N.m.r. studies on aromatic compounds. I—13C n.m.r. spectra of some mono- and disulpho-substituted hydroxycarboxylic acids

Carbon-13 n.m.r. spectra of 3-hydroxy-4-sulpho-2-naphthoic, 3-hydroxy-5-sulpho-2-naphthoic, 3-hydroxy-7-sulpho-2-naphthoic, 5-sulphosalicylic, 3-hydroxy-5,7-disulpho-2-naphthoic, 1-hydroxy-4,7-disulpho-2-naphthoic, and 3,5-disulphosalicylic acids were recorded with and without proton noise-decoupling. Analyses of the spectra were carried out for all compounds except 3-hydroxy-5-sulpho-2-naphthoic acid which dimerized. The fine splitting caused by long-range coupling was used in identifying the lines of the ¹³C n.m.r. spectra.     

Carbon-13 n.m.r. spectra of saturated heterocycles. Part VII—Thianium Salts

The ¹³C n.m.r. spectra of 53 thianium, S-methylthianium, S-alkylthianium and S-methyl-1-thiadecalinium salts, most of them substituted with methyl groups in the ring, have been recorded. The chemical shifts of the ring carbons in these thianium and S-methylthianium salts and the S-methyls in the S-methylthianium salts have been analyzed in terms of additive parameters of the methyl substituents which are compared to those previously determined for the parent thianes. Comparison is also made with other charged species.     

Conformational study of phosphoserine in aqueous solution. I—13C n.m.r. results

¹³C chemical shifts and coupling constants of phosphoserine in aqueous solutions were studied as a function of pH values. Carboxyl and α-amino titration shifts agree with those observed in amino acids. The analysis of the coupling constants indicates that for rotation about the (C)? C? O? (P) axis the trans conformer predominates for all pH values. The fractional population of the gauche conformer reaches a maximum at pH=8.     

Determination of the conformation of 1,4-diheterocyclanes. I—The 1H n.m.r. spectrum and ring conformation of 3-methyl-2-oxo-1,4-dioxepane

The ¹H n.m.r. spectrum of 3-methyl-2-oxo-1,4-dioxepane was recorded at 300 and 60 MHz. The ring conformation was considered in terms of the spectral parameters and shown to be a twisted boat where the lactone grouping is approximately planar.     

13C n.m.r. spectra of steroids —a survey and commentary

The literature on ¹³C n.m.r. examinations of steroids has been reviewed and the shielding data for over 400 examples are tubulated. The assignments for each compound have been considered and, where necessary, revised in the light of more recent evidence and for consistency throughout each series. The methods available for assignments are reviewed and, in many cases, illustrated with specific examples. The major practical features concerning ¹³C studies of steroids are discussed as a guide to the use of the technique. From the main body of shielding data, an extensive set of substituent effects has been generated to aid the examination of new systems. The utility and the limitations of these effects are described.     

13C n.m.r. spectra of lysergic acid derivatives: II—dihydrolysergamides

The conformations of dihydrolysergamides and 10-methoxydihydrolysergamides have been inferred from the study of the chemical shifts of the amide hydrogens and their temperature dependence. The ¹³C chemical shifts have been shown to be sensitive to conformational changes of the piperidine ring. The results indicate that the conformation of the latter depends both on the substituent in position 10 and on the solvent.     

Carbon-13 n.m.r. studies: 68—diastereomeric nonequivalence and the characterization of some bisnorbornylpinacols

The sodium-ammonia reduction of racemic norcamphor, exo-3-methylnorcamphor and 3,3-dimethyl-norcamphor (camphenilone) leads to substantial yields (60–90%) of the corresponding 2,2′-bisnorbornyl-2,2′-diols as diastereomeric mixtures. A combination of their ¹H, ¹³C and infrared spectra together with the results of periodic acid and lead tetraacetate oxidations permits stereochemical assignments for these six pinacols.     

Conformational study of diastereomers. V—assignment of RR and RS relative configurations to 2,2,6,6-tetramethyl-5-phenyl-3-heptanol by proton n.m.r.

Assignment of RR and RS configurations to 2,2,6,6-tetramethyl-5-phenyl-3-heptanol diastereomers has been carried out through an analysis of the observed values for vicinal coupling constants of both isomers and their conformational distribution. The latter was previously estimated from steric interaction energies between groups. Since the RR isomer is monoconformational its magnetic parameters can be used to carry out conformational analysis of related acyclic compounds.     

Nuclear magnetic resonance studies: VII—13C and 15N n.m.r. of diazo compounds

The ¹³C and ¹⁵N n.m.r. results for a series of diazo compounds are reported. It is found that the diazo carbon is shielded by an extraordinary amount compared with normal sp² hybridized carbons. The ¹⁵N chemical shifts reveal that the terminal nitrogen is deshielded relative to the central one. This is contrary to that expected from charge effects but support is found for this phenomenon in other systems. One-bond ¹³C? ¹⁴N coupling in diazomethane is also reported for the first time. INDO MO calculations of the charges and finite perturbation calculations of ¹³C? ¹⁴N and C? H couplings are compared with the experimental results.     

