1. Isomers
Molecules with same molecular formula but their respective atoms are arranged differently in space 1

2. Structural Isomers
Structural isomers have the same molecular formulas but they differ in their structural formulas. 2

3. Examples
butane and methylpropane
ethanol and methoxymethane

4. 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 4

5. Geometrical isomers
Geometrical isomers occur in organic molecules where rotation around a bond is restricted
This occurs most often around C=C
Example:
cis-but-2-ene and trans-but-2-ene 5

6. 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 6

7. Geometric Isomers in Cycloalkanes
Ring structures restrict rotation and therefore can result in cis and trans isomers 7

8. Properties of Geometrical Isomers
The chemical properties of geometrical isomers tend to be similar but their physical properties are different 8

9. Optical Isomers
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) 9

10. Optical Isomers
While these structures may look identical, in three dimensions they are mirror images of each other.
Such molecules are called enantiomers. 10

11. Task Draw the structural isomers for C4H10O. How many do you get?