Introduction to constitutional (structural) isomers
Constitutional (structural) isomers are compounds that have the same molecular formula but a different atom-to-atom bonding sequence.
The constitutional isomers below each have a different carbon skeleton (arrangement of carbon atoms). Therefore, they have different physical properties and can be separated from each other.
Compounds that have the same carbon skeleton but have multiple bonds between different carbon atoms are also constitutional (structural) isomers. Two such isomers are shown below.
The constitutional isomers below each have a different carbon skeleton (arrangement of carbon atoms). Therefore, they have different physical properties and can be separated from each other.
 |  |  |
| C6H14 boils at 63 °C | C6H14 boils at 50 °C | C6H14 boils at 58 °C |
Compounds that have the same carbon skeleton but have multiple bonds between different carbon atoms are also constitutional (structural) isomers. Two such isomers are shown below.
CH3CH2CH=CH2
CH3CH=CHCH3