Chemistry Reference
In-Depth Information
t
P
-
D
2
t
P
-
C
2
(
z
)
ts
E-RPR
'
-
C
2
(
x
)
ta
Z-RPR
'
-
C
2
(
y
)
Fig. 16 Three-dimensional projections of the twisted conformations of homomerous,
heteromerous, and disubstituted BAEs including their point group symmetry operators
t
P
-
C
2
(
z
) and t
M
-
C
2
(
z
) conformations.
E
-or
Z
-disubstitution may introduce
syn
-
folding or
anti
-folding, respectively. The various twisted conformations and their
point groups are illustrated in Fig.
16
.
Note that ts
E-RPR
0
-
C
2
(
x
)andta
Z-RPR
0
-
C
2
(
y
) (and their enantiomers ts
E-SMS
0
-
C
2
(
x
)
and ta
Z-SMS
0
-
C
2
(
y
), respectively) correspond to the case where the substituents
require additional out-of-plane deformation due to increased overcrowding as in
the 1,1'-difluoroderivatives of bifluorenylidene (2) [
205
]. Reduced out-of-plane defor-
mation at the substituents would lead to ts
E-SPS
0
-
C
2
(
x
)andta
Z-SPS
0
-
C
2
(
y
)(andtheir
enantiomers ts
E-RMR
0
-
C
2
(
x
)andta
Z-RMR
0
-
C
2
(
y
), respectively) as illustrated in Fig.
17
.
anti
-Folded Conformations
Symmetric
anti
-folded conformations of homomerous BAEs may have the point
group
C
2h
(
y
). Non-equivalent tricyclic moieties in heteromerous BAEs lead to au-
C
s
(
xz
) with unequal degrees of folding.
E
-Disubstitution leads to a
E-RS
0
-
C
i
. Note
that there is no twist of the central double bond due to symmetry constraints. The
folded substituted tricyclic moieties are chiral, albeit with opposite absolute
