Direct13C-13C spin-spin coupling constants for the triple bond in activated acetylenes

Conclusions ¹³C-¹³C SSCC values across the triple bond in activated acetylenes are determined primarily by the -electronic properties of substituents. The enhanced sensitivity of¹J_cc in acetylene derivatives to substituent effects also asserts their possible utility in estimating the electronegative properties of substituents.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1287–1292, June, 1988.     

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.     

Study of the stereochemistry of N-H and N-vinyl-4,5,7-trimethyi-4,5,6,7-tetrahydropyrrolo[3,2-c]pyridines and their nitro derivatives by the method of 1H and 13C NMR

The configurations and conformational features of N-H and N-vinyl-4,5,7-trimethyl-4,5,6,7-tetrahydropyrrolo[3,2-c]pyridines and their nitro derivatives were established by the method of ¹H and ¹³C NMR spectroscopy. It was shown that the conformational uniformity of the piperideine ring in the compounds studied is strongly dependent on the character of the substituents in the pyrrole ring. A method for the determination of the orientation of the substituent at the -position to the nitrogen atom of the piperideine ring, according to the direct ¹J_CH SSCC, was proposed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 75–81, January, 1993.     

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 NMR spectra of 8-mercaptoquinoline and 8-hydroxyquinoline

The signals in the¹³C NMR spectra of quinoline and its 8-substituted derivatives (SH, SCH₃, OH, OCH₃, NH₂, I, and CH₃), 8,8-diquinolyl disulfide, the 8-hydroxy-N-methylquinolinium ion, and the protonated and anionic forms of 8-hydroxy- and 8-mercaptoquinoline were assigned. The increments of the substituents in the neutral forms of these compounds correlate satisfactorily with those in substituted benzenes and the Swain-Lupton parameters (r = 0.94–0.99). The differences in the ortho increments of the substituents are due to a change in the electron densities on the carbon atoms and also to steric hindrance. The effect of an intramolecular hydrogen bond on the¹³C chemical shift of the quinoline ring of 8-hydroxy- and 8-mercaptoquinoline was examined. The¹³C chemical shifts correlate satisfactorily with the total charges (q) on the carbon atoms in the neutral forms of these compounds. A similar correlation is satisfied to a lesser extent for the protonated and anionic forms because of a change in the bond orders.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 657–662, May, 1980.     

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.     

Study of three-dimensional structures of benzoylpyridine oximes and their ethers by 1H and 13C NMR spectroscopy

The ¹H and ¹³C NMR spectra of the E and Z isomers of 2-, 3-, and 4-benzoylpyridine oximes and their ethers were analyzed thoroughly, and the ¹H-¹³C spin-spin coupling constants (SSCC) were determined. It was established that the magnitude of the effect for the quaternary carbon atoms in the E and Z isomers depends on the site of substitution in the pyridine ring. It was assumed that the intermolecular hydrogen bond is stronger in the E form than in the Z form. The existence of the Z isomer of 2-benzoylpyridine oxime in deuterochloroform with an intramolecular hydrogen bond was proved.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 203–208, February, 1990.     

Substituenteneffekte in den13C-NMR-Spektren von diastereomeren Chalkondihalogeniden, 10. Mitt.: Erste Synthese und Konfigurationsbestimmung vonthreo-Chalkonbromhydrinen

Summary The first synthesis ofthreo chalcone bromohydrins was realized by reaction oftrans chalcone epoxides with SnBr₄ in molar ratios from 1:1 to 2:1. The compounds were obtained in high yields and isomeric purity. Their configuration was determined asthreo by different methods based on¹³C-NMR shifts of C- and C- atoms.

     

Spin-spin coupling constants of 13C-1H and 1H- 1H in 4-substituted pyridines

The spin-spin coupling constants (SSCC) of ¹³C-¹H and ¹H-¹H in 4-substituted pyridines, C₅H₄NX [X=,CN, COCH₃, COOCH₃, N(CH₃)₂, NO₂, OCH₃, Cl, Br], were investigated. To determine the constants, the proton-coupled NMR spectra of ¹³C and ¹³C-satellites in the PMR spectra of the compounds, recorded for monomolecular solutions of 4-substituted pyridines in DMSO-D₆, were analyzed. The interrelationship of the SSCC of ¹³C-¹H and ¹H-¹H in 4-substituted pyridines with the analogous constants in monosubstittued benzenes were obtained. The correlations of the constants with the F- and R-parameters of the substituents are discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 948–952, July, 1984.     

