What is the difference between atom economy and percentage yield?

Atom economy measures the amount of starting materials that become useful products, while percentage yield compares actual yield to theoretical yield.

Atom economy and percentage yield are both important concepts in chemistry, particularly in the field of green chemistry and industrial processes. However, they measure different aspects of a chemical reaction.

Atom economy is a measure of the amount of starting materials that end up as desired products. It is a theoretical concept, calculated by comparing the total molecular mass of the desired products to the total molecular mass of all products. A high atom economy means that most of the material ends up in the desired product, which is more efficient and environmentally friendly. This is because it reduces waste and the need for raw materials. Atom economy is particularly important in industrial chemistry, where efficiency and sustainability are key.

On the other hand, percentage yield is a measure of how much product is actually produced in a reaction compared to the maximum amount that could theoretically be produced. It is calculated by comparing the actual yield (the amount of product actually obtained) to the theoretical yield (the maximum amount that could be produced according to the balanced chemical equation). A high percentage yield means that the reaction was very efficient, with little of the reactants being wasted or ending up as unwanted by-products. However, in reality, it is often not possible to achieve a 100% yield due to factors such as incomplete reactions, side reactions, or loss of product during separation and purification.

In summary, while both atom economy and percentage yield are measures of efficiency in chemical reactions, they focus on different aspects. Atom economy looks at how efficiently atoms are utilised in a reaction, while percentage yield looks at how much of the theoretical product is actually obtained.