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.
Mono- and diprotonated guanidines were prepared in superacid
solutions and studied by 1H, 13C, and
15N
NMR spectroscopy. The structures, energies, and NMR chemical
shifts were also calculated by ab initio/IGLO/GIAO-MP2 method. Excellent agreement were found between
experimental and calculated 13C and 15N NMR
chemical
shifts. No persistent triprotonated guanidine was observed.
Tri- and tetraprotonated guanidines were also studied
by ab initio/IGLO/GIAO-MP2 method.
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