<Superscript>13</Superscript>C-<Superscript>13</Superscript>C spin-spin coupling constants in structural studies: XXXIX. Nonempirical calculations of heteroaromatic oximes

The results of high-level nonempirical quantum-chemical calculations of ¹³C-¹³C coupling constants in twelve heteroaromatic ketone oximes are well consistent with the available experimental data. In all the examined compounds, the effect of the unshared electron pair on the oxime nitrogen atom on J _CC strongly predominates over conformational and electronic effects, which makes it possible to unambiguously assign J _CC values to different configurations.     

<Superscript>13</Superscript>C-<Superscript>13</Superscript>C spin-spin coupling constants in structural studies: XL. Conformational analysis of <Emphasis Type="Italic">N</Emphasis>-vinylpyrroles

Conformational analysis of ten N-vinylpyrroles was performed on the basis of experimental ¹³C-¹H and ¹³C-¹³C coupling constants and those calculated by high-level quantum-chemical methods, and principal relations between J _CC and J _CH values and stereochemical structure of these compounds were revealed.     

Conformation of monobenzyl ethers of piperidyl-containing acetylenic glycols,according to13C NMR spectroscopic data

In the¹³C NMR spectra of individual ()- and ()-epimers (through the C₄ carbon atom of the six-membered ring) of monobenzyl ethers of piperidyl-containing acetylenic glycols, it has been found that the chemical shifts of the epimers differ by as much as 3 ppm for the C₂, C₄, and C₆ carbon atoms. The most probable conformations of the epimers are suggested, including intramolecular hydrogen bonds between the proton of the OH group and the unshared electron pair of the nitrogen.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2780–2785, December, 1991.     

Synthesis of 13c-labelled [s]-proline and its conformational analysis by nuclear magnetic resonance

In order to analyze completely the ring conformation of [S]-Proline (l-thiazolidine-4-carboxylic acid) this compound has been synthesized with its C_δ atom enriched at 90% in ¹³C. The ¹H-¹H, ¹³C-¹H, ¹³C-¹³C vicinal coupling constants measured at several pH values describe well the geometry of the thiazolidine ring. The results suggest that the ring has an average planar conformation only in a narrow range of pH close to the pK of the amine group. Above and below this pH the ring tends to adopt preferentially the S_γendo and S_γexo puckered conformations respectively. It is concluded that a good correlation exists between the value of the dihedral angle ø and the character S_γendo or S_γexo of the ring.     

Synthesis and nmr analysis of cyclo-[85% 13C-asp]-pro: 13C-13C vicinal coupling constants and conformation

The dipeptide cyclo(Asp-Pro) where the aspartic acid residue was 85% ¹³C enriched, was synthesized with the aim of analyzing its conformation in solution by using ¹C-¹H, ¹³H-¹H and ¹³C-¹³C coupling constant parameters. The values of these couplings agree well with each other and show that the side chain of the aspartic acid residue adopts privileged conformations the proportions of which vary somewhat with pH, and more weakly, with a change in solvent. The ¹³C-¹³C interresidue coupling constants ³J_Cl'–_C2^β and ³J_Cl'–_C2^γ obtained after long accumulation of the signals of unenriched carbons, have different values; they show puckering in the pyrrolidine ring similar to that found in cyclo(Leu-Pro) in the solid state. It was concluded that ¹³C-¹³C coupling constants represent an excellent means of determining the side chain conformation (whenever the incorporation of an enriched amino acid into the peptide is possible) that will find applications particularly in the case of peptides with complicated proton spectra.     

Specific C-H...N intramolecular interaction in 1-vinyl-2-cyanoethylthiobenzimidazole with the formation of a nine-membered intramolecular ring,according to1H and13C NMR data

In the¹H NMR spectrum of 1-vinyl-2-cyanoethylthiobenzimidazole, an abnormal downfield shift has been found in the signal of the -hydrogen atom of the vinyl group, and also an increase in the corresponding direct¹³C-¹H spin-spin coupling constant, in comparison with other 2-substituted benzimidazoles. This indicates a specific C-H...N intramolecular interaction in this molecule between the -hydrogen atom and the cyano nitrogen atom, forming a nine-membered intramolecular ring.Translated from Translated from Izvestiya Akademii Nauk SSSR No. 10, pp. 2285–2288, October, 1991.     

