The conversion of a substrate into a particular product, irrespective of reagents or mechanisms involved. For example, the transformation of aniline ($\ce{C6H5NH2}$) into N-phenylacetamide ($\ce{C6H5NHCOCH3}$) may be effected by use of acetyl chloride or acetic anhydride or ketene. A transformation is distinct from a reaction, the full description of which would state or imply all the reactants and all the products.