NMR study of conjugation effects 15.13C-13C spin-spin coupling constants in phenyl alkyl ether

Conclusions ¹³C-¹³C SSCC were measured for a series of phenyl alkyl ethers. The values through the bond between C² and C³ in mono substituted benzenes most clearly reflect the -electron interaction of the aromatic ring with the substituent, provided the latter contains no atoms from a period of the periodic table higher than the second.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya.No. 1, pp. 113–119, January, 1982.The authors thank N. M. Sergeev for useful discussions while the work was in progress, and V. N. Khlopkov for technical assistance in setting up the experiments.     

Direct13C-13C spin-spin coupling constants of olefinic carbons in vinyl ethers

Conclusions In alkyl vinyl ethers, the values of¹J (¹³C=¹³C) SSCC increase with increasing effective volume of the alkyl group, opposite to the change in the corresponding constants in the series of alkyl phenyl ethers.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2249–2252, October, 1982.     

Calculation of the torsional angles in alkyl vinyl ethers from the direct13C-1H spin-spin interaction constants

It is shown that the differences in the direct¹³C-¹H SSIC of the C atom of the vinyl groups in alkyl vinyl ethers depend on the value of the torsional angle about the C bond. This dependence is used to make quantitative estimates of the torsional angles in alkyl vinyl ethers with alkyl substituents ranging from CH₃ to t-C₄H₉ Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 390–393, February, 1991.The authors are grateful to S. V. Kirpichenko for providing the triethylvinylthiosilane, synthesized as described in [11].     

Direct 13C-13C spin-spin coupling constants in the vinyl group of N-vinylazoles

The unshared electron pair of the dicoordinated nitrogen atom introduces a stereospecific contribution to the ¹³C-¹³C spin-spin coupling constant (SSCC) in the vinyl group of a series of N-vinylazoles, the value of which depends on the energetics of the unshared pair.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 197–200, February, 1989.     

13C-13C Coupling Constants in Structural Studies: XXXIII. Stereochemical Study of the Pyranose Ring

¹³C-¹³C coupling constants for all aldopyranoses of the D-series were calculated in terms of the self-consistent finite perturbation theory. General relations holding in the stereochemical behavior of the ¹³C-¹³C coupling constants for the pyranose ring were found. The results obtained make it possible to perform conformational analysis and assign configuration of the anomeric center in molecules of carbohydrates and products of their metabolism, containing a pyranose fragment.     

13C-13C Spin-Spin Coupling Constants in Structural Studies: XXXVI. Stereochemical Study of the Septanose Ring

¹³C-¹³C Spin-spin coupling constants of aldoseptanoses of the Dseries were calculated in terms of the self-consistent finite perturbation theory. General relations holding in the stereochemical behavior of the ¹³C-¹³C coupling constants in the septanose ring were determined, which made it possible to perform conformational analysis and assign configuration of the anomeric centers in carbohydrates and products of their metabolism.     

13C-13C spin-spin coupling constants in the spectra of monosubstituted pyridines

The ¹³C- {¹H} NMR spectra of pyridine and a number of monosubstituted pyridines for compounds with the natural percentage of the ¹³C isotope were analyzed. The direct, geminal, and vicinal ¹³C-¹³C spin-spin coupling constants (SSCC) were determined. Linear relationships that link the ¹³C-¹³C SSCC in the spectra of monosubstituted pyridines and benzenes were obtained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1383–1385, October, 1985.     

13C-13C spin-spin coupling constants in six-membered ring azaaromatic compounds

The ¹³C-{¹H} NMR spectra of monomethyl substituted diazines, protonated at the picoline and 2-methylopyrimidine nitrogen atoms, have been analyzed, along with that of pyridine N-oxide and its 2-methyl derivatives protonated at the oxygen atom. Direct and vicinal ¹³C-¹³C spin-spin coupling constants (SSCC) have been measured. It was found that the ¹³C-¹³C SSCC in diazines follow additivity rules which are based on consideration of the number and mutual orientation or distribution of nitrogen atoms in the ring. It has also been demonstrated that increased direct ¹J_CC values involving methyl group carbon atoms in -positions to nitrogen atoms in the aromatic ring are due to effects associated with unshared electron pairs.Translated from Khimiya Geterotsiklieheskikh Soedinenii, No. 9, pp. 1243–1250, September, 1988.     

