Molecular structure of 3,3-diethylpentane (tetraethylmethane) in the gas phase as determined by electron diffraction and ab initio calculations

The molecular structure of 3,3-diethylpentane (tetraethylmethane) in the ga s phase has been determined by electron diffraction and ab initio calculati ons at the MP2/6-31G* level. Five local minima on the potential energy surf ace were located, but only two have significant populations at room tempera ture. The experimental distribution of conformers was found to be 66(2)% wi th D-2d symmetry and 34(2)% with S-4 symmetry, corresponding to an energy d ifference Delta H degrees in favor of the D-2d form of 3.3(2) kJ mol(-1). T he molecule shows significant distortion from regular tetrahedral coordinat ion at the central carbon atom, with two CCC angles in the D-2d form reduce d to 106.7(8)degrees and two angles in the Sq form increased to 110.9(4)deg rees. These distortions are attributed to asymmetry of the electron density distribution around the CH2 groups.