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.     

Investigation of substituent effects of chalcones by 13C n.m.r. spectroscopy

¹³C chemical shifts for 23 para- and meta-substituted chalcones of the types 1 and 2 have been determined. The aromatic shieldings are compared with previous results for other aromatic derivatives. Correlations of the ¹³C chemical shifts of vinyl carbons and carbonyl carbons as well as ring carbons with Hammett σ parameters, π electron densities and the reactivity parameters of Swain and Lupton provide a consistent picture of electronic effects transmitted through the carbon framework of the compounds studied.     

Investigation of Substituent Effects on Proton and Carbon-13 Chemical Shifts of 4-Substituted Trans-Stilbenes

Proton and carbon-13 chemical shifts of para-substituted stilbenes have been measured. ¹H-¹H, ¹H-¹³C COSY spectra were obtained to analyze unambiguously the chemical shifts of protons and carbons. A long range coupling between 2-H and α-H was observed in a ¹H-¹H COSY spectrum. The observed chemical shifts have been correlated with Hammett substituent parameters. Among ethenyl protons and carbons, all but the chemical shifts of α-H show good correlation with both dual substituent parameters and single substituent parameters. In addition to this finding, the excellent linear correlations of C-l, and 4′-H of 4-substituted trans-stilbenes are also reported. Besides the correlations of chemical shifts with Hammett parameters, a good correlation between the chemical shifts and the calculated charges of position C-4′ are reported.     

Carbon-13 NMR spectra of some 4-substituted phenacyl bromides

The ¹³C NMR signals for some 4- substituted phenacyl bromides were assigned. The experimental chemical shifts of the aromatic ring carbons are in close agreement with those calculated using substituent chemical shifts. Both the carbonyl and the α-methylene carbons exhibit upfield shifts compared with those of the corresponding 4-substituted acetophenones.     

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.     

Dual substituent parameter analysis of the ethyl and ipso 13C n.m.r. chemical shifts of some ring-substituted ethylbenzenes and ethylnaphthalenes

The natural abundance ¹³C n.m.r. spectra of a series of para-substituted ethylbenzenes, 4-substituted-1-ethylnaphthalenes and a limited series of 6-substituted-2-ethylnaphthalenes have been examined at low dilution in deuterochloroform solvent. The ethyl carbons and C_ipso in the phenyl series (i.e. have been assigned, and substituent chemical shifts for these carbons calculated and analysed by the Dual Substituent Parameter treatment. (Chemical shifts of all ring carbons have been obtained, but not assigned). Generally speaking, electron-withdrawing substituents lead to positive (i.e. downfield) substituent chemical shifts for CH ₂ and negative substituent chemical shifts for C H₃, i.e. ‘normal’ and ‘inverse’ behaviour respectively. C_ipso in the phenyl series exhibits a ‘normal’ dependence. The dependences of the various substituent chemical shifts on inductive and resonance parameters are discussed, and compared with the behaviour of side chain carbons in other substituted benzene systems.     

Carbon-13 nuclear magnetic resonance studies of anthraquinones. Part III—correlation of substituent effects for 2-substituted anthraquinones

The ¹³C chemical shifts of 2-substituted and 2,6-disubstituted anthraquinones have been determined and assigned. The C-1, 2, 3, 4, 13 and C-14 chemical shifts of 2-substituted anthraquinones are correlated with the chemical shifts of monosubstituted benzenes. A three-parameter correlation with Swain and Lupton's ? and ? parameters and Schaefer's Q parameter provides relationships for the prediction of all chemical shifts of 2-substituted anthraquinones from the substituent parameters. Q values for the SCH₃, OCOCH₃, C₂H₅ and C(CH₃)₃ groups are proposed. The two types of correlations are compared for predicting chemical shifts.     

Carbon-13 NMR studies on some 5-substituted quinoxalines

Eleven 5-substituted quinoxalines (NO₂, NH₂, COOH, OCH₃, CH₃, OH, F, Cl, Br, I, CN, the latter five not reported previously) have been synthesized by standard methods. Their ¹³C NMR spectra have been measured in DMSO-d₆ and assigned on the basis of substituent parameters, by line widths and by intensities. The chemical shifts compare favorably with those calculated using benzene substituent parameters, and are very close to those of corresponding carbons in 1-substituted phenazines. The correlation with the chemical shifts of the corresponding positions in 1-substituted naphthalenes is also close except for those of carbons 4a and 8a in the quinoxalines which, due to their proximity to nitrogen, are downfield (in some cases 12 ppm) of the signals of the corresponding carbons in naphthalene. 5-Fluoroquinoxaline was also measured in CDCl₃, CD₃COCD₃, CD₃CN, CD₃OD, C₆D₆ and CD₃COOD. In all solvents an abnormally low ²J(CF) (～ 12 Hz) was found for C-4a and no C? F spin-spin splitting could be detected for the three-bond coupling of C-8a. Similar abnormalities were found in 2-fluoroaniline and 2-fluoroacetanilide. There are linear relationships between the Q parameter of the substituent and the chemical shift of carbons 4a, 5 and 6. A linear relationship also exists between the chemical shift of C-8 (‘para’ position) and the Hammett σ_p parameter of the substituent.     

