An Electron Diffraction Investigation of Dimethylketene Dimer

An electron diffraction investigation of dimethylketene dimer confirms the 2,2,4,4-tetramethylcyclobutadione-1,3 structure. The following parameters were determined for the symmetrical model: C–C (ring)=1.56±0.05A, C–CH3=1.54±0.05A, C=O=1.22±0.04A, ∠C–CO–C=93°±6°, and ∠CH3–C–CH3=111°±6°. The limits of error assigned to the angles apply only if simultaneous variation is excluded; otherwise much larger limits must be assigned. A notable feature of the structure is the large temperature factor which must be ascribed to the interatomic distances greater than 3A. The relation of this temperature factor to the unusually large atom polarization is discussed in terms of the probable amplitudes of the pertinent modes of vibration of the molecule.