Molecular Structure of 3,3-Diethylpentane (Tetraethylmethane) in the Gas Phase As Determined by Electron Diffraction and ab Initio Calculations

• Published in: Journal of organic chemistry 1999-06, Vol.64 (12), p.4226-4232
• Main Authors: Alder, Roger W, Allen, Paul R, Hnyk, Drahomír, Rankin, David W. H, Robertson, Heather E, Smart, Bruce A, Gillespie, Ronald J, Bytheway, Ian
• Format: Article
• Language: English
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo981779m

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 2 d symmetry and 34(2)% with S 4 symmetry, corresponding to an energy difference ΔH° in favor of the D 2 d 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 2 d form reduced to 106.7(8)° and two angles in the S 4 form increased to 110.9(4)°. These distortions are attributed to asymmetry of the electron density distribution around the CH2 groups.