21.1.2—Devise multi-step synthetic routes

A multi-step synthesis is a sequence of reactions that changes one functional group or carbon skeleton at a time. Work backward from the target to choose a plausible immediate precursor, then reverse the route to check reagents and conditions.

Track carbon count, oxidation state and functional-group compatibility after every step. Prefer the shortest syllabus-supported route and separate preparation from purification.

To make propanoic acid from 1-bromopropane: substitution with CN⁻ gives propanenitrile, then hydrolysis and acidification gives propanoic acid.

Do not propose a reagent that changes the carbon count accidentally, and do not omit conditions such as reflux, catalyst or acid work-up.