Chemical synthesis is the deliberate preparation of a chemical substance from other substances through one or more controlled chemical reactions. A synthesis specifies starting materials, transformations, reaction conditions, and an isolation sequence that establishes the constitution and, when relevant, stereochemistry of the product. In multistep synthesis, intermediates are connected by an ordered route in which bond formation, bond cleavage, functional-group interconversion, and stereochemical control progressively produce the target structure. The concept includes small-molecule, macromolecular, and biomolecular construction when assembly occurs through chemically executed reactions; total chemical synthesis of proteins, for example, forms peptide segments and joins them by chemical ligation ^[1]. Parallel chemical synthesis applies the same criterion through repeated, spatially addressed reaction cycles ^[2]. Chemical synthesis is distinct from isolation of an existing substance, purely physical mixing or self-assembly without covalent transformation, and biosynthesis executed by a living organism's metabolic machinery.