Electron Density in Long Carbon–Carbon Bonds

Abstract

THE crystal structures of ammonium oxamate and lithium oxalate have been studied by X-ray diffraction methods. Three-dimensional intensity data were collected with a xenon-filled proportional counter using copper K α-radiation. Refinement of the three positional and six anisotropic vibrational parameters for each atom, including hydrogen, was carried out by the method of least squares; convergence occurred at R = 0.044 for ammonium oxamate and R = 0.060 for lithium oxalate. At this stage, three-dimensional F_O–F_C Fourier syntheses were computed. These are shown in the form of superimposed sections in Figs. 1a and b. Contours are drawn at intervals of 3σ, where σ is the root mean square deviation of electron density averaged over the whole unit cell.