How do side reactions affect percentage yield and atom economy?

Side reactions decrease the percentage yield and atom economy by producing unwanted products and consuming reactants.

In more detail, side reactions are reactions that occur alongside the main reaction. They can be problematic in chemical reactions because they use up some of the reactants that would otherwise be used in the main reaction. This means that less of the desired product is produced, which reduces the percentage yield. The percentage yield is a measure of the efficiency of a reaction, calculated by comparing the actual amount of product made to the maximum possible amount. If side reactions occur, the actual amount of product made is less than it could be, so the percentage yield is lower.

Side reactions also affect atom economy. Atom economy is a measure of how well atoms are utilised in a reaction, calculated by comparing the total mass of useful products to the total mass of all products. If a side reaction occurs, some atoms are used to make unwanted products. This means that the total mass of useful products is less than it could be, so the atom economy is lower.

For example, consider a reaction where A and B react to form C, but there is also a side reaction where A reacts with D to form E. Some of the A that could have been used to make C is instead used to make E. This reduces the amount of C that can be made (lowering the percentage yield) and means that some atoms are used to make E rather than C (lowering the atom economy).

In conclusion, side reactions can significantly impact the efficiency of chemical reactions, reducing both percentage yield and atom economy. This is why chemists often work to minimise side reactions in order to maximise the efficiency of their reactions.