Carbon-13 magnetic resonance: γ-anti substituent effects

γ-anti Substituent effects of the first row elements (CH₃, NH₂, OH, F) and the higher-row halogens on ¹³C chemical shifts are shown to have separate linear relationships with element electronegativity. The halogens generally show an increasing upfield shift with increasing electronegativity, but the response of the effect of the first-row elements to changing electronegativity is dependent upon the substitution pattern of the atoms involved. In molecules with the substituent at a bridgehead, increasing electronegativity causes increasing downfield shift of the γ-anti carbon, whereas in other systems which have the substituent at a secondary carbon, increasing electronegativity causes an increasing upfield shift. Examples are cited to show that the γ-anti effect of a hydroxyl group is more shielding (by about 2 ppm) when a 1,3-diaxial interaction between an α and a γ hydrogen is present, than when this interaction is removed by replacement of either of the hydrogens. This correlation is taken as evidence of this hydrogen-hydrogen interaction as one pathway for the transmission of the γ-anti substituent effects of first-row elements.     

Carbon-13 nuclear magnetic resonance spectra. VIII—18α- and 18β-glycyrrhetic acid derivatives

The ¹³C NMR data of six pairs of 18α/18β-glycyrrhetic acid derivatives are presented. It is shown that the configuration at C-18 can easily be recognized by inspecting the chemical shifts of several characteristic carbons, e.g. C-12, C-13, C-18 and C-28. The shifts of these carbons originated by the change of the D/E ring junction proved to be largely independent of the substitution at C-3 and C-20.     

Photochemical naphthylation at(α-carbon atom of carbonyl and its equivalences

The photostimulated reaction of halonaphthalene with a series of carbanions derived from,propionic acid derivatives in liquid ammonia led to the naphthylation at a-carbon of the carbanions inan isolated yield ranging from 25％ to 86％.In all cases,the dehalonaphthalenes were found to,be by-products and the reaction was inhibited by p-dinitrobenzere.An electron transfer from thecarbanion to the halonaphthalene followed by ejection of halogen led to naphtbyl radical,as predictedby comparing the LUMOs of the carbanions and the halonaphthalenes,was involved in the process.Absence of the alkylnaphthalene and 1,2-dinaphthylalkane in the products indicates the smoothelectron transfer between(Naph-Nu)~+ and Naph-X.C-vs.O-naphthylation is fully addressed interms of MNDO calculations and acid-base principle.     

The temperature dependence of the 13C nuclear magnetic resonance spectra of porphyrins

The high temperature ¹³C NMR spectra of the methyl esters of deuteroporphyrin-IX and protoporphyrin-IX, and octaethylporphyrin show sharp discrete signals for the inner macrocycle carbon resonances. The temperature dependence of these shifts is discussed.     

Electronegativity and linear electric field effect on γ-anti 13C chemical shifts

The contribution from the existence of a 1,3-diaxial H-α ?H-γ arrangement to the γ-anti effects of substituents X, which was previously believed to be generally shielding, is shown to be extremely dependent on the electronegativity of substituent X. In the presence of axial γ-substituents Y, linear electric field effects appear to play a significant role if the C-γ—Y bond is highly polarizable.     

Carbon-13 nuclear magnetic resonance spectra: V—substituent interactions at 4-substituted adamantanones and bicyclo[2.2.2]octanones

The ¹³C n.m.r. data of a variety of 4_eq- and 4_ax-substituted adamantanones and bicyclo[2.2.2]octanones are presented. It is shown that for a number of carbons the chemical shifts cannot be predicted by a given additivity rule. The deviations of the observed chemical shifts from the calculated ones are discussed in terms of different interaction mechanisms operating through the σ bond frameworks or through space.     

13C nuclear magnetic resonance spectra—VII: Through-bond interactions and hyperconjugative substituent effects at 2,4-disubstituted adamantanes

The ¹³C NMR spectra of a series of 2,4-disubstituted adamantanes with the substituents in various configurations are reported and discussed in terms of through-bond and through-space interactions of the substituents. Through-bond interactions in equatorially disubstituted adamantanes and equatorially substituted adamantanones are attributed to overlapping of free-electron pairs and bond orbitals in symmetrically favoured orientations.     

