A fundamental principle in green chemistry is atom economy (AE). AE is a measure of how many atoms from the starting materials are incorporated into the desired product. For example, if a reaction incorporates all the reactant atoms into the product of interest, the reaction has a percent AE of 100%. To obtain percent AE for a reaction, we calculate the mass of the desired product that can be formed from a stoichiometric mixture of reactants, and compare this mass with the total mass of that reaction mixture. (In a stoichiometric mixture of reactants, none of the reactants are present in excess; the mole amounts are in the same ratio as the stoichiometric coefficients).

The prime (') on the symbol for the mass of the desired product serves to remind us that this mass is calculated for a stoichiometric mixture of reactants. Use the definition above to calculate the percent AE for the following reactions, both of which can be used to make C₆H₅NH₂, the desired product.

C₆H₆ + (CH₃)₃SiN₃ + 2 F₃CSO₃H + NaOH → C₆H₅NH₂ + N₂ + (CH₃)₃SiOSO₂CF₃ + NaF₃CSO₃ + H₂O

C₆H₆ + HNO₃ + 3 H₂ → C₆H₅NH₂ + 3 H₂O

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% AE = mass (mp) of the desired product P total mass of a stoichiometric mixture of reactants X 100