# Step-by-Step Solution ## **Step 1: Analyze the Starting Materials and Product** - **Starting materials:** - Cyclohexane (C₆H₁₂) - Isopropyl bromide (or isopropyl halide, (CH₃)₂CH−X) - **Product:** - Sec-butylcyclohexane (cyclohexane ring with a sec-butyl group attached) ## **Step 2: Identify the Reaction Type** This is a classic **Friedel–Crafts alkylation** reaction, where an alkyl halide reacts with an aromatic or, in this case, a cycloalkane (after activation) in the presence of a Lewis acid to form an alkylated product. However, since cyclohexane is not aromatic and does not undergo Friedel–Crafts directly, another mechanism must be considered: **free radical alkylation** or **nucleophilic substitution**. But, based on the product, an **alkylation** of cyclohexane with isopropyl halide is necessary. ## **Step 3: Mechanism Proposal** Since cyclohexane is not aromatic and cannot directly react in a Friedel–Crafts reaction, let's consider a **free radical alkylation** (Wurtz-type coupling) or **alkylation via carbocation**: ### **Step 3.1: Generation of Isopropyl Carbocation** Isopropyl halide can form a carbocation under strongly acidic or Lewis acidic conditions. ### **Step 3.2: Rearrangement to Sec-Butyl Carbocation** Isopropyl carbocation can hydride shift to form a more stable secondary butyl (sec-butyl) carbocation. ### **Step 3.3: Cyclohexane as Nucleophile** Cyclohexane can act as a nucleophile and attack the sec-butyl carbocation, leading to the formation of sec-butylcyclohexane. ## **Step 4: Write the Full Reaction** - **Reagents:** Cyclohexane + isopropyl halide (CH₃)₂CH−X + strong Lewis acid (e.g., AlCl₃) or radical initiator. ## **Step 5: Final Balanced Reaction** \[ \text{Cyclohexane} + \text{Isopropyl halide} \xrightarrow{\text{AlCl}_3} \text{sec-Butylcyclohexane} \] ## **Step 6: Mechanism** 1. **Formation of isopropyl carbocation:** \[ (CH_3)_2CH-X + \text{AlCl}_3 \rightarrow (CH_3)_2CH^+ + \text{AlCl}_4^- \] 2. **Hydride shift:** \[ (CH_3)_2CH^+ \rightarrow CH_3CH_2CH^+CH_3\ (\text{sec-butyl carbocation}) \] 3. **Attack by cyclohexane:** \[ \text{Cyclohexane} + \text{sec-butyl carbocation} \rightarrow \text{sec-butylcyclohexane} \] ## **Step 7: Final Answer** ### **Required Conditions** - **Reagent:** Isopropyl halide (e.g., isopropyl bromide or chloride) - **Cyclohexane** - **Strong Lewis acid (e.g., AlCl₃)** --- ## **Summary Table** | Reactant 1 | Reactant 2 | Reagent | Product | |---------------|--------------------|--------------|--------------------------| | Cyclohexane | Isopropyl halide | AlCl₃ | sec-Butylcyclohexane | --- ### **Final Answer:** **The missing reagent is a strong Lewis acid (such as AlCl₃), and the reaction is a Friedel–Crafts-type alkylation (with carbocation rearrangement) that results in sec-butylcyclohexane.** --- Let me know if you want a stepwise mechanism drawing!