Carbon-13 nuclear magnetic resonance spectra: III—2-heteroadamantanes

The ¹³C n.m.r. spectra of some 2-heteroadamantanes and 1-substituted 2-heteroadamantanes are reported. The influences of the heteroatoms in the adamantane framework, and those of the substituents attached to it, on the ¹³C chemical shifts of the adamantane carbons are investigated and compared with related compounds such as the corresponding heterocyclohexane derivatives and 2-mono- and 2,2-disubstituted adamantanes. The nonadditivity of the substituent effects for 1-substituted 2-heteroadamantanes, especially for the geminally substituted carbons, is substantially confirmed. In addition, the influences of a missing CH₂ group and of NCH₃ carbons upon the ¹³C chemical shifts of the carbons in the adamantane system are described.     

A revised assignment of the 13C NMR spectra of α- and β-pinenes

α-Pinene and β-pinene ¹³C enriched at the C-10 position were prepared by an unambiguous synthesis. ¹³C NMR spectral analysis provided evidence for a revised assignment for α-pinene at the C-9 and C-10 carbon atoms.     

Carbon-13 nuclear magnetic resonance spectra. I—Monosubstituted adamantanes and adamantanones

The chemical shifts of 4_ax and 4_eq substituted adamantanones are compared with those calculated with the aid of a given additivity rule. It is found that both δ carbons are shielded with respect to the substituent. In contract to the situation for the y-atoms, however, the δ_syn atom is less shielded than the δ_anti atom. In most cases the additivity rule predicts the chemical shifts with an accuracy of approximately 1 ppm. Exceptions are carbon atoms 4 and 9 of the 4_eq substituted adamantanones. In both cases the measured values are 4 to 6 ppm upfield. This can possibly be explained by an electronic interaction between the carbonyl group and the substituent.     

13C nuclear magnetic resonance of organophosphorus compounds XI—aminophosphines

Natural abundance ¹³C NMR studies have been carried out on a series of organophosphorus compounds possessing P? N bonds. For the first time a one-bond temperature-dependent ¹³C—³¹P nuclear spin coupling was observed for the P-phenyl carbons in bis(N,N-dibenzylamino)phenylphosphine (0-9 Hz) and bis(N,N-diethylamino)phenylphosphine (0–2 Hz). This temperature-dependent behavior can be rationalized in terms of free rotation about the phenyl phosphorus bond with concomitant hindered rotation about the P? N bonds. A conformational preference for the nitrogen and phosphorus lone pairs to exist in the trans orientation is indicated. In the similarly substituted 5-membered heterocyclic ring compound, 1,3-dimethyl-2-phenyl-1,3-diazaphospholidine, the phenyl one-bond coupling increases to (?) 42.1 Hz and becomes temperature independent. These data suggest that ¹J(PC) is very responsive to electronic effects.     

Investigation of benzimidazoles. III—transmission of the substituent effects in 2-substituted 1-methylbenzimidazoles studied by 13C nuclear magnetic resonance

The influence of substituents on the ¹³C NMR chemical shifts of 2-substituted 1-methylbenzimidazoles has been investigated. The electronic effects of the substituents are transmitted to C-4 and C-7 mainly by the resonance mechanism, and to C-5, C-6 and N-CH₃, by approximately equal contributions of the resonance and inductive components. A critical analysis of the share in the transmission of substituent effects through the ‘pyridine-type’ and ‘pyrrole-type’ nitrogen atoms is given.     

Nuclear magnetic resonance spectra of carbanions—VI. Cumyl-, α-methylbenzyl- and benzyl carbanions

The proton magnetic resonance spectra of the three title carbanions have been observed in THF with potassium as a counter ion. The ortho-protons in the α-methylbenzyl carbanion are nonequivalent at room temperature. This shows that the α-carbon in this carbanion is in the near-sp² configuration. The aromatic proton chemical shifts of the benzylpotassium obtained here are at higher shielding than those of benzyllithium reported previously by Sandel and Freedman. This seems to arise from the different ionic nature of the bonds between carbon and metal in the carbanions.     

