A dynamic nuclear magnetic resonance study of nitrogen inversion in N , N '‐dimethylimidazolidine

The 251 MHz 1 H and the natural‐abundance 63.1 MHz 13 C NMR spectra of N , N '‐dimethylimidazolidine have been measured from −50 to −170°C. Below about −140°C. nitrogen inversion in the compound becomes slow on the NMR time scale and both the 1 H and the 13 C spectra indicate that it exists in solution as a mixture of cis and trans conformations having nearly the same energies. The free‐energy barrier (ΔG ≠ ) for nitrogen inversion in N , N '‐dimethylimidazolidine is 6.4 kcal mol −1 , a value which is 1.5 kcal mol −1 lower than that for N ‐methylpyrrolidine.