Ab initio molecular orbital and density functional
theory (DFT) calculations were performed to investigate
energies, geometries, and reactivities of halomethyl cations and their
protonated analogues. On the basis of calculated
energies the observed superelectrophilic activation of the halomethyl
cations in superacid solutions is discussed.
The protonated halomethyl cations have considerable kinetic and
thermodynamic stability. 13C NMR chemical
shifts
of selected systems were calculated by IGLO method and compared with
experimental data.
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.
A series of oxonium and carboxonium ions and their
corresponding protonated dications were investigated
by ab initio/IGLO/GIAO-MP2 methods. The calculated
17O and 13C NMR chemical shifts were compared
with the
solution phase experimental data for the monocations. The
structures and energies of a number of oxonium and
carboxonium dications and the effect of diprotonation on the
17O and 13C NMR chemical shifts were also
studied.
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