Fatty Acids: Types
- Triglycerides are a form of lipid, made up of one molecule of glycerol with three fatty acids attached to it
- These fatty acids have long hydrocarbon ‘tails’
- Fatty acids occur in two forms:
- Saturated fatty acids
- Unsaturated fatty acids
- Unsaturated fatty acids can be monounsaturated or polyunsaturated
- The difference between these fatty acid types is found in their hydrocarbon tails
Saturated fatty acids
- In saturated fatty acids, the bonds between the carbon atoms in the hydrocarbon tail are all single bonds
- The fatty acid is said to be ‘saturated’ with hydrogen
- This means that each carbon atom in the hydrocarbon tail (except for the final carbon atom) is bonded to two hydrogen atoms
- Saturated fatty acids can be synthesised industrially by hydrogenation (reaction with hydrogen gas) of unsaturated fatty acids
- All the carbon-to-carbon bonds are single bonds in saturated fatty acids
An example of a saturated fatty acid
Unsaturated fatty acids
- In unsaturated fatty acids, the bonds between the carbon atoms in the hydrocarbon tail are not all single bonds
- There is at least one carbon-carbon double bond; a fatty acid with one C=C double bond is known as monounsaturated fatty acid
- In some unsaturated fatty acids, there are many carbon-carbon double bonds; these are known as polyunsaturated fatty acids
- These double bonds can cause the hydrocarbon tail of unsaturated fatty acids to kink (bend slightly), meaning they are not as straight as saturated fatty acids
- The fatty acid is said to be ‘unsaturated’ because the hydrocarbon tail does not contain the maximum number of hydrogen atoms possible
- This is because each carbon atom in a carbon-carbon double bond can only bond to one hydrogen atom (instead of two)
An example of a monounsaturated fatty acid
An example of a polyunsaturated fatty acid
Examiner Tip
You don't need to know the names of various fatty acids, but you should be able to recognise from a diagram whether a fatty acid is saturated, monounsaturated or polyunsaturated (look for any carbon-carbon double bonds)!