### Core Logic Let's match each aldehyde preparation method with its official named organic reaction: * **(A) mathrmRCN ightarrow mathrmRCHO$\mathrm{RCN} ightarrow \mathrm{RCHO}$ using mathrmSnCl_2/mathrmHCl$\mathrm{SnCl}_{2}/\mathrm{HCl}$ followed by hydrolysis:** This is the classic **Stephen reaction** ightarrow$ ightarrow$ **(IV)**. * **(B) Reducing an acyl chloride (mathrmRCOCl$\mathrm{RCOCl}$) to an aldehyde using mathrmH_2$\mathrm{H}_{2}$ over mathrmPd-BaSO_4$\mathrm{Pd-BaSO}_{4}$:** This partial reduction is known as the **Rosenmund reduction** ightarrow$ ightarrow$ **(III)**. * **(C) Oxidizing toluene to benzaldehyde using chromyl chloride (mathrmCrO_2mathrmCl_2$\mathrm{CrO}_{2}\mathrm{Cl}_{2}$) in mathrmCS_2$\mathrm{CS}_{2}$:** This selective oxidation method is the **Etard reaction** ightarrow$ ightarrow$ **(I)**. * **(D) Converting benzene to benzaldehyde using mathrmCO$\mathrm{CO}$ and mathrmHCl$\mathrm{HCl}$ in the presence of anhydrous mathrmAlCl_3/mathrmCuCl$\mathrm{AlCl}_{3}/\mathrm{CuCl}$:** This formylation process is the **Gatterman-Koch reaction** ightarrow$ ightarrow$ **(II)**. Combining these assignments yields the final sequence: (A)-(IV), (B)-(III), (C)-(I), (D)-(II). ### Step-by-Step Layout The visual reaction components correspond directly to the official structural transformations:

### Pattern Recognition Quick identification keys: - Nitrile ightarrow$ ightarrow$ Aldehyde = Stephen - Acid Chloride ightarrow$ ightarrow$ Aldehyde = Rosenmund - Toluene ightarrow$ ightarrow$ Chromyl Complex = Etard - Benzene ightarrow$ ightarrow$ Carbon Monoxide = Gatterman-Koch ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Chemistry: Aldehydes, Ketones and Carboxylic Acids