Let's analyze the reaction step by step: ### 1. **Identify the starting compound** - The molecule is a **benzoin** derivative: it is **benzyl phenyl ketone** (benzoin). - Structure: Two benzene rings attached to a carbon (benzylic position), which is also attached to a carbonyl group (CO). ### 2. **Reagent: HBr** - HBr is a strong acid and a source of Br⁻. ### 3. **Possible Reactions** - In the presence of HBr, alpha-bromination of a carbonyl compound can occur (the alpha carbon is the one next to the carbonyl group). - The benzylic position (the carbon attached to both rings) is particularly reactive to substitution, especially under acidic conditions. ### 4. **Mechanism** - **Enolization:** The carbonyl compound can tautomerize to its enol form under acidic conditions. - **Bromination:** The enol form reacts with Br⁻ (from HBr) to substitute a hydrogen at the alpha position with a Br atom. ### 5. **Step-by-Step Mechanism** #### Step 1: Protonation of the Carbonyl Oxygen - The carbonyl oxygen is protonated by HBr, increasing electrophilicity. #### Step 2: Enol Formation - The alpha hydrogen (at the benzylic position) is somewhat acidic and is lost (enol formation). #### Step 3: Electrophilic Bromination - The enol attacks Br₂ (generated in situ from HBr oxidation), or HBr can provide Br⁺ under acidic conditions. - The bromine attaches to the alpha-carbon (the carbon attached to both rings). ### 6. **Product** The bromine atom replaces one of the hydrogens at the benzylic (alpha) position: **Product structure:** - The central carbon has a Br, a phenyl group, a benzene ring, and a carbonyl group. **Drawn structure:** ``` Br | Ph—C—CO—CH₃ | Ph ``` But since there is no methyl, let's redraw: - The structure will be: Benzene—C(Br)(Ph)—CO—H But the original molecule is benzoin (Ph-CHOH-CO-Ph), so after bromination: - The alpha carbon (benzylic) gets a Br. **Final product:** - **α-Bromo-benzoin** (or α-bromo-diphenylacetone): Two benzene rings on a central carbon, which bears a Br and a COCH₃ group. - **Structure:** ``` Br | Ph—C—CO—Ph | Ph ``` ### **Final Answer:** The product is **α-bromo-benzoin** (α-bromo-diphenylacetone): ``` Br | Ph—C—CO—Ph | Ph ``` Where the Br is attached to the alpha carbon (the central carbon), which is also attached to two phenyl groups and a carbonyl group.