1. SAM GIRLSCOLLEGE, BHOPAL
DEPARTMENT OF PHYSICAL SCIENCES
SAM GIRLS COLLEGE, BHOPAL

2. SAM GIRLS COLLEGE, BHOPAL
Isomers
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3. SAM GIRLS COLLEGE, BHOPAL
Structural Isomers
Structural isomers have the same molecular formulas but they differ in their structural formulas.
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4. SAM GIRLS COLLEGE, BHOPAL
Stereoisomers
Stereo isomers have the same structural formulas but they differ in their spatial arrangements.
There are two types of stereoisomerism
Geometrical isomerism
Optical isomerism
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5. SAM GIRLS COLLEGE, BHOPAL
Geometrical isomers
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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6. SAM GIRLS COLLEGE, BHOPAL
Geometrical isomers
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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7. Geometric Isomers in alkenes
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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8. Geometric Isomers in Cycloalkanes
Ring structures like C=C restrict rotation and therefore can result in cis and trans isomers
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9. Properties of Geometrical Isomers
The chemical properties of geometrical isomers tend to be similar but their physical properties are different
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10. Properties of Geometrical Isomers
The trans isomer has a much higher melting point. Unlike the cis isomer there is little intra-molecular hydrogen bonding
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11. SAM GIRLS COLLEGE, BHOPAL
Optical Isomers
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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12. SAM GIRLS COLLEGE, BHOPAL
Optical Isomers
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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13. Distinguishing Enantiomers
Optical isomers can be distinguished by the way they interact with plane polarized light
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14. SAM GIRLS COLLEGE, BHOPAL
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.
SAM GIRLS COLLEGE, BHOPAL

15. Distinguishing Enantiomers
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.
SAM GIRLS COLLEGE, BHOPAL

16. Properties of Optical Isomers
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.
SAM GIRLS COLLEGE, BHOPAL