Darzen's process.

Explanation

### Step-by-Step Solution for Darzen's Process

**Step 1: Understanding the Reactants**
- The main reactants in Darzen's process are an alcohol (ROH) and thionyl chloride (SOCl2).
- Alcohols are organic compounds containing a hydroxyl (-OH) group, while thionyl chloride is a reagent used to convert alcohols into alkyl halides.

**Step 2: Reaction Mechanism**
- When an alcohol reacts with thionyl chloride, the hydroxyl group (-OH) of the alcohol is replaced by a chlorine atom (Cl).
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