Nitrogen-15 nuclear magnetic resonance spectroscopy. Carbodiimides

High-resolution, 18.25-MHz nitrogen-15 NMR spectra of several carbodiimides (1) have been obtained at the -abundance level. The high-field positions of the ^(15)N resonances of these substances are discussed in terms two different shielding mechanisms. Solvent influences on the ^(15)N and ^(13)C chemical shifts of carbodiimides are small. Both the ^(13)C and ^(15)N spectra of l-ethyl-3-[3-(dimethylamino)propyl]carbodiimidhey drochloride indicate that at least four different structural isomers are present in dimethyl sulfoxide solution at room temperature. Information about the dimerization of carbodiimides in the presence of alkylating agents has been obtained from ^(15)N and ^(13)C NMR.