Download Isomers

OEP-OCUP-WINTER-2015
NAME : SOHIL CHAMADIYA
BRANCH : CHEMICAL
SEM : 3rd
ENROLLMENT : 140470105006
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Structural isomers have the same
molecular formulas but they differ
in their structural formulas.
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Stereo isomers have the same
structural formulas but they differ in
their spatial arrangements.
There are two types of
stereoisomerism
1.
2.
Geometrical isomerism
Optical isomerism
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Geometrical isomers occur in organic
molecules where rotation around a bond is
restricted
This occurs most often around C=C
The most common cases are around
asymmetric non-cyclic alkenes
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Carbon to carbon double bonds are made up of a s and a
p bond.
The p bond is formed from the combination of two p
orbitals, one from each of the two carbon atoms
The two p orbitals must be in the same plane to combine
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A cis isomer is one in which the substituents
are on the same side of the C=C
A trans isomer is one in which the substituents
are on the opposite sides of the C=C
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Ring structures like C=C restrict
rotation and therefore can result in cis
and trans isomers
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The chemical properties of geometrical isomers tend to
be similar but their physical properties are different
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The trans isomer has a
much higher melting point.
Unlike the cis isomer there
is little intra-molecular
hydrogen bonding
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Optical isomerism is present in all
compounds that contain at least one
asymmetric (chiral) carbon atom
An asymmetric carbon atom has four
different atoms or groups attached
In this case there are
two different ways to
arrange the four groups
around the chiral
carbon atom (shown in
red)
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While these structures may
look identical, in three
dimensions they are mirror
images of each other. Such
molecules are called
enantiomers.
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Optical isomers can be distinguished by the way
they interact with plane polarized light
Polarized light is light that has been passed through a
polarizing prism or filter. As a result the light vibrates in a
single plane.
Optical isomers can be distinguished by the way they
interact with plane polarized light. One enantiomer will
rotate polarized light to the right, the other to the left.
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Apart from their optical activity enantiomers generally
have similar physical and chemical properties.
The chemical properties may be significantly different
when the enantiomers interact with other optically active
compounds.
Thalidomide has two optical isomers.
One is a tranquilizer, the other is a
Powerful teratogen.