Retrosynthetic analysis is a technique for solving problems in the planning of organic syntheses. This is achieved by transforming a target molecule into simpler precursor structures regardless of any potential reactivity/interaction with reagents. Each precursor material is examined using the same method. This procedure is repeated until simple or commercially available structures are reached. These simpler/commercially available compounds can be used to form a synthesis of the target molecule. E.J. Corey formalized this concept in his book The Logic of Chemical Synthesis. The power of retrosynthetic analysis becomes evident in the design of a synthesis. The goal of retrosynthetic analysis is a structural simplification. Often, a synthesis will have more than one possible synthetic route. Retrosynthesis is well suited for discovering different synthetic routes and comparing them in a logical and straightforward fashion. A database may be consulted at each stage of the analysis, to determine whether a component already exists in the literature. In that case, no further exploration of that compound would be required. If that compound exists, it can be a jumping point for further steps developed to reach a synthesis. Definitions Disconnection A retrosynthetic step involving the breaking of a bond to form two (or more) synthons. Retron A minimal molecular substructure that enables certain transformations. Retrosynthetic tree A directed acyclic graph of several (or all) possible retrosyntheses of a single target. Synthon A fragment of a compound that assists in the formation of a synthesis, derived from that target molecule. A synthon and the corresponding commercially available synthetic equivalent are shown below: Target The desired final compound. Transform The reverse of a synthetic reaction; the formation of starting materials from a single product. Example An example will allow the concept of retrosynthetic analysis to be easily understood. In planning the synthesis of phenylacetic acid, two synthons are identified. A nucleophilic "-COOH" group, and an electrophilic "PhCH2+" group. Of course, both synthons do not exist per se; synthetic equivalents corresponding to the synthons are reacted to produce the desired product. In this case, the cyanide anion is the synthetic equivalent for the −COOH synthon, while benzyl bromide is the synthetic equivalent for the benzyl synthon. The synthesis of phenylacetic acid determined by retrosynthetic analysis is thus: PhCH2Br + NaCN → PhCH2CN + NaBr PhCH2CN + 2 H2O → PhCH2COOH + NH3 In fact, phenylacetic acid has been synthesized from benzyl cyanide, itself prepared by the analogous