13C NMR Spectra of cyclic nitrones. 1. 2-substituted 4-methyl- and 4-phenyl-1-hydroxy-5,5-dimethyl-3-imidazoline 3-oxides

The introduction of an N-oxide oxygen atom into azomethines leads to an upfield shift of the signals for the carbon atom of the G=N group in the ¹³C NMR spectra by 30–33 ppm. This is consistent with the increase in the electron density on this atom. The signal of the nitrone carbon atom is observed in the region of 140–147 ppm, depending on the nature of the substituent at the C(₂) atom of the 3-imidazoline 3-oxide ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 247–251, February, 1985.     

NMR spectra of cyclic nitrones. 4. Synthesis and 13C NMR spectra of 4H-imidazole N-oxides and N,N-dioxides

4H-Imidazole 1,3-dioxides and 4H-imidazole 3-oxides were obtained by oxidation of 1-hydroxy-3-imidazoline 3-oxides and 1-hydroxy-3-imidazolines with lead and manganese dioxides or the stable nitroxyl radical, while 4H-imidazole 1-oxides were obtained by thermal decomposition of 1-acetoxy-3-imidazoline 3-oxides. Facile oxidation of the ethyl group in 5-ethyl-4H-imidazole 1,3-dioxide and the formation of 5-acetyl-4H-imidazole 1,3-dioxide and 5-acetyl-4H-imidazole 3-oxide were observed. It is shown that a strictly determined region of chemical shifts of the C(₂), C(₅), and C(₄) atoms is characteristic for each group of 4H-imidazole N-oxides in the ¹³C NMR spectra; this makes it possible to clearly establish the position of the N-oxide oxygen atom.See [1] for Communication 3.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1640–1648, December, 1988.     

Proton-coupled 13C NMR spectra of 2- and 3-substituted pyridines

The proton-coupled ¹³C NMR and PMR spectra of pyridine and the 2- and 3-monosubstituted pyridines NC₅H₄X [where X=CH₃, CN, COCH₃, COOCH₃, N(CH₃)₂, NO₂, OCH₃, Cl, or Br] for one-molar solutions of the compounds in DMSO-D₆, have been analyzed. The signs and values of the ¹³C-¹H HSSCs have been determined. Equations have been obtained connecting the ¹³C-¹H SSCCs in the 2- and 3-substituted pyridines and the monosubstituted benzenes. A satisfactory correlation of ¹JCH with the F and R constants of the substituents has been shown.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1223–1230, September, 1984.     

NMR spectra of cyclic nitrones. 5. 13C NMR spectra of the potential tautomeric systems of amino-, hydroxy-, and mercaptonitrones in the series of 3-imidazoline 3-oxide

The position of the tautomeric equilibrium in amino-, hydroxy, and mercaptonitrones was determined by the ¹³C NMR method for the case of the derivatives of 3-imidazoline-3-oxide. It was shown that the tautomeric equilibrium in the OH and SH derivatives is shifted toward the oxo and thioxo forms (95%). The chemical shifts of the carbon atoms of the nitrone group in the -N-, -O-, and -S-substituted nitrones lie in the region of 137–150 ppm.For Communication 4, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 478–482, April, 1990.     

13C NMR spectra of some 4-substituted protoadamantanes

The ¹³C NMR spectra of some mono- and geminal disubstituted protoadamantanes have been assigned with the aid of shift reagents.     

13C NMR spectra of 3-substituted phlorophenone compounds

The ¹³C NMR spectra of a series of 3-allyl-, 3-prenyl- and 3-benzyl-phlorophenone compounds are reported. Relative substituent effects are discussed.     

