Let's solve each part step by step: --- ## (a) Reaction Conditions for Conversion **Question:** Select the reaction condition(s) that could convert **2-methyl-2-butene** into **2-methyl-1,3-butadiene**. ### **Step-by-step Explanation:** - To convert an alkene (2-methyl-2-butene) into a conjugated diene (2-methyl-1,3-butadiene), you need to: 1. **Allylic bromination**: Introduce a bromine atom at the allylic position using NBS (N-bromosuccinimide) with light. 2. **Elimination**: Treat the allylic bromide with a strong base (EtONa/EtOH) and heat to generate the conjugated diene. **Correct answer is:** - (3) **NBS, light then EtONa/EtOH, heat** **Final Answer for (a):** - The correct reaction condition is: **(3) NBS, light (2) EtONa/EtOH, heat** --- ## (b) Retrosynthetic Scheme **Step-by-step Explanation:** - The target alkene has two cyano groups and two phenyl groups attached to a central double bond. - The precursor is a bromide attached to a methyl group (see scheme). - The retrosynthetic step involves an **E2 elimination** of the bromide (using a strong base) to form the alkene. **Retrosynthetic arrow should indicate:** - The bromide precursor can be converted to the target alkene using a base (such as NaOEt, NaOH, etc.). ### **Retrosynthetic Scheme:** ``` Target alkene: (C₆H₅)CH=C(CN)-C(CN)=C(C₆H₅)₂ ↑ (Base-induced elimination, Y = Br, Cl, or OH) Bromide precursor: (C₆H₅)CHBr-C(CN)-C(CN)=C(C₆H₅)₂ ``` --- ## (c) Diels–Alder Adduct Structure **Step-by-step Explanation:** - Diene: **2-methyl-1,3-butadiene** (isoprene) - Dienophile: The target alkene from (b), which is an electron-deficient alkene due to the cyano groups. ### **Diels–Alder Adduct:** - The Diels–Alder reaction forms a **six-membered ring**. - The new adduct will have the phenyl and cyano substituents at the positions introduced by the dienophile. **Structure:** Draw a six-membered cyclohexene ring with substituents: - Two cyano groups and two phenyl groups at the positions corresponding to the original dienophile. - The isoprene (2-methyl-1,3-butadiene) will add such that the methyl group is at the 4-position of the ring. --- ## **Summary Table** | Part | Answer/Explanation | |------|----------------------------------------------------------------------------------------------------| | (a) | (3) NBS, light (2) EtONa/EtOH, heat | | (b) | Retrosynthetic step: Elimination (base) from bromide precursor to form target alkene | | (c) | Diels–Alder adduct: six-membered ring with two cyano and two phenyl groups, plus a methyl at C-4 | --- ### **(a) Final Answer** > **(3) NBS, light (2) EtONa/EtOH, heat** ### **(b) Final Answer** > The retrosynthetic step is an **elimination** (using base) from the bromide precursor: > `(C₆H₅)CHBr-C(CN)-C(CN)=C(C₆H₅)₂ --(base)--> (C₆H₅)CH=C(CN)-C(CN)=C(C₆H₅)₂` ### **(c) Final Answer** > The Diels–Alder adduct is a cyclohexene derivative where the ring has: > - Two phenyl and two cyano substituents (from the dienophile) > - A methyl group (from the 2-methyl-1,3-butadiene) >  > *(This is a representative structure; you can draw it in standard cyclohexene form with substituents at appropriate positions.)* --- Let me know if you need the drawn structures or more details for part (c)!