the tautomeric hydroxypyrazine has been compared with the ¹³C NMR spectra of 2-, 3- and 4-hydroxypyridines. Hydroxy compounds that can exist as a cyclic amide show a large meta substituent effect on the chemical carbon shift.     

Carbon-13 chemical shifts of some cholinergic neural transmission agents

Carbon-13 chemical shifts have been obtained in the pulse Fourier transform mode on the following cholinergic neural transmission agents: acetylcholine, β-methyl acetylcholine, carbamoyl choline, choline, tetramethylammonium, scopolamine, atropine, methyl atropine, tropine, tropic acid, nicotine, dimethyl phenylpiperazinium, arecoline, oxotremorine and pilocarpine. The effects of structural variations, asymmetric centers and steric interactions on the ¹³C shielding are considered. The observed chemical shifts do not appear to correlate simply with potencies in the cholinergic nervous system.     

Carbon-13 chemical shifts of some model carboxylic acids and esters

Selected model carboxylic acids and esters dissolved in deuteriochloroform have been studied by carbon-13 nuclear magnetic resonance under standardized conditions. Assignments of the chemical shifts have been made for all samples, and the spin–lattice relaxation times and nuclear Overhauser effects measured for a few selected esters. The results are intended to provide a practical aid for the analysis of carboxylic acids and esters of a more complex nature (e.g. polymers, natural products, etc.).     

Carbon-13 NMR chemical shifts in some substituted 1,2,4-triazol-3-ones

Carbon-13 NMR data for 15 substituted 1,2,4-triazol-3-ones are presented and discussed with regard to enolization in the neutral molecules. The coupling constant and chemical shift data show that the proton at N-2 is not exchanging rapidly in the DMSO-d₆ solvent. Using D₂O? OD^? as a solvent, it is found that the C-3 and C-5 resonances are shifted downfield by nearly the same amount, suggesting that the proton at N-4 is being removed. Enolization in the neutral molecules does not occur to any significant extent.     

Spatial substituent effects of various fluorinated groups on the 13C chemical shifts in cyclohexanes

The effect of introduction of fluorinated groups (CH(2)F, CHF(2), CF(3), C(2)F(5), OCF(3), SCF(3)) on the (13)C NMR chemical shifts in cyclohexanes is examined. The two main effects are caused by location at the alpha and gamma carbon positions. Comparison of the various data allowed the calculation of increments corresponding to the introduction of fluorinated groups at axial or equatorial positions on the cyclohexane ring. The introduction of fluorine atoms in methoxy and thiomethoxy groups has only a slight effect through the heteroatom on the (13)C chemical shifts.     

Carbon-13 chemical shifts and coupling constants in cis- and trans-1,2-di-tert-butylethylene

The spectral parameters of the title compounds were redetermined to resolve discrepancies between data reported in the literature.     

Carbon-13 nuclear magnetic resonance spectroscopy IX—monosubstituted ethylenes

Carbon-13 chemical shifts of sixteen monosubstituted ethylenes were obtained. In order to explain the chemical shifts, σ and π electron densities of these compounds are calculated by the σ-included ω-HMO method.

1 See Ref. 8.

A linear relationship exists between carbon-13 chemical shifts and the calculated electron densities, and also between substituent constants and electron densities. A slope of unity is obtained between the chemical shifts of α carbons of monosubstituted ethylenes and those of carbons adjacent to the substituents in monosubstituted benzenes. On the other hand, a plot of chemical shifts of C_ortho of benzene derivatives against that of the β carbon in ethylene derivatives gives a slope of 3. These slopes can be explained by the calculated electron densities. A slope of 4/3 is obtained between the direct coupling constant ¹J(C? H) of the α carbon in monosubstituted ethylenes and that in the corresponding substituted methanes.     

Carbon-13 nuclear magnetic resonance chemical shifts and 13C-199Hg coupling constants for symmetrical dialkylmercurials

The carbon-13 chemical shifts and coupling constants (J[¹³C? ¹⁹⁹Hg]) have been determined for a series of eleven symmetrically substituted organomercurials. Empirical substituent parameters can be calculated which correlate observed and predicted chemical shifts for dialkylmercurials.     

Vicinal deuterium perturbations on hydrogen NMR chemical shifts in cyclohexanes

The substitution of a deuterium for a hydrogen is known to perturb the NMR chemical shift of a neighboring hydrogen atom. The magnitude of such a perturbation may depend on the specifics of bonding and stereochemical relationships within a molecule. For deuterium-labeled cyclohexanes held in a chair conformation at -80 degrees C or lower, all four possible perturbations of H by D as H-C-C-H is changed to D-C-C-H have been determined experimentally, and the variations seen, ranging from 6.9 to 10.4 ppb, have been calculated from theory and computational methods. The predominant physical origins of the NMR chemical shift perturbations in deuterium-labeled cyclohexanes have been identified and quantified. The trends defined by the Delta delta perturbation values obtained through spectroscopic experiments and by theory agree satisfactorily. They do not match the variations typically observed in vicinal J(H-H) coupling constants as a function of dihedral angles.     

The role of linear electric field effects in halogen induced 13C chemical shifts in cyclohexanes and methylenecyclohexanes

The ¹³C NMR chemical shifts of methylenecyclohexane at low temperature are compared with those of 4-chloro- and 4-bromo-methylenecyclohexane under the same conditions. It is concluded that the halogen induced shift differences at the double bond are to be ascribed largely to linear electric field (LEF) effects. At the same time, doubt is expressed concerning similar explanations for C-4 in halo-substituted cyclohexanes. The large influence of using different values of longitudinal bond polarizabilities is demonstrated. Finally, some remarkable long-range shift effects on double bonds are described for geranyl chloride and geranyl bromide.     

Carbon-13 chemical shift assignment of E-Hydroxyazastilbenes

The ¹³C NMR spectra of nine isomeric E-hydroxyazastilbenes (E-hydroxystyrylpyridines) have been fully assigned. The Ai and AiK empirical parameters of o-(m or p-)hydroxystyryl and 2-(3- or 4-)vinylpyridyl groups for the prediction, of chemical shifts of substituted styrylpyridines were calculated.     

Carbon-13 substituent chemical shifts of 4-substituted bicyclo[2.2.2]oct-1-yl cyanides

The carbon-13 substituent chemical shifts of 4-substituted bicyclo[2.2.2]oct-1-yl cyanides are a linear function of the substituent inductive parameters.