Since A effervesces when added to a solution of sodium hydrogen carbonate it is probably a carboxylic acid. It reacts immediately with bromine water in an addition reaction since the difference between C₉H₈O₂ and C₉H₈O₂Br₂ is a bromine molecule. A therefore probably contains a C=C double bond. The relatively large carbon:hydrogen ratio suggests that the compounds contain a benzene ring – long chains of double bonds are unlikely. The existence of stereoisomerism means that the C=C bond has one group(s) other than hydrogen on each carbon atom. This leads to the conclusion that A is probably C₆H₅CH=CHCOOH, cinnamic acid, and B the dibromo derivative:

C₆H₅CH=CHCOOH + Br₂ à C₆H₅CH(Br)CH(Br)COOH

The reaction is electrophilic addition.

With aqueous sodium hydroxide solution B is both neutralised and undergoes nucleophilic substitution:

C₆H₅CH(Br)CH(Br)COOH + 3NaOH à C₆H₅CH(OH)CH(OH)COONa + 2NaBr + H₂O

C is therefore C₆H₅CH(OH)CH(OH)COOH, mandelic acid. This compound can be oxidised by acidified potassium dichromate solution to the diketone D:

C₆H₅CH(OH)CH(OH)COOH + 2[O] à C₆H₅COCOCOOH   +  2H₂O

D reacts with 2,4-dinitrophenylhydrazine but not with ammoniacal silver nitrate solution since ketones are not reducing agents. D gives steamy fumes with phosphorus pentachloride because of the –OH in the carboxyl group, the organic product being E, an acid chloride:

C₆H₅COCOCOOH + PCl₅ à C₆H₅COCOCOOCl + POCl₃ + HCl

With ammonia E gives F which is a nucleophilic substitution reaction:

C₆H₅COCOCOOCl + 2NH₃ à C₆H₅COCOCOONH₂ + NH₄Cl

Both F and A are oxidised by hot aqueous potassium manganate(VII) solution to the sodium salt of G; this is benzoic acid, C₆H₅COOH. As with all carbon-containing side chains in aromatic compounds, potassium manganate(VII) oxidatively cleaves these to leave one carbon atom attached to the ring.

Mass spectrum:

Infrared spectrum:

Proton magnetic resonance spectrum: