The deuterium distribution observed in isobutane recovered after
short contact times with the DF−SbF5
superacid at 0 °C shows that a very fast reversible protonation of
all C−H bonds occurs before ionization of the
alkane, in accord with the Olah σ-basicity concept. Comparison
of the amounts of hydrogen with the amount of
tert-butyl ions generated during ionization shows that the
reaction is purely protolytic in HF containing up to 20
mol
% SbF5, but becomes oxidative at higher
concentrations.