Pteridine studies: III—13C n.m.r. data of pteridine,some of its derivatives and their covalent σ-adducts with ammonia and water

¹³C n.m.r. spectral data of pteridine and nineteen of its derivatives (containing one or more chloro, methylthio, methyl, t-butyl or phenyl substituents) are reported. The ¹³C n.m.r. spectrum of the title compound has been assigned conclusively. ¹³C n.m.r. substituent effects are shown to be very useful in discerning between 6- and 7-substituted pteridines. Additionally, the ¹³C n.m.r. spectra of several covalent amination products, i.e. the 3,4-dihydro-4- amino- and the 5,6,7,8-tetrahydro-6,7-diaminopteridine derivatives, formed by dissolving the appropriate pteridine in liquid ammonia, have been recorded. The ¹³C n.m.r. spectra of the corresponding covalent hydrates are also reported.     

1H- und 13C-NMR-untersuchungen an dibromoxabicyclo[n.2.1]alkanen

The ¹H n.m.r. spectra of some dibromooxabicyclo[n.2.1]alkanes are discussed for the determination of the configuration and conformation. The ¹³C n.m.r. spectra confirm the observed stereochemistry. With increasing ring size the ¹³C n.m.r. chemical shifts of the hetero atom substituted C-atoms C-1 and C-2 move steadily to lower fields.     

A 13C n.m.r. study of the charge-transfer complexes between o-chloranil and some aromatic electron donors

The ¹³C n.m.r. spectra of complexes between o-chloranil and aromatic electron donors were studied. Complexation leads to a general diamagnetic shift of the ¹³C n.m.r. signals for the acceptor (o-chloranil), but for signals from the ¹³C nuclei in the donors both diamagnetic and paramagnetic shifts are found. These phenomena are thought to be the result of competing anisotropy and charge-migration effects. Charge migration in o-chloranil complexes appears to be more important than in corresponding 1,3,5-trinitrobenzene complexes.     

Nitrogen-15 n.m.r. studies of 13C, 15N labeled arginine

¹⁵N n.m.r. spectra of [¹³C-2, 3-¹⁵N₂-guanidino]arginine and [¹³C, ¹⁵N₂] urea were obtained in D₂O and H₂O at a variety of pH values both with and without proton decoupling. The effects of the proton exchange rate are readily observable in the proton coupled ¹⁵N spectra. When the guanidino group is deprotonated (pK = 12.5), the terminal nitrogens give a single resonance 6.6 ppm downfield of the protonated species, indicating a rapid tautomeric exchange. The observed NH and CN couplings are compared with calculated values, and good agreement is found for ¹J(CN) using a Blizzard–Santry type calculation. The ramifications of the proton exchange on ¹⁵N n.m.r. spectra of amino acids and peptides are discussed.     

Carbon-13 n.m.r. and CNDO/S study of 1,3-indandione and heterocyclic analogues

¹³C n.m.r. spectra are reported for 1,3-indandione, phthalic anhydride, thiophthalic anhydride, and phthalimide in chloroform-d solution. The ¹³C chemical shifts have also been calculated by means of Pople's perturbation theory using CNDO/S wave functions; the agreement between theoretical and experimental values is improved when an empirical charge-dependent term is added to the calculated diamagnetic and paramagneitc contributions.     

N.m.r. spectra of prostaglandin metabolites and precursors and of related pyrazoline adducts

The ¹³C n.m.r. spectra of the major human urinary metabolite of prostaglandin PGE₂ and PGE₁ are discussed together with some unsaturated precursors. Δ-2-Pyrazolines, formed by addition of diazomethane to the 11-oxo dienediones in this series, were identified by ¹³C and ¹H n.m.r. and by other physical methods.     

Carbon-13 n.m.r. investigation on the nitrogen methylation of the mono- and diazanaphthalenes

The ¹³C n.m.r. spectra of the N-methylated mono- and diazanaphthalenes have been recorded and analysed. It has been shown that N-methylation as well as N-protonation in cinnoline occur predominantly at the β-nitrogen atom. N-methylation and N-protonation show a similar effect on the ¹³C chemical shifts.     

The case for a revised structure for hypophyllanthin - an analysis of the 13C N.M.R. spectra of aryltetralins

A revised structure for hypophyllanthin is proposed on the basis of its ¹³C n.m.r. spectrum. ¹³C n.m.r. spectra also support the previously proposed structure for nirtetralin and assist in the structural elucidation of a new aryltetralin lignan.     

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.     

Carbon-13 isotope effect on proton decoupled 13C and 31P n.m.r. spectra of bis(diphenylphosphino)acetylene

High resolution proton decoupled ¹³C and ³¹P n.m.r. spectra of bis(diphenylphosphino)acetylene in (CD₃)₂SO and CDCl₃ are analysed as ABX spectra to give the relative chemical shifts of the ¹³C and ³¹P nuclei as well as the spin–spin coupling constants ³J(PP) and ⁿJ(PC). The differences in ³¹P shieldings are due to secondary ¹³C isotope effects which have been observed to be negligible over more than two bonds.     

13C n.m.r. spectra of rotameric dimethyl 1-isopropyldibenzo[b,e]bicyclo[2.2.2]octatriene-7,8-dicarboxylate: Non-equivalency of carbons along the rotational axis

¹³C n.m.r. spectra of dimethyl 1-isopropyldibenzo[b,e]bicyclo[2.2.2]octatriene-7,8-dicarboxylate disclose the existence of both dl and meso isomers, whereas ¹H n.m.r. spectra were interpreted by the sole existence of the former. Characteristic chemical shifts for the rotamers were found, among others, for carbons along the rotational axis. The non-equivalence is most probably attributed to the difference in geometry about the carbons in question. An unusual fact was also that the more compressed methyl carbon of the isopropyl group gives a signal at higher field.     

