## Step-by Mechanism for the Transformation ###Question Recap** - **Starting material:** 2-butanol (CH₃CH(OH)CH₂CH₃) - **Reagent:** HBr - **Product:** 2-bromobutane (CH₃CH(Br)CH₂CH₃) --- ## **Step 1: Protonation of Alcohol & Formation of Good Leaving Group** 1. **The -OH group of the alcohol is protonated by HBr:** - The oxygen of the alcohol donates a lone pair to a **proton (H⁺)** from HBr, forming water (a good leaving group). 2. **Water (H₂O) leaves, forming a carbocation intermediate:** - The water molecule leaves, generating a **secondary carbocation** at the second carbon. **Explanation:** Alcohols are poor leaving groups, but after protonation, -OH becomes H₂O, which is a much better leaving group. The departure of water generates a more stable carbocation (secondary in this case). --- ## **Step 2: Nucleophilic Attack by Bromide Ion** 1. **Br⁻ ion attacks the carbocation:** - The bromide ion (Br⁻), generated from HBr, quickly attacks the carbocation center, forming the final product. **Explanation:** The carbocation formed in step 1 is highly reactive and immediately gets attacked by the nucleophilic Br⁻, leading to the formation of 2-bromobutane. --- ## **Final Answer** **Mechanism Summary:** 1. **Protonation of alcohol and loss of water to form a carbocation.** 2. **Nucleophilic attack by Br⁻ on the carbocation to give 2-bromobutane.** This is an example of an **SN1 reaction mechanism** (unimolecular nucleophilic substitution).