What is atom economy?

Atom economy is a concept used to express how efficiently reactant atoms are used during chemical transformations. It is represented as the ratio of the total mass of the desired final product to the total mass of the atoms used to create it.

The atom economy concept was developed by Barry Trost of Stanford University. Syntheses with an ideal atom economy do not waste any atoms during the transformation process. The higher the atom economy, the lower the level of molecular pollution. The Environmental Protection Agency applies the concept of atom economy in one of its 12 principles of green chemistry.