Geometrical isomerism and 13C spectra of the β-substituted Enones R1?C(1)O?C(2)HC(3)H?R2

The ¹³C chemical shifts of the unsaturated carbons were measured in 31 cis and trans pairs of β-substituted enones R₁? C(1)O? C(2)H?C(3)H? R₂. In these polarized ethylenes the chemical shifts of the olefinic carbons are simply related by the equation δ_c=δ_t+A. The steric and electronic effects introduced by the R₁ and R₂ substituents influence the chemical shifts of C-2 and C-3 in both isomers. It is shown that the sign and magnitude of the intercept A mainly reflect the π-charge electronic density changes which arise in the cis isomer and are transmitted via the π-framework. The effect of the steric interaction on the chemical shift of C-3 in the cis isomers is postulated to be related to the symmetry of the substituents. Therefore, the differential shielding of C-3 is indicative of the conformational structure of the cis molecule.     

Influence of substituents on carbonyl carbon chemical shifts in 4-substituted bornane-2,3-diones and the preparation of bornane-2,3-dione

¹³C Chemical shifts of the 4-substituted boniane-2,3-dione(1–6) have been assigned. The shielding of the CO carbons brought about by electron withdrawing substituents is attributed to a field effect of the substituent which serves to increase the CO bond order. For the substituent bearing carbons C(4), enhanced shielding is noted and these carbons exhibit small substituent chemical shifts. A preparative method leading to borane-2,3-dione is described and briefly discussed.     

Carbon-13 nuclear magnetic resonance spectroscopy. Substituent-induced chemical shift effects on cyclopropyl carbons of 4-substituted cyclopropylbenzenes

Carbon-13 chemical shifts of the cyclopropyl carbons of eleven 4-substituted cyclopropylbenzenes have been measured under conditions effectively corresponding to infinite dilution in DCCI₃. The substituent-induced chemical shifts (SCS) of both the α and β carbons of the cyclopropane ring were found to be downfield with electron-attracting groups and upfield for electron-donating groups. The trends for the β carbons correspond to those observed for the β carbons of 4-substituted phenylethenes, while the trends of the α carbons are similar to those found for the α carbons of 4-substituted isopropyl benzenes. The results for the β carbons can be rationalized by postulating a substantial contribution from a hyperconjugative resonance effect involving the σ system of the benzene ring (and its 4-substituent) and the C-α—C? β bonds of the cyclopropane ring. The effects on the α carbons are in accord with a very reasonable smaller inductive polarization of the C-α? C-β bonds than encountered for the carbons of corresponding ethenyl- or ethynylbenzenes.     

Substituent effects on carbon-13 NMR chemical shifts of side chain carbonyl carbons of 4-substituted 1-naphthamides

Substituent induced¹³C NMR chemical shifts of side chain carbonyl carbons of several 4-substituted 1-naphthamides have been measured in DMSO-d ₆ solvent. Analysis of the substituent induced chemical shifts by the DSP equation gave the regression equation. Both {ie207-1} and {ie207-2} values were negative. The negative sign on {ie207-3} term indicates the operation of a reverse substituent effect and that π-polarisation is the important mechanism for the transmission of substituent effects by inductive effect. Theperi-hydrogen interaction in naphthamides forces the amide group out of the plane of the naphthalene ring.     

13C NMR study of ortho-, meta- and para- substituted phenyldiphenylamines: Substituent effect correlations

The ¹³C chemical shifts of 11 substituted triphenylamines have been determined and the assignment of these resonances made using intensities, ¹H and ¹⁹F couplings and predictions from bond additivity relationships. ¹³C chemical shifts at carbons bearing the substituent and at carbons ortho to the substituent correlated reasonably well with the Q parameter. A multiple regression analysis of chemical shifts with the field and resonance parameters of Swain and Lupton and the Q parameter produced significantly better correlations than those obtained when Q was omitted for these positions. ¹³C chemical shift correlations for carbons meta and para to the substituent were not significantly better than when Q was omitted. Significant correlations were obtained between field and resonance parameters and ¹³C chemical shifts of C-o and C-p, and C-i, C-o, C-m and C-p of the non-substituent bearing phenyl rings in ortho- and para-substituted phenyldiphenylamines, respectively.     

