Atom economy

Atom economy is the fraction of reactant atoms retained in the desired product, calculated from the balanced reaction equation. It measures how efficiently a chemical reaction uses its starting materials.

Stoichiometry: The quantitative relationships between reactants and products in chemical reactions. Balanced stoichiometry supplies the coefficients and formulas used to calculate atom economy.
Green chemistry: The design of chemical products and processes that reduce or eliminate hazardous substances and waste. Atom economy is a central design principle for reducing waste at the reaction-planning stage.
Reaction efficiency: A broad assessment of how effectively a chemical process converts inputs into useful output. It can combine yield, selectivity, energy use, and waste, unlike atom economy’s equation-based scope.
Addition reaction: A reaction in which atoms or groups add to a molecule, often without eliminating a small molecule. Addition reactions often retain most reactant atoms in the main product.
Balanced chemical equation: A chemical equation with equal numbers of each type of atom on both sides. Its coefficients determine how many reactant atoms are available for the desired product.
E-factor: A measure of process waste calculated as the mass of waste produced per mass of product. It captures actual waste quantities that atom economy alone does not account for.
Selectivity: The preference of a reaction for forming one product over competing products. High selectivity can reduce byproducts in practice, but does not change atom economy for a fixed equation.
Substitution reaction: A reaction in which one atom or group in a molecule is replaced by another. The displaced group becomes a by-product, illustrating how atom economy can fall.
Theoretical yield: The maximum amount of product predicted from reactant quantities and reaction stoichiometry. Like theoretical yield, atom economy is calculated from the reaction equation rather than experimental losses.
Process mass intensity: The total mass of materials used in a process divided by the mass of product made. It broadens material accounting beyond the reactant-to-product ratio in atom economy.

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