Conformational study of phosphoserine in aqueous solutions. II—1H n.m.r. results

The 270 MHz n.m.r. spectra of phosphoserine (PSer) have been measured and completely analysed for seven pD values. The resulting vicinal coupling constants ³J(HαHβ) and ³J(PHβ) are used to discuss the conformations of PSer with respect to the (Hα)? Cα? Cβ? (O) and (Cα)? Cβ? O? (P) bond axes. The all-trans conformer predominates for all pD values, with its fractional population being minimal at pD values close to neutrality. The Cβ? O bond rotamer populations agree reasonably well with those obtained from ¹³C investigations.     

Carbon-13 n.m.r. studies. 65—13C spectra of some tricyclo[3.2.1.02,4]octane derivatives

The ¹³C n.m.r. spectra of 18 derivatives of the tricyclo[3.2.1.0^2,4]octanes have been determined. This series includes methyl, hydroxyl and oxo substituted examples to compare the effects of these substituents on the skeletal carbon shieldings with those observed for the corresponding norbornanes and bicyclo[3.2.1]octanes. In general, the trends are similar and the perturbations associated with closely neighboring groups follow a consistent pattern. The shielding data for the exo–exo and exo–endo isomers of tetracyclo[3.3.1.0^2,40^6,8]nonane are also reported.     

1H n.m.r. spectra and ensuing conformational evidence on carbon–carbon double bonded systems. (Electrically neutral organic Lewis acids—33)

The n.m.r. spectra of various derivatives of the cyclic acylal of malonic acid and of dimethylbarbituric acid are described. From the long range coupling constant, conformational evidence on the dihedral angle θ between the aromatic ring and the diketodioxane ring or the N,N-dimethylbarbituric acid ring can be derived. The investigated substances show a dependence of θ on the aromatic substitution.     

2,3,5,6-Tetramethylmorpholine: II—1H n.m.r. structural studies of the isomers of 2,3,5,6-tetramethylmorpholine

The structures of the six isomers of 2,3,5,6-tetramethyl-morpholine have been determined by means of proton nuclear magnetic resonance studies at 100 MHz. The spectra have been analysed in terms of spin–spin coupling constants and population distributions of the possible conformers at low temperatures. Also included in this paper are results from n.m.r. studies on the six 4-benzyl-2,3,5,6-tetramethylmorpholine derivatives, which give information about the stereochemistry of the methyl groups α to the amine group.     

Isobenzopyryliumsalts: VII—13C n.m.r. shifts of 1-arylisobenzopyrylium salts and correlation with Hammett parameters

The signal identifications of isobenzopyrylium salts has been achieved on the basis of proton broad-band and off-resonance decoupled ¹³C n.m.r. spectra of twelve different 1-arylisobenzopyrylium salts and eight model compounds. From the ¹³C shifts valuable information about pK values, the aromatic character and the conjugative effects of isobenzopyrylium salts was obtained.     

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.     

The 13C n.m.r. spectra of polysubstituted benzenes. 1—the use of hexachlorobenzene as a reference for the structure elucidation of multisubstituted polychlorobenzenes

The use of ¹³C n.m.r. for structure elucidation of a series of products obtained by reaction of dialkylamines with 1,2-dinitrotetrachlorobenzene has shown that the general problem of non-additivity of substituent effects of contiguously substituted benzenes may be overcome, with these products, by the choice of a suitable standard. In this case hexachlorobenzene was used and the difference between the actual and calculated chemical shifts was small, allowing unambiguous structural assignment.     

N.m.r. studies in the heterocyclic series: XVI—determination of the structure of 3-azidoindazole by 1H and 13C n.m.r. spectroscopy

The 1-NH structure for 3-azidoindazole has been demonstrated by the observation of ¹H? ¹H and ¹³C? ¹H couplings involving the hydrogen atom attached to nitrogen. A comparison between 3-azidoindazole and indazole shows that both compounds have the same tautomeric structure.     

The n.m.r. spectra of porphyrins. 13—A ring current model for the porphyrin and chlorin (7,8-dihydroporphyrin) rings

The equivalent dipole model of the ring current shift in benzene is shown to be equivalent to that of the well-known two current loop calculation. A network model of the ring current effect in the porphyrin system is described, using the double–dipole approximation, to give a calculation of the ring current shifts in the porphyrin system; this agrees with the observed shifts of protons both in the ring-plane and above it. A simple modification of the model enables treatment of ring current shifts in the chlorin ring. These models may be used to provide, very simply, good estimates of the ring current shifts of the porphyrin and chlorin rings at points above and outside the current loops; the agreement is sufficiently good to allow assignments of peripheral substituents to be made, and to provide information on their orientation. The model is consistent with a peripheral ring current loop in both the free-base porphyrins and their metal complexes. The relationship of these results to calculations in polycyclic aromatics and to protonation shifts in porphyrins is discussed.     

N.m.r. spectra of cyclic amines. II—Factors influencing the chemical shifts of α-protons in aziridines

Proton magnetic resonance spectra of trans and cis-2,3-diphenylaziridine (1 and 2) and their N-ethyl derivatives 3 and 4 were measured in carbon tetrachloride, chloroform, and benzene-d₆ at low temperatures (1 and 3) and in dry conditions (1 and 2). On the basis of these results it was concluded that an N-ethyl group exerts a shielding influence on a cis ring proton and a deshielding influence on a trans ring proton. From results obtained by measuring the ¹H n.m.r. spectra of 1–4 in deuterochlorofom-trifluoroacetic acid it was derived that the lone pair of the aziridine nitrogen exerts a shielding influence on cis related ring hydrogens. In most N-alkylaziridines the effect of the N-alkyl group predominates.