Les spectres de resonance magnetique nucleaire due carbone-13 de 43 benzothiazoles ont ete enregistres dans le dimethylsulfoxyde hexadeuterie. Tous les carbones ont ete attribues de facon non ambigue, grǎce aux effets de substituant sur les positions 4, 5, 6 ou 7. Nous discutons des variations des deplacements chimiques en fonction de la nature du substituant en 2 (equation triparametrique du type: Δδ = aF+bR+cQ+d′), de l'annelation en serie benzoheterocyclique et de la tautomerie prototropique en serie benzothiazolique (dans le cas ou le substituant en position 2 represente un groupement OH, SH ou NHR).



The 13C NMR spectra of 43 benzothiazoles have been recorded in DMSO-d6. All carbon atoms have been attributed in an unambigous way owing to substituent effects in position 4, 5, 6 or 7. We discuss variations of chemical shifts as a function of the nature of the substituent in position 2 (equation of type: Δδ = aF+bR+cQ+d′), annelation in the benzoheterocyclic series, and prototropic tautomerism in the benzothiazolic series (in the case of the substituent in the 2-position being an OH, SH or NHR group).

Etudes d'Hétérocycles Pentagonaux Polyhétéroatomiques par RMN du 13C. Effets de Substituant, de la Benzocondensation et Etude de la Tautomèrie Prototropique en Série Benzothiazolique

2.14 – Pyrazines and their Benzo Derivatives

The relationship between the inhibition performances of three benzo derivatives and their structures on the corrosion of copper in 3.5 wt.% NaCl solution

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.

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

13C-NMR-spektren einiger acridon-alkaloide

Carbon-13 NMR chemical shifts and one-bond carbon–hydrogen coupling constants have been obtained at 15·09 MHz. The trends in the carbon chemical shifts obtained for the pyrazines parallel those of monosubstituted benzenes and 2-substituted pyridines, except for the direct effect of substitution where the pyrazines resemble pyridines not benzenes. The substituent effects on the 13C NMR spectra are generally quite similar to those in the 1H NMR spectra. The 13C NMR spectrum of the tautomeric hydroxypyrazine has been compared with the 13C NMR spectra of 2-, 3- and 4-hydroxypyridines. Hydroxy compounds that can exist as a cyclic amide show a large meta substituent effect on the chemical carbon shift.

Carbon-13 NMR spectra of monosubstituted pyrazines†

The 13C NMR chemical shifts and one-bond carbon–hydrogen coupling constants have been obtained for the title compounds in carbon disulphide as solvent. There appears to be little solvent effect on the 13C chemical shifts. The results suggest the order of release of electrons into the ring is O ≫ S > Se.

C. J. Turner

Papers

Carbon-13 NMR spectra of monosubstituted pyrazines†

The 13C NMR spectra and structure of 2,1,3‐benzoxadiazole,‐benzothiadiazole and ‐benzoselenadiazole