13C NMR spectroscopy of polycyclic aromatics. VIII—amino derivatives of quinoline,isoquinoline, acenaphthene and fluoranthene

Complete assignments of the ¹³C n.m.r. spectra have been made for 5-aminoquinoline, 5-aminoisoquinoline, 5-aminoacenaphthene and 3-aminofluoranthene. Substituent-induced shifts are compared with those of the structurally related 1-aminonaphthalene. Some deviations within the series can be interpreted in terms of an increase of the exocyclic peri angle. An analysis of the ¹H n.m.r. spectrum of 3-aminofluoranthene is also given.     

RMN du 13C de Bromo et de Fluoro Cyclanones à Structure Contrainte: Variation des Effets α et γ en Fonction des Facteurs Stériques et de la Nature de l'Halogène

¹³C n.m.r. spectra of various halo-bicyclo[3.2.1]octan-3-ones and 7,7-dimethylbicyclo[3.1.1]heptan-3-ones are described. It is possible to correlate in an empirical way the α and γ effects with the geometric features of these molecules. Thus, the reflex and anti-reflex effects can be studied by ¹³C n.m.r. spectroscopy.     

Borchelate und Bormetallchelate, 4. Mitt.

The i.r., u. v.,¹H n.m.r.,¹³C n.m.r., and¹¹B n.m.r. spectra of several substituted diphenylboron chelates derived from salicylaldehyde azomethines were compared with respect to the influence of the amine substituentR. O–B–N-6-ring constitution of the chelates29–32 [R=OH, NH₂, NHC₆H₅, N(CH₃)₂] can be deduced from the spectra.

Als 3. Mitt. gilt:F. Umland undE. Hohaus mit Beiträgen vonW. Riepe, K. Brodte, C. Schleyerbach undD. Szonn. Untersuchungen über borhaltige Ringsysteme vom Chelattyp. Forschungsbericht des Landes Nordrhein-Westfalen Nr. 2538. Opladen: Westdeutscher Verlag. 1976.     

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.     

Structural studies by 1H and 13C dynamic n.m.r.: Part III alternative protonation sites in carbonyl conjugated enamines of the type R1?C(O)?CH?CH?NR2R3

¹³C magnetic resonance spectra of several enamino ketones with secondary and tertiary amino groups were obtained for trifluoroacetic acid solutions. In both series O-protonation is predominant and the chemical shifts are related to the electron density changes with respect to the parent base. The spectra of the tertiary compounds are interpreted in terms of slow rotation around the C–1? C–2 and C–3? N bonds discernible at room temperature. O-protonated forms of the secondary enamino ketones undergo further reaction on C–2 yielding pyridinium salts. The mechanism of formation of the quaternary salts is interpreted and the additivity parameters of the ¹³C n.m.r. chemical shifts in the pyridinium ions is briefly discussed.     

13C n.m.r. spectra of some thiobenzamides. Correlation between 13C and 1H n.m.r. spectra and signal assignments of syn and anti CH2 groups

¹³C n.m.r. spectra of a series of N,N-disubstituted thioamides have been recorded and signal assignments were performed. Separate signals are observed for methylene groups fixed on the nitrogen atom. Since the carbon atom syn to the thiocarbonyl sulfur resonates at higher field than the anti carbon, the syn-anti assignment in ¹H n.m.r. is easily obtained by selective double irradiation. This method, which is rapid and reliable, affords a rather general solution to the interesting problem of resonance assignments in tertiary amides and thioamides (and in analogous molecules such as oximes and nitrosamines).     

Effects of simultaneous 13C?1H and 13C?11B decoupling on the carbon-13 n.m.r. spectra of some organoboron compounds

¹³C FT n.m.r. spectra were obtained from borates of methyl α-D -glucopyranoside, triethylboron, sodium tetraphenylboron and 1-butaneboronic acid employing a simultaneous ¹H and ¹¹B decoupling network. The effectiveness of the system was evident using the three latter organoboron compounds. Since no diminution in line broadening of signals occurred in the spectrum of the sugar borate, the absence of ¹³C? O? ¹¹B coupling was indicated. This finding was confirmed by comparing the effects of varying the temperatures of sugar borates and triethylboron on their conventional ¹³C n.m.r. spectra.     

13C n.m.r. investigation on the nitrogen methylation of some azabenzenes

The ¹H and ¹³C n.m.r. spectra of N-methylated pyridine, pyridazine, pyrimidine and pyrazine and N,N-dimethylated pyrimidine and pyrazine have been recorded and analysed. The change in the ¹³C chemical shifts under the influence of N-methylation (Δδ) in the diazabenzenes could be predicted by the Δδ values of pyridine. A comparison of the Δδ values of N-methylation with those of N-protonation showed that both reactions have a similar effect.     

Nuclear magnetic resonance spectral study of 2-acetylpyridine4 N-alkylthiosemicarbazones and their cobalt(III) complexes

¹H and¹³C n.m.r. spectra are reported for a series of 2-acetylpyridine⁴ N-alkylthiosemicarbazones in order to study the effect of increased size of the alkyl function on the ratio of isomers present in solution. Similarly, n.m.r. data for the bis(thiosemicarbazone)cobalt(III) complexes are included, as well as these complexes' ligand field parameters. TMC 2698