$word_{count}$: 200

JEE frequently tests multi-step synthesis involving carbonyl chemistry. Key strategic tools: Chain extension: Grignard + C=O (add R group), HCN addition (add CN → hydrolyze to COOH), Wittig (specific C=C placement), Arndt-Eistert (homologation by one CH2), malonic/acetoacetic ester synthesis $\frac{build substituted acids}{ketones}$. Chain reduction: soda-lime decarboxylation (lose one C), Hunsdiecker (RCOOH → RBr, lose one C), Hofmann degradation (RCONH2 → RNH2, lose one C). Functional group interconversion: PCC oxidation (alcohol → aldehyde), Jones (alcohol → acid), Grignard + CO2 (halide → acid), NaBH4 (C=O → alcohol), Clemmensen/Wolff-Kishner (C=O → CH2). When planning synthesis: work backward from target (retrosynthetic analysis), identify C-C bond disconnections (Grignard, aldol, Wittig are the main C-C forming reactions), and protect sensitive groups (acetals for C=O protection, stable in base, removed by acid). Always check: does the substrate have alpha-H $\frac{aldol}{enolate chemistry}$ or not $\frac{Cannizzaro}{Wittig}$?