The NMR spectra of cyclic nitrones. 3. Effect of protonation and a hydrogen bond on the chemical shifts in the13c NMR spectra of derivatives of 3-imidazoline 3-oxide

The effect of solvents on the¹³C NMR spectra of the cyclic nitrones of 3-imidazoline 3-oxide derivatives was studied. It was shown that in solvents capable of forming hydrogen bonds with the N-oxide group the signal for the nitrone carbon atom is shifted downfield by 1.5–2.5 ppm for solutions in chloroform and 5–9 ppm for solutions in methanol. The size of the shift depends on the substituent at position 1 of the imidazoline ring and decreases with increase in its accepting character. Analogous effects are observed during the formation of an intramolecular hydrogen bond with the oxygen atom of the nitrone group. During protonation of the nitrone group the downfield shift of the signal for the nitrone carbon atom amounts to 30–39 ppm.For Communication 2, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1065–1072, August, 1986.     

Stereochemistry of alkyl 3-substituted 4-halotetrahydro-2-oxo-3-furancarboxylates: 2—1H and 13C NMR spectra

The ¹H NMR parameters of methyl 3-substituted cis-4-halotetrahydro-2-oxo-3-furancarboxylates are reported, with assignments of the ring protons based on solvent-induced changes in the vicinal trans coupling constants, ³J(H-4, H-5). Preferred conformations, ce with a pseudo-equatorial halogen for the cis isomers and ta with a pseudo-axial halogen for the trans isomers, have been suggested on comparison of the magnitudes of J(trans) and J(gem) in both series. The ³J(¹³CH₃, H-4) values measured for methyl cis-4-bromotetrahydro-3-methyl-3-furancarboxylate, methyl trans-4-bromotetrahydro-3-methyl-3-furancarboxylate and trans-3,4-dibromodihydro-3-methyl-2(3H)-furanone have confirmed the stereochemical assignments.     

Carbon-13 NMR spectra of some 4- and 5-substituted pyrimidines

Carbon-13 NMR chemical shifts and carbon-proton coupling constants for nine 4-substituted and six 5-substituted pyrimidines are reported. The carbon chemical shifts are correlated with π-electron densities. Carbon-proton coupling constants fail to correlate with substituent electronegativity.     

Electron structures and 13C NMR spectra of 3-substituted coumarin derivatives

Quantum-chemical calculation of the electron densities on the atoms and the Wiberg indexes in coumarin and 3-amino-3-hydroxy-, and 3-carboxycoumarin molecules within the CNDO/2 approximation was accomplished. The ¹³C NMR spectra of the indicated compounds were recorded. The effect of the nature of the substituent in the pyrone ring on the electron structures of 3-substituted coumarin derivatives was evaluated on the basis of the data obtained. The character and degree of the relationship between the chemical shifts and the electron densities on the carbon atoms were established by means of regression analysis.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1611–1614, December, 1988.     

13C NMR spectra of some 1-, 3- and 4-monosubstituted and disubstituted isoquinolines

Chemical shifts and substituent chemical shift (SCS) effects are reported for 21 monosubstituted iso-quinolines, carrying a halogeno, amino, piperidino or ethoxy group in position 1, 3 or 4. In some cases, assignments of ¹³C resonances were based on the spectra of the corresponding 5-deutero derivatives. For the fluoroisoquinolines some ¹³CF coupling constants are given. The ¹³C NMR spectra of 15 disubstituted isoquinolines were measured; with a few exceptions, mainly the 3,4- and 1,4-disubstituted isoquinolines, the chemical shifts agreed well with those calculated by addition of the SCS effects.     

13C and 15N NMR spectra of 2,3-substituted 2H-azirines

The ¹³C and ¹⁵N NMR spectra of a series of 2,3-substituted 2H-azirines have been studied. The ¹⁵N chemical shift for the nitrogen in the azirine ring is found at much higher field than in acyclic imines with a considerable electronic effect for the substituents on the double bond. Cooperative steric and electronic effects associated with substituents on the unsaturated carbon atom of the ring were found to influence the shielding of the ¹³C and ¹⁵N nuclei. Reaction constants have been calculated for 2-alkyl(aryl)-3-phenylazirines. It has been shown that the azirine ring has a powerful —I effect (when compared with the phenyl ring) that exceeds the analogous value for the cyano group.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1181–1183, September, 1986.     

13C NMR spectra of 7-substituted 8-mercaptoquinolines

The¹³C NMR spectra of 7-substituted [7-CH₃, 2,7-(CH₃)₂, 7-Cl, 7-Br, and 7-SCH₃] 8-mercaptoquinolines and 8-methylmercaptoquinolines were examined. It is shown that the changes in the¹³C chemical shifts of the quinoline ring in the spectra of 7-substituted 8-mercaptoquinolines are in good agreement with the additive contribution of the increments of the substituents, i.e., their conjugation with the ring is not disrupted. The conjugation of the SCH₃ group with the quinoline ring in 7-substituted 8-methylmercaptoquinolines is disrupted as a consequence of steric hindrance, and this leads to a decrease in the increments of this group. The data obtained are compared with the results of a calculation within the CNDO/2 approximation. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 801–805, June, 1980.     

13C NMR spectra of 5-substituted 8-mercaptoquinolines

The increments of the substituents were determined from the ¹³C NMR spectra of 5-substituted quinolines. It is shown that the increments correlate with those in benzenes, as well as with the Swain-Lupton constants. The ¹³C chemical shifts of some 5-substituted 8-mercapto-, 8-(methylthio)-, and 8-hydroxyquinolines were investigated. Their values are in satisfactory agreement with the additive contribution. of the increments of the substituents. The deviations from additivity are associated with the steric hindrance to interaction of the substituents with the ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 932–936, July, 1981.     

Acyl chlorides of 2,2,5,5-tetramethyl-3-imidazolin-1-oxyl-4-0-acylhydroximic acids

Acylation of nitroenamine derivatives of imidazolidin-1-oxyl with carboxylic acid chlorides leads to 0-acylhydroximic acid chloride derivatives of 3-imidazolin-1-oxyl. The reaction proceeds apparently through a nitrile oxide. It was shown for the 0-benzoyl derivative that reaction of the obtained acyl chlorides with nucleophilic reagents usually gives products of chlorine atom substitution with simultaneous cleavage of the acyl group.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 444–450, February, 1991.     

Photochemical degradation of 2,2,5,5-tetramethyl-4-phenyl-3-imidazoline-1-oxyl

The photochemical degradation of 2,2,5,5-tetramethyl-4-phenyl-3-imidazoline-1-oxyl has been studied in solution at room temperature and in glassy matrices at 77 K. Nitrogen(II) oxide is split from the starting radical during the reaction. The quantum yield of the reaction constitutes ～0.2 in a liquid solution at 298 K and ～0.001 in glassy matrices at 77 K. The kinetics of the solid-phase reaction have a stepped character.     

Synthesis and NMR spectra of tetrahydrofuran-2-13C

An original method was developed for the synthesis of THF labeled selectively with the ¹³C isotope at the α-carbon atom. The effective reduction of symmetry brought about by the insertion of the isotopic label removes the excess degeneracy of the spin systems describing the multiplet structure of the ¹H and ¹³C NMR spectra, making it possible to undertake a detailed analysis. Exact values for the ¹H–¹H spin-spin coupling constants through four bonds and also the ¹³C–¹H and ¹³C–¹³C spin-spin coupling constants involving the α-carbon atom were determined for the first time. The isotopic chemical shifts of the protons and ¹³C nuclei caused by replacement of the ¹²C nucleus by ¹³C were determined. These data can be used to construct a quantitative model of the conformational behavior of THF as a molecular system in which pseudorotation in terms of vibrations with large amplitude is realized.     

Carbon-13 NMR studies on 3-phenyl-as-triazine 4-oxides

The substituent chemical shifts of a series of para substituted-3-phenyl-as-triazine 4-oxides were studied using the Swain-Lupton F and R values. This data was compared to that obtained for parasubstituted biphenyls, phenyl pyrroles and phenyl furans. It was found that the substituent chemical shifts in the triazines behaved in a similar manner to that in the biphenyl system.