DYNAMIC NUCLEAR MAGNETIC-RESONANCE STUDY OF NITROGEN INVERSION IN N,N'-DIMETHYLIMIDAZOLIDINE

The 251 MHz 1H and the natural‐abundance 63.1 MHz 13C 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 1H and the 13C 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. Copyright © 1979 Heyden & Son Ltd.