Structural investigations of ylides. Part I. Crystal and molecular structures of trimethylammoniobenzamidate and trimethylammonionitramidate: two stabilised nitrogen–nitrogen ylides

Crystal structure analyses of the title compounds (IIa) and (III) have been carried out with diffractometer data. Both were solved by direct methods and refined by least-squares techniques to R 0·072 [(IIa), 977 reflexions] and 0·078 [(III), 378 reflexions]. Crystal data are: (IIa), monoclinic, space group P21/c,Z= 4, a= 11·620(10), b= 7·928(6), c= 11·454(10)A, β= 113·75(3)°; (III), orthorhombic, space group Pnma, Z= 4, a= 12·245(6), b= 6·718(3), c= 7·099(5)A. The results of the analyses indicate significant charge delocalijsation on the oxygen atoms of the stabilising benzoyl- and nitro-groups respectively. In both molecules the quaternary nitrogen and delocalised anionic moieties adopt a syn-planar relationship, this conformation resulting in possible interactions between oxygen and methyl-hydrogen atoms in each case In compounds (II; a–d) temperature invariant n.m.r. spectra, consistent with a single conformation in solution, were obtained.