Interglycosidic 13C-1H coupling constants. An approach to disaccharide conformations.

Interglycosidic ¹³C-¹H coupling constants have been measured for different saccharides by selective 2D-J heteronuclear n.m.r. spectroscopy.     

13C-13C spin-spin coupling constants in structural studies: XLIII. Stereochemical study on functionalized 3-iminopyrrolizines

Three 1-ethylsulfanyl-3-imino-3H-pyrrolizine-2-carboxamides were synthesized by intramolecular cyclization of substituted (2Z)-2-cyano-3-ethylsulfanyl-3-(1H-pyrrol-2-yl)prop-2-enamides. The products were assigned syn configuration at the C=N bond and preferential s-cis orientation of the carbamoyl group on the basis of the experimental ¹³C-¹³C coupling constants and high-level nonempirical quantum-chemical calculations.     

13C-13C Spin-Spin Coupling Constants in Structural Studies: XXXVII. Rotational Conformations of Hydroxy Groups in Pyranose, Furanose, and Septanose Rings

Rotational surfaces for ¹³C-¹³C coupling constants with respect to two dihedral angles at C¹ and C² in model structures of aldopyranoses, aldofuranoses, and aldoseptanoses of the D-series were calculated in terms of the self-consistent finite perturbation theory. Internal rotation of the hydroxy groups exerts an appreciable effect (within 2.5 Hz) on the ¹³C-¹³C coupling constants of all cyclic forms of monosaccharides, which provides the possibility for performing conformational analysis of carbohydrates and their metabolites containing pyranose, furanose, and septanose fragments.     

Evidence of Long-Range 13C-31P Couplings: A 13C NMR Investigation of Some Aryl Esters of Phosphor-Amidochloridic Acid and the Related Compounds

Abstract

In ¹³ NMR study organophosphorus compounds, sign and magnitude of ¹³ C-³¹ P spin-spin couplings has been of great interest to elucidate stereochemistry and electronic state of phosphorus central atom. However, a discussion about the mechanisms of carbon-phosphorus couplings is still complicated specially in the case of long-range couplings that also are not frequently observed. In this study, ¹³ C NMR chemical shifts and coupling constants have been determined for a series of aryl esters of phosphoramidochloridic acid with the general formula: R₂NP(O)(OAr)Cl, in which R = methyl and/or benzyl, Ar = p-tolyl. p-nitrophenyl, and phenyl. Besides usual W-couplings that could be found in these systems, we detected long-range couplings through five and six bonds. It has been shown that, these couplings are highly dependent on substituents on phosphorus nuclei. The data for some related compounds have been also obtained for a comparison.     

Direct13C-1H coupling constants in the vinyl group of 1-vinylpyrazoles

Conclusions The¹³C-¹H direct coupling constants in the vinyl group of 1-vinylpyrazoles are stereo-specific and vary with change in the conformer ratio.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 202–204, January, 1987.     

Establishing the configuration of imine nitrogen compounds: Influence of alkyl groups on13C-13C spin-spin coupling constant in alkyl phenyl ketoximes

Conclusions In a series of alkyl phenyl ketoximes, the constant of spin-spin coupling of the oxime carbon with the -carbon atom of the phenyl group is determined by the inductive effect of the alkyl groups; this makes it possible to identify configurational isomers of similar compounds of imine nitrogen in those cases in which the corresponding carbon-carbon can be measured only in one isomer.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 766–769, April, 1987.     

