AN NMR-STUDY OF INVERSION ISOMERISM IN 1-OXA-10-AZABICYCLOR[5,3,0]DECANES

The NMR spectra of many 1-oxa-10-azabicyclo[5,3,0]decanes, with substituents at the 2 and 3 positions, showed the presence of two isomers of unequal populations at -40-degrees-C. The major isomer is shown to be the trans conformer which is in equilibrium with a minor isomer (cis conformer) by a relatively slow nitrogen inversion process. The barriers to nitrogen inversion were determined by the NMR band shape analysis and were in the range 53 to 56 kJ/mol-1.