1H and13C NMR spectra of 1,5-disubstituted 1,3,4-oxadiazoles

The¹H and¹³C NMR spectra of 2, 5-disubstituted 1,3,4-oxadiazoles with aliphatic, aromatic, and hetero-aromatic substituents have been described and interpreted. The electronic effect of the 1,3,4-oxadiazole group as a benzene ring substituent was evaluated using¹³C NMR spectroscopy.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 834–842, June, 1994. Original article submitted April 8, 1994.     

The investigation of the electronic effects of polyfluoro-aryl group by means of nmr spectroscopy

The relationship between NMR ¹⁵N, ¹⁷O, ³¹P, ⁷⁷Se, ¹³C spectral parameters and electronic structure of number of polyfluoroaromatic compounds has been discussed. The increase of the nuclei shielding has been found in all classes of investigated polyfluorinated compounds in respect to the corresponding hydrocarbon analogues. That effect has been discussed in terms of decrease of the conjugation between the unshared electron density of heteroatoms and the π-system of polyfluorinated benzene ring. The conductivity of substituent electronic effects on the π-system of the polyfluoroaryl group by the heteroatom has been estimated from NMR ¹³C data. The sensitivity of nuclei shielding towards interamolecular electronic effects has been noticed to increase from oxygen to selenium and the analysis of the influence of the intramolecular electronic effects on the ¹⁷O and ⁷⁷Se shifts has been given. The influence of the substituents either in pentafluorophenyl ring or adjacent to heteroatom have been shown to correspond those in the hydrocarbon analogues.The conclusion about the influence of polyfluoroaryl group on the character of bonds between different atoms in functional group has been made from the NMR ¹⁷O and ¹⁵N data for aromatic nitro-derivatives. Polyfluorophenyl group in respect to phenyl one deshields the oxygen atom and shields the nitrogen atom. The same effect of pentafluorophenyl group has been observed by other spectral methods.The different screening of ¹⁷O, ¹⁵N, ³¹P and ⁷⁷Se nuclei due to the action of substituents adjacent to the element and variation of the coordination number of heteroatom have been used to the solvation of a number of problems in chemistry of the heteroanalogues of carbenium ions and the detail investigation of the mechanism of electrophylic substitution in the field of polyfluoroaromatic compounds.     

Carbon-13 nuclear magnetic resonance spectra of some methyl and phenyl substituted 2H-azirines

Carbon-13 n.m.r. spectra have been obtained for some methyl and phenyl substituted 2H-azirines. The higher field resonance of C-2 than that of the corresponding aziridine carbon is interpreted in terms of ring strain. Substituent effects on the chemical shifts of the azirine ring carbons are discussed. A set of additivity parameters for the methyl and phenyl groups are obtained which can be used for the calculation of the chemical shifts of the azirine ring carbons. The substituent effect of an azirine ring on the chemical shift of benzene is also discussed in comparison with those of some other substituents. A high degree of s character (48.5%) in the exocyclic orbital of C-3 is indicated by a large J(¹³C-3,H) value (242.5 Hz).     

Characterization of 2‐aryl‐1,3,4‐oxadiazoles by 15N and 13C NMR spectroscopy

¹⁵N NMR chemical shifts of 2‐aryl‐1,3,4‐oxadiazoles were assigned on the basis of the ¹H–¹⁵N HMBC experiment. Chemical shifts of the nitrogen and carbon atoms in the oxadiazole ring correlate with the Hammett σ‐constants of substituents in the aryl ring (r² ≥ 0.966 for N atoms). ¹⁵N NMR data are a suitable and sensitive means for characterizing long‐range electronic substituent effects. Additionally, ¹³C NMR data for these compounds are presented. Copyright © 2003 John Wiley & Sons, Ltd.     

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 spectra of N-substituted carbazoles. Transmission of the electronic effects of substituents through the nitrogen atom to the carbazole ring

The effect of substituents attached to the nitrogen atom on the ¹³C NMR chemical shifts was determined for a series of 9-substituted carbazoles. Correlation relationships between the inductive and resonance constants of the substituents and the chemical shifts of the carbon atoms were obtained. It was shown that carbazole derivatives are similar to anilines with respect to the conductivity of electronic effects through the nitrogen atom to the carbazole ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1184–1188, September, 1986.The authors thank N. V. Moskalev for providing them with a sample of carbazole Im.     

Use of 13C NMR Spectroscopy to Establish the Structure of 6(7)-R-Quinoxaline N,N′-Dioxides

The effect of substituents in position 6 on the positions of the signals of the carbon atoms in the ¹³C NMR spectra of substituted 1,2,3,4-tetrahydro-5,10-phenazine N,N′-dioxides has been analyzed, increments of substituents have been found, and a scheme has been proposed for the calculation of the chemical shifts of carbon atoms in the ¹³C NMR spectra of 6(7)-R-quinoxaline N,N′-dioxides. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, 1076–1080, July, 2005.     

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.     

1H and13C NMR spectra of 2-substituted 5-nitrofurans and conformation of chemotherapeutic preparations of the 5-nitrofuran series

The¹H and¹³NMR spectra of t-nitrofuran and 17 2-substituted 5-nitrofurans were investigated. The Δ¹H and Δ¹³C substituent increments [Δ = δ(2-X-5-nitrofuran) δ(5-nitrofuran)] in the spectra of these compounds were analyzed by comparison with the analogous 5-methylfuran and furan derivatives, and the change in the sensitivity of the chemical shifts of the ring protons and the carbon atoms to the effects of substituents X as a function of the electronic character of substituent R was also analyzed. The chemical shifts and the spin-spin coupling constants were used to determine the preferred orientation of the substituents relative to the furan ring. It was found that medicinal preparations of the 5-nitrofuran series (5-nitrofurfurylidenehydrazones) exist in the form of s-trans conformers in solutions in dimethyl sulfoxide and water, whereas furagin has primarily the structure of the E s-trans form. Translated from Khimiya Geterotsiklichesklkh Soedinenii, No. 2, pp. 167–176, February, 1980. The authors thank N. O. Saldabol, M. A. Trushule, and K. K. Venter for providing us with samples of the compounds, the synthesis of which has been described in the literature.     

Conformational mobility of the six-membered ring in 5-oxo-1,3-cyclohexadiene and its derivatives

Molecular mechanics and MNDO calculations showed that the six-membered ring in the molecule of 5-oxo-1,3-cyclohexadiene possesses high conformational mobility. The transition from a planar equilibrium conformation to a distorted sofa conformation in which the C(sp²)-C(=O)-C(sp³)-C(sp²) torsion angle is equal to ±30° increases the energy of the molecule by less than 1 kcal mol^–1. The influence of steric (R = Me, Et, Prⁱ, Bu^t) and electronic (R = NH₂, NO₂) effects of substituents R on the equilibrium conformation and mobility of the carbocycle has been analyzed. Both types of substituents at unsaturated C atoms do not change the equlibrium conformation or flexibility of the six-membered ring. Substituents at saturated C atoms cause the transition of the carbocycle to the distorted sofa conformation and significantly restrict its mobility. The electronic structures of 5-oxo-1,3-cyclohexadiene and its amino and nitro derivatives have been analyzed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 849–854, May, 1995.     

Structures of polychlorinated naphthalenes and oxynaphthalenes and their13C NMR chemical shifts

The increment scheme for calculating chemical shifts of polysubstituted naphthalenes is based on 1- and 2-substituted heterosubgraphs which describe the main part of the substituent effect. The influence of several substituents on¹³C NMR chemical shifts have been described by two-particle increments corresponding to 1,2- and 2,3-ortho-disubstituted heterosubgraphs (the steric interaction of substituents in the same ring) and also to 1,4-conjugation of the substituents. Conjugation of two benzene rings required the introduction of a two-particle 1,8-heterosubgraph to the increment system. The systems of two-particle increments were obtained for polychlorinated naphthalenes, oxynaphthalenes, and polychlorinated oxynaphthalenes. Predicted¹³C NMR spectra of polychlorinated naphthalenes not included in the increment analysis proved to be in good agreement with independent measurements.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp.625–628, April, 1994.     

Substituent cross-interaction effects on the electronic character of the C=N bridging group in substituted benzylidene anilines--models for molecular cores of mesogenic compounds. A 13C NMR study and comparison with theoretical results

13C NMR chemical shifts delta(C)(C=N) were measured in CDCl3 for a wide set of mesogenic molecule model compounds, viz. the substituted benzylidene anilines p-X-C6H4CH=NC6H4-p-Y (X = NO2, CN, CF3, F, Cl, H, Me, MeO, or NMe2; Y = NO2, CN, F, Cl, H, Me, MeO, or NMe2). The substituent dependence of delta(C)(C=N) was used as a tool to study electronic substituent effects on the azomethine unit. The benzylidene substituents X have a reverse effect on delta(C)(C=N): electron-withdrawing substituents cause shielding, while electron-donating ones behave oppositely, the inductive effects clearly predominating over the resonance effects. In contrast, the aniline substituents Y exert normal effects: electron-withdrawing substituents cause deshielding, while electron-donating ones cause shielding of the C=N carbon, the strengths of the inductive and resonance effects being closely similar. Additionally, the presence of a specific cross-interaction between X and Y could be verified. The electronic effects of the neighboring aromatic ring substituents systematically modify the sensitivity of the C=N group to the electronic effects of the benzylidene or aniline ring substituents. Electron-withdrawing substituents on the aniline ring decrease the sensitivity of delta(C)(C=N) to the substitution on the benzylidine ring, while electron-donating substituents have the opposite effect. In contrast, electron-withdrawing substituents on the benzylidene ring increase the sensitivity of delta(C)(C=N) to the substituent on the aniline ring, while electron-donating substituents act in the opposite way. These results can be rationalized in terms of the substituent-sensitive balance of the electron delocalization (mesomeric effects). The present NMR characteristics are discussed as regards the computational literature data. Valuable information has been obtained on the effects of the substituents on the molecular core of the mesogenic model compounds.     

Multinuclear NMR and vibrational spectroscopy studies of the substituent effects in benzensulphonamide inhibitors of the enzyme carbonic anhydrase

Substituent effects on the electronic structure of sixteen biologically active benzensulphonamide derivatives were investigated by means of ¹⁵N, ¹³C, ¹H NMR, and IR spectroscopy, as well as by quantum chemical calculations. Good correlations were found between the spectroscopic data and both substituent constant and computed electronic charges. On this basis the substituent effects are interpreted in terms of electronic charge perturbation, which is linearly transmitted from the substituent to the biofunctional −SO₂NH₂ group. The resonance nature of the substituent seems most important in determining the ¹⁵N chemical shifts, which follow a “reverse” trend; i.e., electron-donor substituents induce downfield ¹⁵N shifts.     

Etude en Résonance Magnétique Nucléaire du Carbone-13 de N-Aryl Pyrazolines-2 Diversement Substituées. Effets de Substituant et Etude Conformationnelle

The ¹³C chemical shifts of 1-phenyl-2-pyrazoline and 25 N-nitrophenyl-2-pyrazolines, with different substituents on the heterocyclic ring, have been assigned. These values are discussed as a function of the steric and electronic nature of the various substituents. The steric effects produced conformational modifications, both in the nitrophenyl and 2-pyrazoline moieties, which explain some of the chemical shifts.     

Anticancer,DNA cleavage,and antimicrobial activity studies of some new Schiff-base titanium(IV) complexes

Two Ti(IV) complexes have been synthesized with biologically active ligands. These ligands and their functional groups were carefully designed and selected from well-known anticancer drugs because of substituents on the aromatic ring. The ligands were prepared by condensation of a mixture of phenylenediamine and the appropriate aldehyde, vanillin, and 3,4-dimethoxybenzaldehyde. The structures of ligands and complexes have been confirmed by spectroscopic data, i.e., IR, ¹H NMR, ¹³C NMR, electronic spectra, elemental (C, H, and N) analyses, magnetic and conductance measurements. Anticancer, DNA, and antibacterial activities are reported. Some compounds showed promising activity against Hela and PC3 cells.     

Carbon-13 NMR investigation of 2,5-diaryl-1,4-dithiins

The ¹³C NMR spectra of eight 2,5-diaryl-1,4-dithiins were recorded and signals were assigned. A linear correlation was observed between the electronegativity of the substituent groups on C-10,10′ and the chemical shifts of C-10,10′ after applying corrections for the magnetic anisotropic effect of the substituents. A Hammett correlation was found between the ¹³C chemical shifts of C-3,6 and C-7,7′ and the σ_p⁺ parameter associated with the substituents on C-10,10′. Extended electronic interaction between the π system of the aryl group and the π system of the dithiin ring was suggested by the observance of an alternating behavior in the magnitude of the substituent effects on the ¹³C shifts of C-2,5 and C-3,6. An alternating effect was also noted in the magnitude of the long-range ¹³C? F coupling constants for these same carbon signals in 2,5-(10,10′-difluoro)diphenyl-1,4-dithiin.     

A direct hydrogen-1, carbon-13, and nitrogen-15 NMR study of lutetium(III)-isothiocyanate complexation in aqueous solvent mixtures

A direct, low-temperature hydrogen-1, carbon-13, and nitrogen-15 nuclear magnetic resonance study of lutetium(III)-isothiocyanate complex formation in aqueous solvent mixtures has been completed. At –100°C to –120°C in water-acetone-Freon mixtures, ligand exchange is slowed sufficiently to permit the observation of separate¹H,¹³C, and¹⁵N NMR signals for coordinated and free water and isothiocyanate ions. In the¹³C and¹⁵N spectra of NCS^–, resonance signals for five complexes are observed over the range of concentrations studied. The¹³C chemical shifts of complexed NCS^– varied from –0.5 ppm to –3 ppm from that of free anion. For the same complexes, the¹⁵N chemical shifts from free anion were about –11 ppm to –15 ppm. The magnitude and sign of the¹⁵N chemical shifts identified the nitrogen atom as the binding site in NCS^–. The concentration dependence of the¹³C and¹⁵N signal areas, and estimates of the fraction of anion bound at each NCS^–:Lu³⁺ mole ratio, were consistent with the formation of [(H₂O)₅Lu(NCS)]²⁺ through [(H₂O)Lu(NCS)₅]^2–. Although proton and/or ligand exchange and the resulting bulk-coordinated signal overlap prevented accurate hydration number measurements, a good qualitative correlation of the water¹H NMR spectral results with those of¹³C and¹⁵N was possible.     

13C and 1H chemical shifts in 2-benzylidene[3]ferrocenophane-1,3-diones. Elucidation of the substituent dependence of carbonyl chemical shifts in different carbonyl derivatives

The ¹³C and ¹H chemical shifts of the ferrocene moiety, as well as the carbonyl carbons and styrene moiety, of substituted 2-benzylidene[3]ferrocenophane-1,3-diones have been assigned. Correlations of ¹³C substituent chemical shifts of both carbonyl carbons with the Hammett constants have been found, and the effect of the transmission of substituent effects on these chemical shifts through the styrene moiety is discussed. An explanation is given for the different sensitivities of the carbonyl carbon chemical shifts to the electronic effect of substituents in mono- and dicarbonyl derivatives.     

Substituent effects in the 13C NMR chemical shifts of para-(para-substituted benzylidene amino)benzonitrile and para-(ortho-substituted benzylidene amino)benzonitrile

¹³C NMR chemical shifts were measured in CDCl₃ for two series of substituted benzylidene anilines. The substituted benzylidene anilines p-X-C₆H₄CH=NC₆H₄-p-CN p-X-C₆H₄CH=NC₆H₄-o-CN (X = NO₂, F, Cl, Br, H, Me, MeO, NMe₂). The substituent dependence of δC(C=N) was used as a tool to study electronic substituent effects on the azomethine unit. The benzylidene substituents X have a reverse effect on δC(C=N): electron-withdrawing substituents cause shielding, while electrondonating ones do the reverse, the resonance effects clearly predominating over the inductive effects. Additionally, the presence of a specific cross-interaction between X and C=N could be verified. The electronic effects of the neighboring aromatic ring substituents systematically modify the sensitivity of the C=N group to the electronic effects of the benzylidene substituents. These results can be rationalized in terms of the substituent-sensitive balance of the electron delocalization (mesomeric effects).     

Carbon-13 NMR studies of 1-aryl-3-phenyl-2-thioxo-4-imidazolidinones. Conformational isomerism and substituent effects

Characteristic ^13C chemical shift ranges and substituent shifts of heterocyclic ring carbon atoms have been identified for a number of 1-aryl-3-phenyl-2-thioxo-4-imidazolidinones. ¹³CNMR spectra may be used to detect slow internal rotation about the aryl C? N-1 bond in compounds with diastereomeric rotational isomers; many corresponding carbon atoms in the rotamers have distinctly different chemical shifts. The δ-effects originating from aryl ortho substituents are both electronic and steric in origin.