Chapter 07 · Materials & footprintsCircular Economy & Materials
Atom economy
Definition
The percentage of the total formula weight of all reactants that is incorporated into the desired product: % atom economy = (formula weight of desired product ÷ sum of formula weights of all reactants) × 100. Developed by Barry Trost (1991), it is the second of the Twelve Principles of Green Chemistry: synthetic methods should maximise incorporation of all materials used into the final product.
References
Definition and formula; Trost (Science 1991) origin; worked example (50% at 100% yield); relationship to other green metrics.
Overview
What it means
Atom economy complements yield: a reaction can have 100% yield yet poor atom economy if much of the reactant mass ends up in by-products (the classic ACS worked example scores 50% despite perfect yield).
Because it is calculated from the balanced equation, it measures intrinsic wastefulness of a route before any process considerations such as solvents, which are captured by complementary metrics (E-factor, process mass intensity).
How it is used
Chemists use atom economy to compare synthetic routes at the design stage, favouring addition and rearrangement reactions over substitutions and eliminations. In industry it is combined with yield, E-factor and PMI to drive greener processes, especially in pharmaceuticals.
Why it matters
Atom economy embeds waste prevention — rather than end-of-pipe treatment — into chemical design. It is a foundational concept linking chemistry to circular-economy and pollution-prevention goals.