Unterscheidung symmetrisch substituierter Kohlenstoffringe durch 13C,13C-Spin-Spin-Kopplung. Vergleich von herkömmlicher und INADEQUATE-13C-NMR-Spektroskopie

Distinction of Symmetrically Substituted Carbocyclic Compounds by ¹³C, ¹³C Spin-Spin Coupling. Comparison of Conventional and INADEQUATE¹³C-NMR Spectroscopy ¹³C,¹³C spin-spin couplings allow an easy distinction of symmetrically substituted carbocyclic compounds. On the basis of the number and ratio of ¹³C,¹³C satellite pairs, for instance head to head and head to tail products of photodimerisations can be distinguished. The informations derived from a conventional and an INADEQUATE ¹³C-NMR spectrum are compared.     

13C chemical shifts of Δ1-pyrrolines

¹³C chemical shifts are reported for the ring carbons of several substituted Δ¹-pyrrolines. Average values for methine and methylene ring carbons facilitate structure elucidation of substituted δ¹-pyrrolines by ¹³C NMR spectroscopy.     

13C?13C spin coupling constants in tetrahydronaphthylene,hexahydrobenzanthracene and benzo[a]pyrene derivatives

The ¹³C? ¹³C spin coupling constants have been determined in substituted [1-¹³C]tetrahydronaphthylenes, [5-¹³C]hexahydrobenzanthracenes and [5-¹³C]benzanthracene. In addition, the ¹³C? ¹³C spin coupling constants for 7-hydroxy[7-¹³C]benzopyrene, trans-7,8-dihydro[7-¹³C]benzopyrene-7,8-diol and trans-7,8-dihydro[10-¹³C]benzopyrene-7,8-diol are reported, together with the one-bond carbon-carbon coupling constants between C-4 and C-5 in selected 4,5-disubstituted benzopyrenes. Values for the directly bonded coupling constants and long-range coupling constants are similar to those reported previously for other aromatic and aliphatic systems. Substituent effects on carbon-carbon coupling are compared for similarly substituted cyclic and acyclic systems.     

Carbon-13 NMR studies of substituted naphthalenes. I—complete assignments of the 13C chemical shifts with the aid of deuterated derivatives

Proton-coupled as well as noise-decoupled ¹³C NMR spectra of several substituted naphthalenes have been studied. Complete assignments of the ¹³C signals based on selectively deuterated derivatives and on the ¹³C? ¹H coupling pattern have been made. For the methoxynaphthalenes, acetylnaphthalenes and naphthaldehydes the dominant conformations of the substituents have been deduced from the ¹³C chemical shifts.     

Metal formyl complexes. The reaction of sodium pentacarbonylmanganate with acetic[13C]formic anhydride

The reaction of acetic [¹³C]formic anhydride with sodiumpentacarbonylmanganate proceeds rapidly at 0°C to give ¹³CO substituted pentacarbonylmanganese hydride as the predominant product. The results are consistent with the formation of a short-lived neutral formyl complex, (CO)₅Mn¹³CHO.     

Proximity and the heteroatom effects on the carbon-13 chemical shifts of methyl-substituted phenols,anilines and thiophenols

Upfield substituent-induced ¹³C chemical shifts for aryl carbons of polymethyl substituted benzenes, phenols, anilines and thiophenols were investigated as a function of the proximity between substituents X and CH₃ (X = CH₃, NH₂, OH and SH). The results indicate that the induced shifts of the substituted aryl carbons are, in general, independent of the polar substituent but depend on the number of adjacent substituted aryl carbons. A ?2.0 ppm upfield shift was found for a substituted aryl carbon adjacent to one substituted aryl carbon and a ?3.8 ppm upfield shift for a substituted aryl carbon bound by two substituted aryl carbons. It is suggested that the near additivity of the upfield shifts is the result of changes in the bond order between the aromatic ring carbons in the region of the substituted aryl carbons due to distortion of the ring. The ¹³C chemical shifts of the methyl substituents for methyl substituted phenols, anilines and thiophenols were determined, and it was found that the values could be predicted from the additivity parameters reported for the analogous methylbenzenes plus an additional pair-interaction term associated with the through-space electronic influence of the heteroatom.     

Synthesis and 13C NMR study of some N-substituted 4-iodo- and 3,4-diiodopyrazoles

The synthesis of some novel N-1 substituted 4-iodo- and 3,4-diiodopyrazoles starting from the corresponding NH-pyrazoles is described. On basis of their ¹³C nmr data and those of already known related congeners the influence of iodo- as well as N-1 substituents on pyrazole ¹³C chemical shifts and ¹³C,¹H spin coupling constants is investigated.     

Elektronenstruktur und NMR-Parameter von substituierten 5-Phenyl-2,4-pentadiensäuren

The ¹H and ¹³C NMR chemical shifts as well as vicinal HH coupling constants of substituted 5-phenyl-2,4-pentadienoic acids Ar? CH?CH? CR?CR? COOH are reported and discussed in connection with the molecular structure. The ¹³C chemical shift values show an alternation along the chain and can be linearly correlated to the π-electron charge densities as calculated by use of the PPP-method. The effect of para-substituents and solvents upon the ¹³C chemical shifts can be described in terms of the mutual atom-atom polarizabilities.     

13C-NMR of substituted tetrazoles

Inductive and resonance effects of phenyl substituted tetrazoles from¹³C NMR studies are calculated.¹³C NMR shifts of a series of these compounds is reported and the aminotetrazole—iminotetrazoline tautomerism of the compounds studied is discussed.     

