Chemistry Reference
In-Depth Information
s
-
C
2v
(
x
)
su
-
C
s
(
xz
)
st
E-RPR
'
-
C
2
(
x
)
s
Z-RS
'
-
C
s
(
xy
)
Fig. 19 Three-dimensional projections of the
syn
-folded conformations of homomerous,
heteromerous, and disubstituted BAEs including their point group symmetry operators
syn
-Folded Conformations
Symmetric
syn
-folded conformations of homomerous BAEs may have point group
C
2v
(
x
). Non-equivalent tricyclic moieties in heteromerous BAEs lead to su-
C
s
(
xz
),
which has the same point group as au-
C
s
(
xz
) (Fig.
18
) and f-
C
s
(
xz
).
E
-Disubstitution leads to st
E-RPR
0
-
C
2
(
x
), with the same point group as ts
E-RPR
0
-
C
2
(
x
) (Fig.
16
).
Z
-Disubstitution results in s
Z-RS
0
-
C
s
(
xy
), a
meso
conformation. In the
last case, twisting is not compatible with the point group. Typical examples of
syn
-
folded conformations are illustrated in Fig.
19
.
Folded Conformations
The folded conformation f-
C
s
(
xz
) may be envisioned as a conformation with one
folded and one (nearly) planar moiety, as, e.g., in the folded conformation of
fluorenylidene-xanthene (5) (Fig.
20
). For homomerous and heteromerous BAEs,
such a conformation may have
C
s
(
xz
) symmetry. Moreover, the conformational
type f-
C
s
(
xz
) may also be used to describe folded conformations with unequal
degrees of folding, when it is not known whether the relative direction of folding is
syn
or
anti
(au-
C
s
(
xz
)orsu-
C
s
(
xz
)). Twisting the central ethylene group reduces
