Chemistry Reference
In-Depth Information
p
-
D
2h
p
-
C
2v
(
z
)
p
E
-
C
2h
(
x
)
p
Z
-
C
2v
(
y
)
Fig. 14 Three-dimensional projections of the planar conformations of homomerous,
heteromerous,
E
-, and
Z
-disubstituted BAEs including their point group symmetry operators
symmetry point of view, the magnitude of the contributions of two modes in a
mixed conformation is irrelevant. The point group and symmetry properties are
identical. However, the conformations may look significantly different (see below).
Any conformation combining three modes (t, a, and s) of out-of-plane deformation
has point group
C
1
. Formally
C
1
(
{
E
}) is a subgroup of every point group. Thus
the corresponding conformations symbolized by ft-
C
1
(or tf-
C
1
) should be listed as
possible sub-groups for each conformation type (except for p, which by definition
has a minimum symmetry of
C
s
). However, there is no symmetry information in
this fact, and thus ft-C
1
is included only once at the bottom of the table rather than
repeated for every conformational class.
Planar Conformations
The (hypothetical) planar conformation p of a homomerous bistricyclic aromatic
ene has point group symmetry
D
2h
or one of its subgroups. Characteristic examples
are shown in Fig.
14
. The point group
C
2v
(
z
) corresponds to cases where the two
moieties are not equivalent, e.g., in heteromerous BAEs. The point group
C
2v
(
y
)is
characteristic for
Z
-disubstituted BAEs.
E
-Disubstitution leads to point group
C
2h
(
x
). The point group
C
s
(
yz
) corresponds to a loss of all elements of symmetry
except for the plane of the molecule. In conformations pt with the point group
C
2h
