The Terminology of Retrosynthesis

Each precursor molecule is also a target molecule. In terms of structural complexity, then, A 4 3 2 1 T. In each reverse step, we imagine how a bond can break to give two fragments this is called a bond disconnection. Disconnection for any bond X—Y can occur in three ways, as shown below. 

We have discussed many reactions that convert one functional group to another. In the terminology of retrosynthesis, such a reaction is called a functional group interconversion (FGI). The synthesis of a Grignard reagent from an benzyl bromide is an example. 

---