1. Isomers
C2.4
Organic Compounds

2. What is an isomer?
Molecules that have the same molecular formula but a different structure of atoms are called isomers.
There are three main types:
Chain isomers
Positional isomers
Functional group isomers

3. Chain isomers
Chain isomers occur when the carbon chain of a molecule is arranged differently. For example:

4. Chain isomers
Have a go at drawing and naming three chain isomers of C5H12

5. Positional isomers
Positional isomerism occurs when the functional group remains the same, but is in a different position within the molecule. E.g
This can also apply to alkenes where the position of the double bond changes.

6. Positional isomers
Have a go at drawing and naming three positional isomers of C5H11Cl

7. Functional group isomers
In this type of isomerism, the atoms all stay the same, but they are rearranged so that the functional group changes. E.g.
aldehyde ketone

8. Isomerism in Alkenes Alkenes can also undergo structural isomerism:
There can be branching within the molecules – Chain isomerism
The position of double bond can change – Position isomerism

9. Knowledge check
1. Draw the four structural isomers of C4H9Cl and name them.
2. Draw the three isomers of C4H8 containing a C=C bond.
3. Draw the five structural isomers with the formula C6H14 and name them.

10. Knowledge check
Try the isomers and nomenclature worksheet…

11. Past paper questions