Carbon-13 NMR studies of a series of benzylphenols

Carbon-13 NMR spectra of a series of benzylphenols and their O-alkylated derivatives were recorded to find the substituent effects of the benzyl, hydroxybenzyl and alkoxybenzyl groups on the ¹³C chemical shifts. It was found that the methylene bridge carbons show signal shifts mainly due to the mesomeric effects of the OH and OCH₃ substituents, and that in the case of ortho-substituted benzyl compounds, the methylene carbon signals exhibit upfield shifts due to both mesomeric and steric effects.     

13C Pulse fourier transform NMR of menthol stereoisomers and related compounds

¹³C NMR spectra of menthol stereoisomers have been determined. The correlations of chemical shifts of these ring carbons with those of stereoisomeric 2-isopropylcyclohexanols are examined. Observed chemical shifts of 1-Me carbons are compared with those predicted from the chemical shifts of stereoisomeric 1-methyl-4-t-butylcyclohexanes. ¹³C NMR spectra of menthyl acetates, and cis and trans p -menthanes have also been examined.     

13C-NMR-spektren von di- und trinuclearen polymethincyanin-farbstoffen

¹³C NMR chemical shifts are reported and assigned for two vinylogous series of polymethinecyanine dyes with indolenine- and benzothiazole nuclei. The influence of the heterocyclic groups and the chain length upon the chemical shifts of the methine carbons and upon the corresponding ¹J_¹³C¹H-coupling constants has been studied. ¹³C chemical shifts of indolenine derivatives correlate with calculated π-electron densities. The combined application of ¹H- and ¹³C NMR spectroscopy turns out to be a useful method for detecting steric hindrance in polymethine dyes.     

13C-NMR-Spektren von γ-substituierten pentamethincyanin-farbstoffen mit indolenin-endgruppen

The ¹³C-resonances of fourteen γ-substituted pentamethincyanine dyes 1 with indolenine nuclei have been measured and assigned. The effect of the γ-substituents R on the ¹³C chemical shifts is compared with the corresponding effect of substituents R of monosubstituted benzenes and 1-substituted trans-butadienes. The chemical shifts of the C²-methincarbons, which are separated by four bonds from R, correlate with Hammett's substituent parameters σ_para. A significant substituent effect through nine covalent bonds has been observed.     

1H, 13C and 77Se NMR spectra of substituted selenoanisoles

The ¹H, ¹³C and ⁷⁷Se chemical shifts and the ¹J[C(Me)H(Me)], ^1.2J(SeC) and ²J(SeH) coupling constants in 14 para- or meta-substituted selenoanisoles, R? C₆H₄? Se? CH₃, have been measured and the dependence of these parameters on the electronic effects of the substituent R is discussed. A significant (up to 6 ppm) deviation from additivity of the substituent influence on the shielding of the ¹³C ring carbons has been found.     

Proximity and the heteroatom effects on the carbon-13 chemical shifts of methyl-substituted phenols,anilines and thiophenols

Upfield substituent-induced ¹³C chemical shifts for aryl carbons of polymethyl substituted benzenes, phenols, anilines and thiophenols were investigated as a function of the proximity between substituents X and CH₃ (X = CH₃, NH₂, OH and SH). The results indicate that the induced shifts of the substituted aryl carbons are, in general, independent of the polar substituent but depend on the number of adjacent substituted aryl carbons. A ?2.0 ppm upfield shift was found for a substituted aryl carbon adjacent to one substituted aryl carbon and a ?3.8 ppm upfield shift for a substituted aryl carbon bound by two substituted aryl carbons. It is suggested that the near additivity of the upfield shifts is the result of changes in the bond order between the aromatic ring carbons in the region of the substituted aryl carbons due to distortion of the ring. The ¹³C chemical shifts of the methyl substituents for methyl substituted phenols, anilines and thiophenols were determined, and it was found that the values could be predicted from the additivity parameters reported for the analogous methylbenzenes plus an additional pair-interaction term associated with the through-space electronic influence of the heteroatom.     

13C NMR STUDY OF SUBSTITUENT EFFECTS IN 1,2,4-OXADIAZOLE AND 1,2,4-THIADIAZOLE DERIVATIVES

¹³C chemical shifts of C═N, C═O and C═S carbons of 3,4-disubstituted-1,2,4-oxadiazole-5-ones(thiones) and 3,4-disubstituted-1,2,4-thiadiazole-5-ones have been determined in CDCl₃ solution. Exceptionally good Hammett correlations of ¹³C NMR chemical shifts of these carbons with σ were obtained. The negative ρ values observed (inverse substituent effects) indicate π-polarization of the C═N, C═O and C═S bonds. As expected, the long distance C═O and C═S ¹³C chemical shifts were found less susceptible to substituent-induced electronic changes.