Aziridines nitrogen pyramidal inversion

Oxaziridines For oxaziridines the N-inversion barrier is considerably higher than that for similar aziridines. A-Alkyloxaziridines show a high degree of configurational stability of the pyramidal nitrogen with inversion barriers... 

Table 2. Activation parameters for pyramidal nitrogen inversion from NMR data Aziridines and substituted aziridinesa)...

Incorporation of d-functions on the inverting N site is especially important. Such functions contribute more to the pyramidal GS than to the TS and thus stabilize the GS with respect to the TS. In the absence of -functions on N, the inversion barrier in NH3 is found to be much too small and H2N—CN and H2N—SiHs are found to be more stable in the planar form inclusion of -functions (and p on H) leads to the correct NH3 barrier 158> and to pyramidal nitrogen sites in HaN—CN and H2N— SiH3 (Table 8 144>). Of course, the relative error introduced by the absence of -functions is smaller the higher the barrier. This may explain in part why the barriers calculated for aziridine and oxaziridine without including -functions are in satisfactory agreement with experimental values. In PH3, the phosphorus inversion barrier changes from 30.9 to 37.2 kcal/mole on inclusion of two sets of -functions 159>. 

Trisubstituted atoms with a lone pair, such as amines, may undergo the process of pyramidal atomic inversion on the NMR time scale. The resonances of the two methyls in the aziridine 5-15 become equivalent at elevated temperatures through rapid nitrogen inversion. 

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