Retrosynthesis (one Step Back)

Work backwards: the target's group came from a school precursor. Ethanoic acid <- ethanol <- ethene. Propanone <- propan-2-ol <- propene. A nitrile in the target might have come from a haloalkane + CN- (carbon chain grew). Disconnections in these notes are one functional group, not professional route design, not patent routes, not drugs. Target alcohol? Maybe reduction of carbonyl or hydration of alkene — pick allowed precursor. Count carbons after each synthetic step; silent carbon loss is the most common multi-step mistake.

RETROSYNTHESIS (ONE STEP BACK) is an independent FBISE learning unit because students must use its definitions, conditions, equations, or trends separately in explanations and calculations.

LAST STEP: If the target is an ester, last step is acid + alcohol. If an alkene, last step might be dehydration or elimination. Write the reagent with the arrow. One step back keeps planning manageable — full tree is university level. Examples: Esterify; Dehydrate; Eliminate. CHAIN LENGTH: Same carbons: ox/redox, add/elim, sub. Extra carbon: nitrile from CN- then hydrolyse. Never invent a Grignard unless the book taught it (name only if so). Ask: what functional group is one reaction before target? Examples: Ethene C2 stays C2 to ethanol; CN- C1 RX -> C2 nitrile; No extra methods. Worked back: ethyl ethanoate. last step: ethanol + ethanoic acid, H2SO4 ethanol from ethene hydration (named) ethanoic from ethanol oxidation