Chemistry Reference
In-Depth Information
E
(18)(1'8')
(18)
(1'8')
1'
1'
1
1
1'
1'
1
1
Z-P
Z-P
E-P
E-P
(11')(88')(99')
(18')(81')(99')
(11'88')(99')
(18'81')(99')
1
1'
1'
1
1
1'
1
1'
1
Z-P
Z-P
E-P
E-P
E*
(18)(1'8')*
(18)*
(1'8')*
1
1
1'
1'
1
1'
1
1'
Z-M
Z-M
E-M
E-M
(11')(88')(99')*
(18')(81')(99')*
(11'88')(99')*
(18'81')(99')*
1'
11'
1
1
1
1'
1
1'
Z-M
Z-M
E-M
E-M
Fig. 30 Effect of the permutation-inversion operators on the twisted conformation t-
D
2
Table 15 Effect of permutation-inversion operators on the twisted conformation t-
D
2.
Permutation-inversion operators Effect on conformation t-
D
2
E
, (18)(1
0
8
0
), (11
0
)(88
0
)(99
0
), (18
0
)(81
0
)(99
0
) None
a
E
*, (18)(1
0
8
0
)*, (11
0
)(88
0
)(99
0
)*, (18
0
)(81
0
)(99
0
)* Inversion of helicity
(18), (1
0
8
0
), (11
0
88
0
)(99
0
), (18
0
81
0
)(99
0
)
E
,
Z
-Isomerization
(18)*, (1
0
8
0
)*, (11
0
88
0
)(99
0
)*, (18
0
81
0
)(99
0
)*
E
,
Z
-Isomerization and inversion of helicity
a
E
, (18)(1
0
8
0
), (11
0
)(88
0
)(99
0
), (18
0
)(81
0
)(99
0
) correspond to the point group symmetry operators,
E
,
C
2
(
z
),
C
2
(
y
), and
C
2
(
x
)oft-
D
2
, respectively
Enantiomerization of the Twisted Conformation
The point groups and conformations of possible transition states for the
enantiomerization of the twisted conformation t-
D
2
, predicted by the molecular
symmetry group are listed in Table
16
. The point group order
h
TS
, number of
versions
n
TS
, connectivity
C
, number of parallel pathways
p
, the symmetry along
the pathways, and the symmetry species of the transition vector are also given. Note
that the symmetry operators of t-
D
2
,
E
, (18)(1
0
8
0
), (11
0
)(88
0
)(99
0
), and (18
0
)(81
0
)
(99
0
) and the operators inverting the helicity of this conformation,
E*
, (18)(1
0
8
0
)*,
(11
0
)(88
0
)(99
0
)*, and (18
0
)(81
0
)(99
0
)* combine to give the point group
D
2h
. All
subgroups of
D
2h
are also considered as possible point groups.
The conformation p-
D
2h
is the transition state with highest possible symmetry
(
h
8) for the enantiomerization of t-
D
2
. There are two versions of the transition
state, p
Z
and p
E
, interconverting the
Z
- and
E
-versions of the twisted conformation,
ΒΌ
