The nuclear magnetic resonance spectra of N-nitroso-N-alkyl amino acids

Structurally related acyclic and cyclic N-nitroso-N-alkyl amino acids were prepared and their ¹H, ¹³C and ¹⁵N NMR spectra were investigated. The changes in the ¹³C NMR spectra of the N-nitroso α-amino acids after dissolving in solvents suggest that they posses the Z-configuration in the crystalline state; in solution some of them isomerize to mixtures of the Z- and E-isomers whose composition appear to depend on steric factors. The ¹³C chemical shifts were assigned on the basis of anisotropic effects of the nitrosamino group and configurational stability. The ¹³C chemical shifts were correlated with those of the nitrosamines of the same carbon skeletons and the effects of changing a methyl group to the carboxylic acid are deshielding on the α-carbons and shielding on the β-carbons.