The eclipsed non-alternating ground-state conformation for 1,1,2-tri-t-butylethane. Molecular mechanics calculations and NMR spectrum

Staggered conformations of the title compound are calculated by Allinger's MM282 molecular mechanics program to be less stable than a conformation in which t-butyl groups and ethane hydrogens are near to eclipsed with dihedral angles of +5.4°, +23.5° and –3.2°. The Newman projection is non-alternating with the H–C–H projection within the t-butyl-C-t-butyl projection. The vicinal NMR proton–proton coupling constant reflects this eclipsing. Evidence is adduced for other molecules with near-to-eclipsed ground states.