# Synthesis Explanation ## Problem Recap **Starting materials:** - Cyclohexene (a 6-membered ring with one double bond) - Isobutene (2-methylpropene, (CH₂=C(CH₃)₂)) **Product:** - Cyclohexane ring with a sec-butyl group (–CH(CH₃)CH₂CH₃) attached ## Analysis ### 1. **Recognize the Reaction Type** This transformation requires joining cyclohexene and isobutene such that the isobutyl group is added to the cyclohexane ring. This is a classic **alkylation** reaction. ### 2. **Key Principle** - All carbons in the product must come from the starting materials. - The product shows the isobutyl group (from isobutene) attached to the cyclohexane ring. ### 3. **Possible Reactions** The most straightforward route is **alkylation via carbocation formation**: - Generate a carbocation from isobutene - Add it to cyclohexene But cyclohexene is not nucleophilic enough for direct alkylation. Instead, convert cyclohexene to a nucleophile (e.g., via **hydroboration-oxidation to cyclohexanol, then dehydration to cyclohexene, then further to a cyclohexyl halide or Grignard**). But, **Friedel–Crafts alkylation** is not possible directly on cyclohexene, but we can use an **acid-catalyzed alkylation** or a **radical addition** (Markovnikov addition of isobutene to cyclohexene). ### 4. **Stepwise Synthesis** #### **Step 1: Electrophilic Addition of Isobutene to Cyclohexene (Carbocation Mechanism)** **a. Generate tert-butyl carbocation from isobutene:** - Use acid (H⁺) to protonate isobutene, forming a tertiary carbocation. **b. Electrophilic addition to cyclohexene:** - The double bond of cyclohexene attacks the carbocation, forming a new C–C bond at the more substituted position (Markovnikov addition). #### **Step 2: Hydrogenation (if needed)** - If the product still contains a double bond, hydrogenate using H₂/Pd-C to get cyclohexane. --- ## **Detailed Mechanism** ### **Step 1: Carbocation Formation** - Isobutene + H⁺ → tert-butyl carbocation ### **Step 2: Alkylation** - Cyclohexene double bond attacks the carbocation at the more substituted position. - This gives a cyclohexyl ring with a sec-butyl substituent (after rearrangement, if necessary). ### **Step 3: Hydrogenation** - If any double bond remains, use H₂/Pd-C to fully saturate. --- ## **Reagents Needed** 1. **Acid (H₂SO₄ or H₃PO₄)** to generate carbocation from isobutene 2. **H₂ / Pd-C** for hydrogenation --- ## **Summary of Steps** 1. **Mix cyclohexene and isobutene with strong acid:** - The isobutene is protonated to give a carbocation. - Cyclohexene’s double bond attacks the carbocation, forming a new C–C bond. 2. **Hydrogenate if necessary (H₂, Pd-C):** - Reduces any remaining double bond, giving a fully saturated product. --- ## **Handwritten Work Example (Structure Flow)** ```plaintext Cyclohexene Isobutene ⬇ ⬇ [H⁺] → Carbocation ⬇ Double bond of cyclohexene attacks carbocation ⬇ Cyclohexyl-sec-butyl intermediate (may still have a double bond) ⬇ [H₂, Pd-C] ⬇ Final Product: sec-butyl cyclohexane ``` --- ## **Tips** - Pay attention to **Markovnikov selectivity** (the more stable carbocation will form). - All carbons in the product are accounted for from the starting materials. --- **If you need a fully handwritten version, you should draw each step as described above, showing the movement of electrons and the intermediate structures.** Let me know if you want a stepwise drawing or further breakdown!