  Hyperconjugation is a basic conception of chemistry. Its straightforward
effect is exhibited by the spatial delocalization characteristics of the
electron density distributions or wavefunctions. Such effects on the electron
wavefunctions of the highest-occupied molecular orbitals (HOMO) of two ethanol
conformers are demonstrated with electron momentum spectroscopy together with
natural bond orbital analyses, exhibiting the distinctly different symmetries
of the HOMO wavefunctions in momentum space.
