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 gas phase has been determined by electron diffraction and ab initio calculations at the MP2/6-31G* level. Five local minima on the potential energy surface were located, but only two have significant populations at room temperature. The experimental distribution of conformers was found to be 66(2)% with D-2d symmetry and 34(2)% with S-4 symmetry, corresponding to an energy difference Delta H degrees in favor of the D-2d form of 3.3(2) kJ mol(-1). The molecule shows significant distortion from regular tetrahedral coordination at the central carbon atom, with two CCC angles in the D-2d form reduced to 106.7(8)degrees and two angles in the Sq form increased to 110.9(4)degrees. These distortions are attributed to asymmetry of the electron density distribution around the CH2 groups.