Let's tackle each problem step by step, providing explanations and final answers. --- # 1. Predict the products and provide step-by-step mechanisms ## (a) **Reaction:** Benzene + HCl (gas) in benzene **Explanation:** Benzene does **not** react with HCl under these conditions because HCl is not a strong enough electrophile to react with aromatic rings. No Friedel-Crafts catalyst (like AlCl₃) is present. **Product:** No reaction. --- ## (b) **Reaction:** 2-methylbut-2-ene + cat. HCl in methanol (CH₃OH) **Mechanism:** 1. **Protonation of Alkene**: The double bond attacks H⁺, forming a carbocation at the more substituted carbon (Markovnikov addition). 2. **Nucleophilic Attack**: Methanol attacks the carbocation. 3. **Deprotonation**: Methanol loses a proton to form the ether. **Product:** 2-chloro-2-methylbutane - If a new stereocenter is formed, a racemic mixture results. --- ## (c) **Reaction:** Cyclohexene + HBr (gas) in inert solvent (dry toluene) **Mechanism:** 1. **Protonation of double bond** to form the most stable carbocation (Markovnikov). 2. **Br⁻ attacks carbocation.** **Product:** Bromocyclohexane --- ## (d) **Reaction:** 1-butene + HBr (gas) in toluene **Mechanism:** 1. **Protonation** of the double bond (Markovnikov). 2. **Br⁻ attacks the carbocation.** **Product:** 2-bromobutane (racemic mixture, since a new chiral center is formed at C2). --- ## (e) **Reaction:** Benzene + HCl (gas) in dry toluene **Explanation:** Just like part (a), benzene does **not** react with HCl without a Lewis acid catalyst. **Product:** No reaction. --- ## (f) **Reaction:** 1-pentene + cat. HCl (g) in methanol (CH₃OH) **Mechanism:** 1. **Protonation** of the double bond (Markovnikov). 2. **Methanol attacks the carbocation.** 3. **Deprotonation** leads to the ether. **Product:** 2-methoxypentane (racemic mixture if a new chiral center is formed). --- # 2. Carbocation Stability Draw hydrogens and rank from least to most stable. - **A:** Cyclopropyl carbocation (least stable, high ring strain, poor overlap) - **B:** Cyclopentyl carbocation - **C:** Cyclohexyl carbocation - **D:** Cycloheptyl carbocation - **E:** Benzyl carbocation (most stable, resonance stabilization) **Ranking (least to most stable):** A < B < C < D < E - **Resonance structure for E:** Positive charge delocalized on the aromatic ring. --- # 3. Ring Formation Mechanism **(a) Mechanism:** 1. **Protonation** of the alcohol by HCl makes a good leaving group (water). 2. **Intramolecular nucleophilic attack**: The terminal carbon attacks the carbocation, forming a ring. 3. **Deprotonation** to form the final product. **Product:** Tetrahydrofuran (THF) ring structure. --- **(b) Is the final product achiral, racemic, or one enantiomer?** - The product is **achiral** because tetrahydrofuran is a symmetric ring with no chiral centers formed during the reaction. --- # **Summary Table** | Part | Product | Racemic? | Comments | |------|---------|----------|----------| | 1a | No rxn | - | Benzene inert to HCl without catalyst | | 1b | 2-chloro-2-methylbutane | Possibly racemic | If chiral center forms | | 1c | Bromocyclohexane | No | | | 1d | 2-bromobutane | Racemic | New chiral center | | 1e | No rxn | - | | | 1f | 2-methoxypentane | Racemic | New chiral center | | 2 | E > D > C > B > A | - | Carbocation stability | | 3a | Tetrahydrofuran | Achiral | | | 3b | Achiral | - | | --- If you need step-by-step arrow-pushing mechanisms for any part or resonance structures, let me know!