Q.How are the following conversions effected?

Step 1. (a) PROPANAL TO BUTANONE: propanal (CH3CH2CHO) + CH3MgBr (dry ether), then H3O+, undergoes Grignard addition to the aldehyde, giving the SECONDARY alcohol butan-2-ol, CH3CH2CH(OH)CH3 (an aldehyde + RMgX always gives a secondary alcohol); this secondary alcohol is then oxidised (K2Cr2O7/H+ or PCC) to the ketone, butanone (butan-2-one), CH3CH2COCH3.

Step 2. (b) HEX-3-YNE TO HEXAN-3-ONE: hex-3-yne, CH3CH2-C#C-CH2CH3, a symmetric INTERNAL alkyne, is hydrated directly with dilute H2SO4/HgSO4 (Section 12.3.A.3) -- Markovnikov addition of water across the internal triple bond, via an enol that tautomerises, gives the single ketone hexan-3-one, CH3CH2-CO-CH2CH2CH3, directly in ONE step (no separate oxidation needed, unlike route (a), since alkyne hydration installs the carbonyl immediately).

Step 3. (c) PHENYLMETHANAL TO BENZOIC ACID: phenylmethanal (benzaldehyde), oxidised with acidified K2Cr2O7 or KMnO4 (Section 12.5.B.1), gives benzoic acid directly, in a single straightforward oxidation step. …

Match each target product to the shortest named route already taught in the chapter -- a one-carbon-homologated methyl ketone from an aldehyde needs Grignard-then-oxidation, but a keto …

• Trying to make hexan-3-one via a Grignard-plus-oxidation detour (as in route (a)) instead of recognising that hex-3-yne's OWN internal-alkyne hydration installs the ketone directly in one step -- picking the unnecessarily …