13C NMR studies of methylnucleosides

The ¹³C chemical shifts of 22 methylated ribonucleosides and deoxyribonucleosides have been measured and assigned. The chemical shift differences between methylated and unmodified nucleosides are correlated with their characteristic modifications of structure. The significance of the chemical shift and tautomeric variations is discussed.     

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 NMR spectra of arylnaphthalene lignans

The¹³C NMR spectra have been investigated of a number of arylnaphthalene lignans of plant origin: daurinol and its acetyl derivative and reduction product, justicidin A, justicidin B and its reduction product and the diacetyl derivative of the reduction product, and diphyllin and its acetate. The values of the chemical shifts of the carbon atoms in the spectra of the compounds investigated and the nature of their change according to structural factors are discussed and an assignment is made of the resonance lines in the spectra. The characteristics of the spectrum of one compound are used as models for others. The parameters of the¹³C NMR spectra of a number of naphthalene derivatives are also used. On the basis of the results of the assignment of the signals, difference values of the chemical shifts of the carbon atoms in the series of compounds investigated have been determined. Using the experimental results as a background, some examples taken from the literature of investigations of the¹³C NMR spectra of related compounds have been analyzed.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 76–90, January–February, 1987.     

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.     

13C shielding scale for MAS NMR spectroscopy

We have performed the direct measurements of ¹³C magnetic shielding for pure liquid TMS, solution of 1% TMS in CDCl₃ and solid fullerene. The measurements were carried out in spherical ampoules exploring the relation between the resonance frequencies, shielding constants and magnetic moments of ¹³C and ³He nuclei. Next the ¹³C shielding constants of glycine, hexamethylbenzene and adamantane were established on the basis of appropriate chemical shifts measured in the solid state. All the new results are free from susceptibility effects and can be recommended as the reference standards of ¹³C shielding scale in the magic angle spinning NMR experiments. Copyright © 2011 John Wiley & Sons, Ltd.     

13C NMR spectroscopy of coumarin derivatives

The ¹³C chemical shifts of 209 naturally occurring and synthetic coumarin derivatives are listed and a number of methods for signal assignments are explained. Substituent effects on ¹³C chemical shifts (SCS) in monosubstituted coumarins and non-additivities of SCS in coumarins with more than one substituent are discussed in detail.     

QSAR studies of phenylhydrazine-substituted tetronic acid derivatives based on the 1H NMR and 13C NMR chemical shifts

The quantitative structure–activity relationship models of 40 phenylhydrazine-substituted tetronic acid derivatives were established between the ¹H nuclear magnetic resonance (NMR) and ¹³C NMR chemical shifts and the antifungal activity against Fusarium graminearum, Botrytis cinerea, Rhizoctonia cerealis, and Colletotrichum capsici. The models were validated by R, R², R_A², variance inflation factor, F, and P values testing and residual analysis. It was concluded from the models that the ¹³C NMR chemical shifts of C8, C10, C7, and the ¹H NMR chemical shifts of Ha contributed positively to the activity against Fusarium graminearum, Botrytis cinerea, Colletotrichum capsici, and Rhizoctonia cerealis, respectively. The models indicated that decreasing the election cloud density of specific nucleuses in compounds, for example, by the substituting of electron withdrawing groups, would improve the antifungal activity. These models demonstrated the practical application meaning of chemical shifts in the quantitative structure–activity relationship study. Furthermore, a practical guide was provided for further structural optimization of the antifungal phenylhydrazine-substituted tetronic acid derivatives based on the ¹H NMR and ¹³C NMR chemical shifts.     

The 13C NMR spectra of nine ortho-substituted phenols

The ¹³C chemical shifts of nine ortho-substituted phenols have been determined in cyclohexane and in dimethyl sulfoxide. All data were acquired in duplicate upon c.w. and FT instrumentation and both sets of data are presented. The chemical shifts at carbons 1, 2 and 3 are correlated with the parameter Q. Q has been defined as P/Ir³ where P is the polarizability of the adjacent C? X bond, I is the first ionization potential of the elements F, Cl, Br, I and H, and r is the C? X bond length. Experimental values of Q are available for other substituents. The field and resonance parameters of Swain and Lupton may be combined with Q to form a three part multiple regression correlation which is more exact than that with Q alone and which applies to all carbons in the aromatic ring. The results of this study suggest that only one value of the Q parameter is needed to characterize the behavior of the nitro group in these solvent systems. This conclusion is contrasted with earlier results of the effect of substituents on proton chemical shifts in these systems.     

Analyses of synthetic resins by application of 13C NMR

In a study of synthetic resin analysis, ¹³C NMR spectra of phenol resins were measured, and the chemical shifts of the various carbon sites compared with the resins' reactivity with formaldehyde. Measurements were made with phenol, para-substituted phenols, chlorophenols, hydroxytoluenes, dimethyl(hydroxy)benzenes, dihydroxybenzenes, and dihydroxytoluenes. The chemical shifts of these phenols were compared with calculated shifts obtained by using a simple summing rule. These chemical shifts are closely related in magnitude to the reactivity of the phenols with formaldehyde. For example, resorcin has the greatest reactivity with formaldehyde of the above-mentioned phenols and this experimental result agrees well with the measured large ¹³C chemical shifts for resorcin.     

The13C NMR spectra of some polychlorinated dibenzo-p-dioxins. A calculation of13C chemical shifts

The¹³C NMR spectra of a number of polychiorinated dibenzo-p-dioxins (PCDD) were measured. These and previously known spectra were used for the development of a method for calculation of¹³C NMR spectra of chloroaromatics in the framework of a two-particle increment scheme for carbon chemical shifts. The scheme one allows to calculate¹³C chemical shifts for all 75 PCDD.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 760–761, April, 1994.     

13C NMR spectra of 9-methylcarbazoles and electron conductivity of the carbazole ring

The effect of substituents in the ring of 9-methylcarbazoles on the ¹³C NMR chemical shifts was determined. Correlation relationships between the inductive and resonance constants of the substituents and the chemical shifts were found. The transmission properties of the carbazole ring with respect to the electronic effects of substituents in the 3 position were evaluated on the basis of the results obtained. Nonadditivity of the effects of the substituents on the NMR chemical shifts within the limits of one phenyl ring of carbazole relative to monosubstituted benzenes was observed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 204–209, February, 1984.     

13C NMR spectroscopic data for glutinol and derivatives

The ¹³C NMR chemical shifts of the triterpenes glutinol, glutinone and acetylglutinol were measured and analysed.     

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.     

13C NMR studies on trifluoroacetyl derivatives of 2-acetamido-2-deoxyhexoses

The effect of trifluoroacetylation on the ¹³C chemical shifts of 2-acetamido-2-deoxyhexoses was examined. Studies of the 2-acetamido derivatives of glucose, galactose and mannose established that no regular trend in the ¹³C shifts occurred on trifluoroacetylation. This was in marked contrast to the results obtained for the ¹H chemical shifts.     

Solid‐state 13C, 15N and 29Si NMR characterization of block copolymers with CO2 capture properties

Natural abundance solid‐state multinuclear (¹³C, ¹⁵N and ²⁹Si) cross‐polarization magic‐angle‐spinning NMR was used to study structures of three block copolymers based on polyamide and dimethylsiloxane and two polyamides, one of which including ferrocene in its structure. Assignment of most of the resonance lines in ¹³C, ¹⁵N and ²⁹Si cross‐polarization magic‐angle‐spinning NMR spectra were suggested. A comparative analysis of ¹³C isotropic chemical shifts of polyamides with and without ferrocene has revealed a systematic shift towards higher δ ‐values (de‐shielding) explained as the incorporation of paramagnetic ferrocene into the polyamide backbone. In addition, the ¹³C NMR resonance lines for ferrocene‐based polyamide were significantly broadened, because of paramagnetic effects from ferrocene incorporated in the structure of this polyamide polymer. Single resonance lines with chemical shifts ranging from 88.1 to 91.5 ppm were observed for ¹⁵N sites in all of studied polyamide samples. ²⁹Si chemical shifts were found to be around ?22.4 ppm in polydimethylsiloxane samples that falls in the range of chemical shifts for alkylsiloxane compounds. The CO₂ capture performance of polyamide‐dimethylsiloxane‐based block copolymers was measured as a function of temperature and pressure. The data revealed that these polymeric materials have potential to uptake CO₂ (up to 9.6 cm³ g^?1) at ambient pressures and in the temperature interval 30–40 °C. Copyright © 2016 John Wiley & Sons, Ltd.     

13C NMR spectroscopic studies of the behaviors of carbonyl compounds in various solutions

¹³C NMR spectroscopic studies were performed for carbonyl compounds having a hydroxyl group, a carboalkoxy group, an acetoxy group, or a carboxyl group in various solvents with different polarities for observation of their behaviors of ¹³C NMR chemical shifts of carbonyl carbons in solutions. It was found that the chemical shifts of the carbonyl carbons in ¹³C NMR have good correlation with the empirical parameter for solvent polarities, E_T^N, depending on the structures. Inter- or intramolecular hydrogen bonding and dipolar-dipolar interactions appear to play a key role in this observation.     

13C NMR spectral study of polyacetoxyxanthones. IV—13C NMR spectroscopy of substituted xanthones

The ¹³C NMR chemical shifts of nine acetoxyxanthones are reported and identified. The acetoxy substituent effects have been evaluated and the corresponding shift increments proposed.     

13C NMR spectra of protonated S-methylquinolines

The signals in the¹³C NMR spectra of protonated 2-, 3-, 4-, 5-, 6-, and 8-S-methylquinolines in solution in 6 N DCl were assigned. The changes in the¹³C chemical shifts relative to the neutral molecules were compared with the results of calculations within the CNDO/2 approximation. It is shown that when the molecules are protonated, the shift of the¹³C signals is due to changes in the charges and the paramagnetic components of shielding of the nuclei.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 663–665, May, 1980.     

13C NMR spectra of polycyclic diaziridines

A significant difference between experimental¹³C NMR chemical shifts and those predicted from the¹³C NMR/IR databank was found for bi- and tricyclic diaziridines. Quantum chemical (AMI) and molecular-mechanical (MMX) calculations showed that the relative chemical shift of the nodal C atom is dependent mainly on deformations of the C-C-C valence angle at this atom.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2496–2499, November, 1991.