NMR-STUDY OF NITROGEN INVERSION PROCESS IN SOME ISOXAZOLIDINES

A series of isoxazolidines with substituents at various ring positions has been synthesised and their NMR spectra recorded over a range of temperatures. The NMR spectra at low temperatures indicate the presence of two isomers due to slow nitrogen inversion, except in 10, 16, and 17. The nitrogen inversion barriers are determined using complete line-shape analysis, and their dependence on solvent and steric factors is discussed. For the isoxazolidines with substitutions at the 2, 5 and 2, 3 positions, the trans compounds become the major and the sole isomer, respectively.