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.     

Carbon-13 nuclear magnetic resonance studies of anthraquinones. IV—correlation of substituent effects for 1-substituted anthraquinones

The spectra of various 1-substituted and 1,5-disubstituted anthraquinones have been studied and the chemical shifts of the different carbon nuclei determined. The chemical shifts previously reported for 1-Me-anthraquinone have been corrected and reassigned. The C-1, C-4 and C-13 shifts of 1-substituted derivatives are correlated with the chemical shifts of monosubstituted benzenes. Deviations from the regression lines can be explained by the existence of steric factors and hydrogen bonding. A three-parameter correlation with Swain and Lupton's ? and ? and Schaefer's Q provides relationships for the prediction of all chemical shifts of 1-substituted anthraquinones when the substituents have a cylindrical symmetry.     

A nuclear magnetic resonance (1H and 13C) and isotope ratio mass spectrometry (δ13C, δ2H and δ18O) study of Andalusian olive oils

We have determined δ¹³C, δ²H and δ¹⁸O isotopic abundances in Andalusian olive oils. In addition, the fatty acid composition and the distribution of isomers at positions 1,3 and 2 of glycerol were determined by ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy, respectively. Isotopic results obtained for four series of oil samples extracted from olives harvested in the 2004/05 and 2005/06 seasons are discussed in terms of olive variety, ripeness, geographical origin, fatty acid composition and growing altitude. A distinction was also established between olives grown in irrigated and in dry land by studying selected samples of the previous series and others from the 2005/06, 2006/07, 2007/08 and 2008/09 seasons. The results showed that olive ripeness does not influence the abundance of any of the three isotopes studied. On the other hand, the olive variety influences the abundance of the oxygen and hydrogen isotopes, and also, less markedly, that of carbon. No clear‐cut effect of height or latitude on isotope values is observed, probably because the olive variety also changes with height and latitude, thus masking such influences. The oil samples from dryland‐grown olives had increased δ¹³C values relative to irrigation‐grown olives. In addition, no definite relationship appears to exist between isotope distribution and fatty acid composition. Finally, oil samples from olives harvested in the 2005/06 season in Italy could be distinguished from those from Spain in terms of their isotopic values (δ²H mainly). Copyright © 2010 John Wiley & Sons, Ltd.     

The carbon-13 nuclear magnetic resonance spectra of some α-spirocyclopropyl ketones and related cyclohex-2-en-1-ones and 2-ethylidenecyclohex-3-en-1-ones

The ¹³C NMR spectra of a series of β,γ-unsaturated α-spirocyclopropylcyclohexanones and saturated α-spirocyclopropylcycloalkanones have been analyzed and compared with the spectra of diethyl cyclopropanedicarboxylate and a corresponding spiro acylal. The chemical shifts of the cyclopropane methylene carbons are correlated with spiroactivation of the cyclopropane ring to nucleophilic attack. In the case of the saturated spiro ketones these chemical shifts can also be correlated with their photochemistry. In the SFORD spectra of the spiro ketones the signals of the cyclopropane methylene carbons appear as complex multiplets: this is attributed to second-order coupling resulting from strong coupling between the vicinal cyclopropane protons. The ¹³C NMR spectra of a series of related cyclohex-2-en-1-ones and 2-ethylidenecyclohex-3-en-1-ones have also been analyzed; the chemical shift assignments for the latter corroborate the configurational assignments made on the basis of ¹H NMR spectroscopy.     

13C nuclear magnetic resonance spectra of polyacrylates and their model compounds

¹³C nuclear magnetic resonance spectra (¹³C-NMR) of poly(methyl acrylates) and poly(isopropyl acrylates) of various tacticities were measured at 25.1 MHz and analyzed. ¹³C-NMR spectra of model compounds for poly(methyl acrylate), poly(acrylic acid), and poly(sodium acrylate) were also determined. The spectra of the polymers were generally complicated owing to the splittings corresponding to triad, tetrad, or pentad placements, and the assignment for each peak was difficult. Groups of peaks were analyzed by triad or tetrad placements by assuming Bernoullian or first-order Markovian statistics.