A-Level/ Advanced Higher Chemistry course notes. Concise notes summarising the topic of stereochemistry. Notes are easy to follow and contain a summary of the topic with highlighted key-points and supportive examples where appropriate.
STEREOCHEMISTRY
Isomers molecules that have the same molecular formula but a different structural
formula
stereoisomers occur when the order of bonding in the atoms is the same but the spatial
arrangement of the atoms is different in each isomer There are two types of stereoisomer
geometric and optical
G E OM E T R l C 1 S OM E R I S M
Also known as cis trans isomerism
Geometric isomerism occurs when there is restricted rotation around a carbon carbon double
bond or a carbon carbon bond in a cyclic compound
c C bonds can also be referred to as pi it bonds
Geometric isomers must have two different groups attached to each of the carbon
atoms that make up the bond with restricted rotation
Geometric isomers can be labelled cis or trans according to whether the substituent groups
are on the same side cis or on different sides trans of the bond with
restricted rotation
C IS TRANS
The cis isomer has the Trans isomerhas
groups on the SAME groups on the OPPOSITE
side of the carbonbonds sides of the carbon
with restricted rotation bondswithrestrictedrotation
Although commonly found in organic molecules containing a c c bond geometric isomerism is also
found in saturated ringswhererotationaroundthe C C bonds are restricted
, v v
H H
U C u C
l H
c c c c
H H H H H L
cis 1,2 dichlorocyclopropane trans 1,2 dichlorocyclopropane
Naming Geometric Isomers
H H H Cl
c c c
a Cl a H
cis 1,2 dichloroethene trans 1,2 dichloroethene
To get geometric isomerism there must be
RESTRICTED ROTATION involving a c c bond or a saturated
ring
structure
TWO DIFFERENT GROUPS on each end of the c c or c C bond
it doesn't matter whether the lefthand groups are the same
as the righthand ones or not
Fats 31Oils Higher revision
COOCH COOCH
i
COOCH COOCH
i n i
COOCH COOCH
cc
f a
cc
in the cis form the two hydrocarbon in the trans form the two hydrocarbon
groups are on the same side groups are on opposite side ofthe c c
the lack of rotation about the C C bond bond This doesn't cause quite as much
puts a permanent kink into the chain distortation
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