Heteroorganic derivatives of furan. 65. Effect of substituents on shielding of 1H, 13C,and 29Si and 29Si-13C spin-spin coupling constants in NMR spectra of 2-substituted furans and 5-trimethylsilylfurans

The results of an investigation of 2-substituted furans and 5-trimethylsilylfurans by NMR spectroscopy and the CNDO/2 method showed that the chemical shifts of the different nuclei do not correlate sufficiently clearly with the calculated charges because of an additional change in the electron density under the influence of a -d interaction. The ¹³C-²⁹Si direct spin-spin coupling constants (SSCC) are less sensitive to this interaction, since they depend primarily on the inductive effects of the substituents.See [1] for Communication 64.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 588–596, May, 1990.     

1H, 1 3C,and 1 5N Chemical shifts and 1H-1 5N and 1 3C-1 5N heteronuclear spin-spin coupling constants in the NMR spectra of 5-substituted furfural oximes

The ¹H, ¹³C, and ¹⁵N NMR spectra of ¹⁵N-enriched 5-substituted furfural oximes were investigated. It was shown that the chemical shifts of the ring atoms and the oxime group correlate satisfactorily with the F and R substituent constants, whereas their sensitivity to the effect of the substituents is lower than in monosubstituted furan derivatives. The constants of spin-spin coupling between the ring protons and the oxime group were determined. An analysis of the ¹H-¹H spin-spin coupling constants (SSCC) on the basis of their stereospecificity indicates that the E isomers have primarily an s-trans conformation in polar dimethyl sulfoxide, whereas the Z isomers, on the other hand, have an s-cis conformation. The signs of the direct and geminal ¹³C-¹⁵N SSCC were determined for 5-trimethylsilylfurfural oxime.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1172–1177, September, 1985.The authors thank N. O. Saldabol, L. M. Ignatovich, and N. P. Erchak for providing us with the investigated compounds.     

Stereochemistry of nitrogen heterocycles. 69. 13C NMR spectra of stereoisomeric 10-methyl-5-oxygen-substituted trans-decahydroquinolines

The ¹³C NMR spectra of 5-keto- and 5a- and 5e-hydroxy-10-methyl- and 1,10-dimethyltrans-decahydroquinolines have been recorded and interpreted. The increments of the oxo and hydroxy groups in the 10-methyldecahydroquinoline and the isostructural 10-methyldecaline systems were compared. The difference between the increments of azacyclic and the carbocyclic systems appears- at the -positions relative to the electronegative substituents (C₍₇₎ and C₍₉₎) and at the antiperiplanar -positions relative to nitrogen (C₍₅₎ and C₍₇₎). The increments of the oxo and the equatorial hydroxy groups in the aza ring are more shielded than in the carbon ring (at C₍₇₎, 2 ppm; at C_(g), 1 ppm), while the increments of the axial hydroxy group are more deshielded (at C₍₅₎, 1.5–2.0 ppm; at C₍₉₎, 1.0–1.5 ppm). The more the respective carbon atoms of the heterocycle are hydrogenated, the stronger are the deshielding -effect and the shielding -effect of the methyl group on nitrogen.For Communication 68, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 60–65, January, 1990.     

Kernresonanzuntersuchungen am 1.10-Phenanthrolin und seinen Komplexverbindungen—IV: 13C-Resonanzen des freien und protonierten 1.10-Phenanthrolins

The ¹³C chemical shifts of free and protonated 1,10-phenanthroline have been measured and interpreted by means of π- and (σ + π)-MO-electron calculations as described in Parts I¹ and III.² For the protonated molecule a high field ¹³C shift of the C-atom adjacent to the N-atom is characteristic; this effect is explained in terms of a decrease of the N–C overlap population. For the mono- and diprotonated 1,10-phenanthroline the best correlation with the experimental shift values was obtained by assuming a small formal charge on the nitrogen atom (Δ = 0·0 to 0·3).     

<Superscript>13</Superscript>C-<Superscript>13</Superscript>C spin-spin coupling constants in structural studies: XLIV. Carbonyl-containing oximes

¹³C-¹³C spin-spin coupling constants in carbonyl-containing oximes were calculated in terms of the second-order polarization propagator approximation (SOPPA) with account taken of the results of theoretical conformational analysis. Stable conformations of all carbonyl-containing oximes were found to have s-trans orientation of the carbonyl group in the E and Z isomers. The corresponding ¹³C-¹³C coupling constants showed a characteristic dependence upon internal rotation of the carbonyl-containing substituent, which may be used to determine predominant rotational conformations of these compounds. A relation between orientation of the C=O bond and ¹³C-¹³C coupling constants for the adjacent bonds in oximes was revealed; it may be attributed to hyperconjugation between the corresponding carbon-carbon bond and antibonding orbital of the C=O bond.