Kk. Laali et al., Superacid protonation of dihydrocyclobuta[e]pyrene and its C-60-o-quinodimethane adduct. An NMR, ab initio/GIAO and AM1/PM3 study, J CHEM S P2, (10), 1999, pp. 2129-2132
Citations number
38
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 2
Dihydrocyclobuta[e]pyrene 1 is protonated in FSO3H-SO2ClF to give a ca. 2 :
1 mixture of two arenium ions of alpha-protonation 1H(+) and 1aH(+). Ab in
itio/GIAO theory at the B3LYP/6-31G(d,p) level was utilized to calculate th
e NPA charges, relative energies and to predict the NMR chemical shifts for
1H(+) and 1aH(+) as a means to enhance the solution NMR-based assignments.
The resulting regioisomeric arenium ions are highly delocalized and exhibi
t a uniform charge alternation path within a pyrenium moiety. Reasonable pr
edictions of their relative energies and the overall charge delocalization
mode can also be obtained at the AM1/PM3 levels. In an attempt to determine
the influence of C-60 on tropicity in an anchored-pyrenium ion, the C-60-o
-quinodimethane adduct 2 was protonated in FSO3H . SbF5-SO2ClF; formation o
f regioisomeric bound-arenium ions (2H(+), 2aH(+)) which are very poorly so
luble in superacid media was inferred from H-1 NMR and AM1/PM3 calculations
were used to model these cations. Further model studies using a fragment o
f C-60 bound to regioisomeric pyrenium ions were realized at the LSDA/DN le
vel of theory with electrostatic potential derived charges at the B3LYP/6-3
1G(d,p) level.