Magnetization transfer NMR study of nitrogen inversion in 2,2-dimethylaziridine

The slow inversion at pyramidal nitrogen in 2,2-dimethylaziridine was investigated by NMR spectroscopy at 304 K using one-dimensional spin locking methods and two-dimensional exchange spectroscopy. The activation free energy was found to be 17.5 kcal mol−1 (73.2 kJ mol−1) at this temperature. This value represents a lower limit for the unimolecular inversion barrier height as autocatalytic and water-catalyzed inversion pathways can in principle also contribute to the observed rate. The spin locking experiments described employ non-selective pulses and are particularly useful for the quantitative study of slow chemical exchange between nuclei of similar resonance frequency where selective magnetization transfer experiments are difficult or impossible.