1H NMR spectra of a series of 1-benzyl- and 1,3-dibenzylimidazolidines are analyzed and correlated with their conformational features. The spectra are assigned on the basis of chemical shifts and proton coupling constant values, and confirmed by NOESY spectra. C 2 -Unsubstituted imidazolidines (1, 9) show a fast inversion of the nitrogen atoms. By contrast, 1,2,3-trisubstituted imidazolidines display a preferential conformation with a transoid orientation of the N 1 , N 3 , and C 2 substituents.