36. Organic synthesis

When a molecule contains multiple functional groups, identify each group first, then combine their reaction patterns without letting one group erase the others.

Check for competing conditions and selectivity: an aldehyde, alcohol, amine or carboxylic acid may each respond to different reagents, while steric and electronic effects can alter access.

An amino acid contains both –NH₂/–NH₃⁺ and –COOH/–COO⁻ chemistry, so it can act as an acid or base and form peptide bonds.

Do not assign one “overall functional group” to a multifunctional molecule; list the groups and test the reagent against each.

A synthetic route is a sequence of syllabus reactions that converts an available starting material into a target. Work backwards from the target group, choose a compatible precursor, then check that each reagent and condition is selective.

Record the transformation at every arrow and keep track of carbon count, oxidation state and side products. Shorter routes are not automatically better if they violate conditions.

To make an ester, choose a carboxylic acid plus alcohol (equilibrium route) or an acyl chloride plus alcohol (rapid route), then select how each precursor can be prepared.

A route is not justified by naming familiar reagents; every step must match a structural change and preserve the rest of the molecule.

For each step in a route, identify the functional-group change, classify the reaction, name the reagent/condition and note likely by-products.

Compare the structures before and after: oxidation changes bonding to oxygen, substitution replaces a leaving group, addition consumes a π bond, and condensation removes a small molecule.

Alcohol → aldehyde with acidified dichromate is oxidation; acyl chloride + alcohol → ester is nucleophilic acyl substitution with HCl formed.

Do not classify a reaction from the reagent alone; the same reagent can behave differently with different functional groups and conditions.