Elucidation of the Structure of Lignin–Carbohydrate Complexes in Ginkgo CW-DHP by 13C-2H Dual Isotope Tracer

To elucidate the chemical linkages between lignin and carbohydrates in ginkgo cell walls, ¹³C-²H-enriched cell wall-dehydrogenation polymers (CW-DHP) were selectively prepared with cambial tissue from Ginkgo biloba L. by feeding D-glucose-[6-²H₂], coniferin-[α-¹³C], and phenylalanine ammonia-lyase (PAL) inhibitor. The abundant detection of ¹³C and ²H confirmed that D-glucose-[6-²H₂] and coniferin-[α-¹³C] were involved in the normal metabolism of ginkgo cambial cells that had been effectively labelled with dual isotopes. In the ginkgo CW-DHP, ketal and ether linkages were formed between the C-α of lignin side chains and carbohydrates, as revealed by solid state CP/MAS ¹³C-NMR differential spectroscopy. Furthermore, the DMSO/TBAH ionic liquids system was used to fractionate the ball-milled CW-DHP into three lignin-carbohydrate complex (LCC) fractions: glucan–lignin complex (GL), glucomannan–lignin complex (GML), and xylan–lignin complex (XL). The XRD determination indicated that the cellulose type I of the GL was converted into cellulose type II during the separation process. The molecular weight was in the order of Ac-GL > Ac-GML > XL. The ¹³C-NMR and ¹H-NMR differential spectroscopy of ¹³C-²H-enriched GL fraction indicated that lignin was linked with cellulose C-6 by benzyl ether linkages. It was also found that there were benzyl ether linkages between the lignin side chain C-α and glucomannan C-6 in the ¹³C-²H-enriched GML fraction. The formation of ketal linkages between the C-α of lignin and xylan was confirmed in the ¹³C-²H-enriched XL fraction.     

13C-13C Spin-Spin Coupling Constants in Structural Studies: XXXI. Bicyclo[2.1.0]pentane Heteroanalogs

¹³C-¹³C spin-spin coupling constants and orbital hybridization of the bridging bond in bicyclo[2.1.0]pentane heteroanalogs and their unsaturated derivatives were calculated in terms of the self-consistent finite perturbation theory (SCPT INDO). The results showed that the bridging CÄC bond in all the examined compounds has an anomaloulsy low s character.     

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.     

Reducing the computational cost of NMR crystallography of organic powders at natural isotopic abundance with the help of 13C-13C dipolar couplings

Structure determination of functional organic compounds remains a formidable challenge when the sample exists as a powder. Nuclear magnetic resonance crystallography approaches based on the comparison of experimental and Density Functional Theory (DFT)-computed ¹H chemical shifts have already demonstrated great potential for structure determination of organic powders, but limitations still persist. In this study, we discuss the possibility of using ¹³C-¹³C dipolar couplings quantified on powdered theophylline at natural isotopic abundance with the help of dynamic nuclear polarization, to realize a DFT-free, rapid screening of a pool of structures predicted by ab initio random structure search. We show that although ¹³C-¹³C dipolar couplings can identify structures possessing long range structural motifs and unit cell parameters close to those of the true structure, it must be complemented with other data to recover information about the presence and the chemical nature of the supramolecular interactions.     

13C-13C Coupling Constants in Structural Studies: XXXII. Additivity of Spin-Spin Couplings in Sterically Strained Heterocycles

Calculations in terms of the self-consistent finite perturbation theory (SCPT) and analysis of contributions of localized molecular orbitals in terms of the polarization propagator theory (CLOPPA) indicate additivity of ¹³C-¹³C coupling constants in saturated sterically strained heterocycles. Their fused derivatives, especially those containing 3rd Period elements, show considerable deviations of the calculated coupling constants from the additive values.     

Use of13C-13C spin-spin coupling constants for establishing the configuration of 1-alkoxy-1-aminoxyethanes

Conclusions Direct¹³C-¹³C coupling constants were used to establish the configuration of 1-alkoxy-1-aminoxyethanes. The compounds are mixtures of Z and E isomers, of which the E isomers are more stable.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2137–2138, September, 1985.