C NMR chemical shifts are reported for several alkyl or aryl amines, acetamides, diacetamides and ammonium and trimethylammonium salts. Substituent effects, determined with respect to chemical shifts of amino derivatives, are rationalized in terms of y effects, steric interactions and, for benzene derivatives, in terms of competition between inductive (a,) and resonance (uR) effects. These perturbations can be used to assign chemical shifts of complex structures and to study certain chemical processes. 13

Thirty-four benzoxazoles, oxazole, and 10 o-aminophenols have been studied by 13C nmr spectroscopy. All the signals have been attributed from substituent effects. The structure of products obtained by nitration of benzoxazole have been determined by 13C nmr. The shifts induced by substitution at the 2 position have been discussed as a function of an empirical model using the structural parameters F, R, and Q*. Azido–tetrazole equilibria (N3 in position 2) and prototropic tautomerism (NH2, OH, and SH in position 2) have been also discussed. The chemical shifts and coupling constants of oxazole and unsubstituted benzoxazole have been compared.

The -C chemical shifts of 1-phenyl-2-pyrazoline and 25 N-nitropheny1-2-pyrazolines, with different substituents on the heterocyclic ring, have been assigned. These values are discussed as a function of the steric and electronic nature of the various substituents. The steric effects produced conformational modifications, both in the nitrophenyl and 2-pyrazoline moieties, which explain some of the chemical shifts.Les dkplacements chimiques du carbone-13 de la phknyl-1 pyrazoline-2 et de vingt-cinq N-nitrophhyl pyrazolines-2, diversement substitukes sur I'hCtCrocycle, ont Ctk complktement attribuks. Ces valeurs sont discutkes en fonction des contraintes klectroniques et stkriques des diffkrents substituants. Les effets stkriques entrainent des modifications de la conformation aussi bien du groupement nitrophknyle, que du cycle pyrazoline-2, ce qui explique les variations de certains dkplacements chimiques. AITRIBUTION DES DEPLACEMENTS CHIMIQUESA partir de critbres classiques, telle que I'analyse des spectres partiellement dCcouplCs, et en utilisant certaines donnkes de la littkrature, en particulier les effets de substituants en skrie benzknique,6 nous avons pu attribuer I'ensemble des dkplacements chimiques du composC l a et des dCrivks de la sCrie 2 .