Chemistry Reference
In-Depth Information
Table 13 Possible point groups and conformations of the transition state for conformational
inversion of the
syn
-folded conformation s-
C
2v
(
x
)
Group of permutation-inversion operators
h
TS
n
TS
Cp
a
b
TS
{
E
, (18)(1
0
8
0
), (11
0
)(88
0
)(99
0
), (18
0
)(81
0
)(99
0
),
E
*,
(18)(1
0
8
0
)*, (11
0
)(88
0
)(99
0
)*, (18
0
)(81
0
)(99
0
)*}
p-
D
2h
8
2
1
1
C
2v
(
x
)B
3u
{
E
, (18)(1
0
8
0
), (11
0
)(88
0
)(99
0
), (18
0
)(81
0
)(99
0
)} t-
D
2
4 4 1 2
C
2
(
x
)
3
{
E
, (18)(1
0
8
0
),
E
*, (18)(1
0
8
0
)*} p-
C
2v
(
z
) 4 412
C
s
(
xz
)B
1
{
E
, (11
0
)(88
0
)(99
0
),
E
*, (11
0
)(88
0
)(99
0
)*} p-
C
2v
(
y
)4 412
C
s
(
xy
)B
1
{
E
, (18
0
)(81
0
)(99
0
), (18)(1
0
8
0
)*, (11
0
)(88
0
)(99
0
)*} s-
C
2v
(
x
) 4 412
C
2v
(
x
)A
1
{
E
, (18)(1
0
8
0
), (11
0
)(88
0
)(99
0
)*, (18
0
)(81
0
)(99
0
)*} pt-
C
2h
(
z
)4 4 12
C
s
(
xy
)B
u
{
E
, (11
0
)(88
0
)(99
0
), (18)(1
0
8
0
)*, (18
0
)(81
0
)(99
0
)*} a-
C
2h
(
y
)4 412
C
s
(
xz
)B
u
{
E
, (18
0
)(81
0
)(99
0
), E*, (18
0
)(81
0
)(99
0
)*} p-
C
2h
(
x
)4 412
C
2
(
x
) A
u
{
E
, (18)(1
0
8
0
)} t-
C
2
(
z
) 2814
C
1
B
{
E
,(1
0
)(88
0
)(99
0
)} ta-
C
2
(
y
)2 814
C
1
B
{
E
, (18
0
)(81
0
)(99
0
)} ts-
C
2
(
x
) 2 814
C
2
(
x
) A
{
E
,
E
*} p-
C
s
(
yz
) 2 814
C
1
A
00
{
E
, (18)(1
0
8
0
)*} f-
C
s
(
xz
) 2 814
C
s
(
xz
)A
0
{
E
, (11
0
)(88
0
)(99
0
)*} s-
C
s
(
xy
) 2 814
C
s
(
xy
)A
0
{
E
, (18
0
)(81
0
)(99
0
)*} a-
C
i
2 8 1 4
C
1
A
u
{
E
} ft-
C
1
1618
C
1
A
a
Point group symmetry along pathway from transition state to reactant or product, i.e., maximum
common subgroup of transition state and reactant or product
b
Symmetry species of the mode of the transition vector (using the conventional setting of the
transition state point group [
279
])
Fig. 27 Schematic
mechanism of the inversion
of the
syn
-folded
conformation s-
C
2v
(
x
) via a
planar transition state p-
D
2h
1'
1
p
Z
1'
1
1'
s
Z-RS'
s
1
Z-SR'
1'
p
1'
1
1'
s
s
1
E-RR'
E-SS'
The degree of folding of both moieties is reduced in a synchronous manner,
retaining
C
2v
(
x
) symmetry along the pathway until the planar transition state is
reached. Increasing the folding in the opposite direction leads to the inverted
conformation. The transition vector leading to products and reactants has B
3u
symmetry. Note that this planar transition state is the same conformation that was
considered as a high symmetry transition state for the inversion of the
anti
-folded
conformation (Fig.
23
). However, a bona fide transition state can only have steepest
descent paths to two minima [
248
,
270
]. Due to the high degree of overcrowding,
p-
D
2h
is expected to be a higher order saddle point with more than one imaginary
frequency and steepest descent paths to several minima, transition states, and/or
