Tetranitromethane: A Nightmare of Molecular Flexibility in the Gaseous and Solid States

After numerous attempts over the last seven decades to obtain a structure for the simple, highly symmetric molecule tetranitromethane (C(NO2)4, TNM) that is consistent with results from diffraction experiments and spectroscopic analysis, the structure has now been determined in the gas phase and the solid state. For the gas phase, a new approach based on a four‐dimensional dynamic model for describing the correlated torsional dynamics of the four C−NO2 units was necessary to describe the experimental gas‐phase electron diffraction intensities. A model describing a highly disordered high‐temperature crystalline phase was also established, and the structure of an ordered low‐temperature phase was determined by X‐ray diffraction. TNM is a prime example of molecular flexibility, bringing structural methods to the limits of their applicability. Highly dynamic is the structural behavior of tetranitromethane, C(NO2)4. After more than half a century of investigations, its structure in the gas phase was solved through the development and application of a new approach for the dynamic modeling of electron diffraction data while the refinement of single‐crystal X‐ray diffraction data has now been successful for two phases.