Reaction of methyl tetronate with some amines. Synthesis of substituted 4-aminobut-2-enolides

A series of substituted 4-aminobut-2-enolide derivatives have been synthesized by reaction of a variety of substituted amines with methyl tetronate. The ¹H and ¹³C nmr spectral analysis of all compounds synthesized are given.     

Carbon-13 nuclear magnetic resonance examination of benzonorbornene derivatives. Assignment of site of aromatic ring substitution in benzonorbornen-2-ones

¹³C nuclear magnetic resonance spectra were collected for a series of 5- and 6-monoaromatic ring-substituted benzonorbornadienes and 5-, 6-, 7-, and 8-monosubstituted benzonorbornen-2-ones. ¹³C chemical shifts values were found to be useful in the differentiation of the four monosubstituted aromatic ring isomers of benzonorbornen-2-one (1). We found that the ¹³C NMR spectrum of a substituted benzonorbornen-2-one (A) could be predicted with good accuracy (R² for each aromatic carbon ≥ 0.925) from a knowledge of the ¹³C NMR spectrum of 1 and the appropriately substituted benzene. The substituents studied were NO₂, NH₂, I, CF₃, CN, OCH₃, and H. Correlation analysis showed that the carbonyl in A was effectively insulated from the ring π-system.     

13C NMR spectra of thiophenes. III—Bromothiophenes

The ¹³C NMR spectra of all bromo substituted thiophenes have been obtained at 15·085 MHz. ¹³C signal assignments for monobromothiophenes have been confirmed by comparison with the spectra of their partially deuteriated derivatives; a revision is made for the assignment in 3-bromothiophene. The substituent effect of bromine is generally additive for the ¹³C chemical shifts. The substituent effect on various types of ¹³C, ¹H coupling constants is also obtained and discussed.     

NMR studies on some 1,3,5-triazaadamantane derivatives

¹H and ¹³C data are presented for eleven 1,3,5-triazaadamantane derivatives. Ring protonation produces a decrease in ¹H screening and the opposite effect in the corresponding ¹³C spectrum. The trisaryl substituted compounds appear to exist as a single isomer with diequatorial and monoaxial substituents.     

An interpretation of 1H and 13C chemical shifts in substituted benzenes on the basis of M.O. charge densities

The results of an MOLCAO calculation on both σ and π electron systems of several substituted benzenes are reported. The charge densities obtained reproduce the dipole moments of the molecules examined, provided that substituents with strong mesomeric effects are not present. It is shown that there is a satisfactory agreement between ¹³C and ¹H chemical shifts and the trend of total charge densities for all positions of substituted benzenes.     

13C NMR spectra of benzodiazepinones: Application to isomeric structure determination

A ¹³C NMR study of a number of substituted 1,5-benzodiazepin-2-ones has been carried out, and shows that this technique is one of the rare spectroscopic methods which allows an unambiguous identification of the number and nature of the isomers formed in the condensation of a β-ketoester with a substituted O-phenylenediamine.     

13C n.m.r. of organosulphur compounds: II—13C chemical shifts and conformational analysis of methyl substituted thiacyclohexanes

¹³C n.m.r. spectra of methyl substituted thianes and thianium cations have been determined. The magnitude of the ¹³C substituent effects of an equatorial methyl group or of a gem-dimethyl grouping appear to depend in a systematic way on whether the carbon atom concerned is adjacent to, or removed from, the heteroatom. The shieldings are discussed in relation to the conformational properties of the thiane ring. Moreover, the average ¹³C substituent parameters obtained from conformationally biased systems are applied to potentially mobile systems to assess the position of the conformational equilibrium.     

Carbanion chemistry : By R.B. Bates and C.A. Ogle,Springer-Verlag,Berlin etc., 1983, viii + 117 pages,DM 48

Rotational barriers have been determined from an analysis of exchange-broadened line-shapes in ¹³C NMR spectra of substituted tricarbonyl(cyclohexadienyl)iron(I+) salts.     

1H- und 13C-NMR-spektroskopische Untersuchungen zur Ladungsverteilung in substituierten 1,3-Dioxan-2-ylium-Salzen

The ¹H and ¹³C NMR spectra of a series of 1,3-dioxan-2-ylium salts substituted at C-2 and C-4, C-5, C-6 have been measured. The atomic charge distribution in 1,3-dioxan- and 1,3-dioxolan-2-ylium cations has been calculated with the MINDO/3 method, leading to a linear correlation between π-charge and ¹³C chemical shift at C-2. The strong C-21-proton downfield shift is caused by the anisotropic influence of the mesomeric cation system. The conformations of substituted 1,3-dioxan-2-ylium cations are discussed.     

Studies in sulphur heterocyles. 2—The 13C NMR spectra of thienocoumarins

¹³C NMR spectra of 3- substituted thieno[2,3-h][1]benzopyran-2-ones and 8-substituted thieno[3,2-f]-[1]benzopyran-7-ones are reported and the substituent dependence of certain ¹³C chemical shifts is noted.     

Substituent effects on 13C chemical shifts of ketenimines: a GIAO/HF and DFT study

GIAO/HF and DFT methods were utilized to predict the ¹³C chemical shifts of substituted ketenimines. GIAO HF/6–311+G(2d,p) and B3LYP/6–311+G(2d,p) methods were applied on the optimized B3LYP/6–31G(d) geometries and ¹³C chemical shifts of C_α and C_β of substituted ketenimines were correlated with group electronegativities. HF and DFT calculations indicated that increasing substituent group electronegativity leads to increasing chemical shift of C_β of substituted ketenimines, whereas the C_α values decrease. Copyright © 2003 John Wiley & Sons, Ltd.