The X-ray structures of three simple heterocyclic compounds have been obtained for the first time. Structures both 3-acetyloxazolidin-2-one 1 and its unsaturated analogue 3-acetyloxazolin-2-one 3 show a planar imide nitrogen with exocyclic C=O oriented anti to ring N–C(=O) bond negligible intermolecular interactions, pattern consistent previously reported analogues. In contrast parent NH hetero...