Chemistry Reference
In-Depth Information
c.
4
5
3
6
2
1
(
Z
)-1,4-hexadiene; there is no stereochemistry at the double bond joining C-1
and C-2 because both substituents at C-1 are identical (=CH
2
).
d.
There is no stereochemistry at either double bond. The IUPAC name is
1,5-hexadiene.
5.40
Trans
-1,2-dibromoethene and
cis
-1,2-dibromoethene are configurational isomers
(they can only be interconverted by breaking and remaking a bond, in this case the
pi-bond of the alkene), they are both achiral (their mirror images are identical to
themselves), and they are diastereomers (although they are stereoisomers, they are
not enantiomers).
5.41
The structure has one double bond and one stereogenic center (C-4). Four isomers
are possible (
R
or
S
at C-4 and
E
or
Z
at the double bond).
CH
H
H
CH
3
3
C
C
C
C
4
4
H
CH
H
CH
H
3
3
Cl
H
l
(
R,E
)
(
S,E
)
H
H
H
H
C
C
C
C
4
4
CH
CH
H
CH
CH
3
3
3
3
Cl
H
l
(
R,Z
)
(
S,Z
)
The upper and lower sets form two pairs of enantiomers.
5.42
a.
2
*
5
1
3
4
6
*
CH
3
C
H
C
H
C
H
C
H
CH
3
Cl
Cl
Compare with part b. In this case, both stereogenic centers are identical.
Therefore, two
meso
forms are possible, and the total number of isomers is
reduced to six:
R
,
Z
,
R
R
,
Z
,
S
(meso)
R
,
E
,
R
R
,
E
,
S
(
meso
)
S
,
Z
,
S
S
,
E
,
S
There are two sets of enantiomers:
