Chemistry Reference
In-Depth Information
h
D
4h
G
16
16
=
A
1u
A
2g
A
2u
B
n
u
B
n
g
D
4
D
D
C
4v
C
8
2d
2h
4h
A
2
A
u
B
n
B
2
A
u
A
2
B
u
B
n
B
1
A
2
B
g
B
n
g
B
n
u
C
4
S
4
D
2
C
2v
C
4
2h
A
2
A
u
B
n
B
n
B
B
B
u
B
g
C
2
C
i
C
s
2
B
A"
A
u
C
1
Fig. 13 Subgroups of
D
4h
including the point group order, subgroup-supergroup relations, and
symmetry species. The symmetry species of the higher point groups are given next to the lines
connecting to the respective subgroups. Subscripts
n
correspond to
n ¼
1,2 or
n ¼
1-3 as
indicated by the number of lines
Table
4
. For each of the basic conformations the highest point group is listed first,
followed by the subgroups. Corresponding point groups for homomerous,
heteromerous, and substituted BAEs are listed on the same line. In cases where
the reduced symmetry leads to a different conformational type, this is indicated by a
cross reference to the respective point group, which may be found further down in
the same column. It should be noted that the listed conformations need not neces-
sarily be minima. Some may serve as intermediates or transition states in the
dynamic processes characteristic of BAEs. They could also be higher order saddle
points. Furthermore, a specific conformation, (e.g., t-
D
2
) may turn out to be the
global minimum in one BAE and a transition state in a dynamic process in a
different BAE. In certain cases this may also depend on the computational method
employed in the study. The classification presented in Table
4
may also be applied
to vibrationally distorted molecules and to molecules in crystal structures, which
may be distorted by packing forces.
In cases where the point group symmetry allows twisting,
anti
-folding, or
syn
-
folding in addition to the basic conformational mode, this is indicated using
symbols for mixed conformations ta, at, ts, st, au, su, and f. Note that, from a
