MAGNETIZATION-TRANSFER NMR-STUDY OF NITROGEN INVERSION IN 2,2-DIMETHYLAZIRIDINE

The slow inversion at pyramidal nitrogen in 2,2-dimethyiaziridine was investigated by NMR spectroscopy at 304 K using one-dimensional spin l ocking methods and two-dimensional exchange spectroscopy. The activati on 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 unimolec ular inversion barrier height as autocatalytic and water-catalyzed inv ersion pathways can in principle also contribute to the observed rate. The spin locking experiments described employ non-selective pulses an d 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.