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the same common synthetic intermediate by DDQ (dichlorodicyanobenzoquinone) oxidation, demethyla-
tion and oxidation. All of these
OPO
s are very stable in air in the solid state for a few months. In addition,
8-hydro
43
and 8-(
p
-halophenyl)
45
derivatives of
6OPO
were also designed and prepared. Both neutral
radicals are stable enough to handle in air in the solid state.
The electronic structures of
TB4OPO
and
TB6OPO
were investigated using solution EPR
1
H-ENDOR/
TRIPLE studies. Figure 3.35 shows the EPR spectra of
4OPO
and
6OPO
, and the hfccs determined in terms
of these spectra and quantum chemical calculations. The spin delocalized natures and “spin topological
symmetry control” phenomena predicted by theoretical calculations are experimentally demonstrated.
Figure 3.36b - d shows the possible tautomers of 7-hydroxy-
TB6OPO
depending on the delocalized
nature of the unpaired electron based on the
6OPO, 4OPO
,and
9OPO
/
π
-electronic structures, respectively.
(a)
(b)
Figure3.35
Experimentally and theoretically (in parentheses) obtained hfccs of
1
H, spin density distributions,
andhyperfineEPRspectrafor(a)
TB4OPO
and(b)
TB6OPO
. (b Reprintedwithpermissionfrom[43].Copyright
2000AmericanChemicalSociety.)
O
O
O
O
H
H
H
O
O
O
O
HO
O
O
O
(a)
(b)
(c)
(d)
(e)
Figure3.36
(a)Alocalspinstructurehavingadominantcontribution,(b-d)possibletautomersbasedon
6OPO,
4OPO
,and
9OPO
π
-electronicstructures,respectively,and(e)spindensitydistributionof7-hydroxy-
TB6OPO
.
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