# Stepwise Synthesis Explanation Let's analyze and solve the problem step by step. ## **Given:** - **Starting Material:** 2-butane (sec-butane) - **Target:** 2-bromo-3-methylbutane (racemic mixture) --- ## **Step 1: Bromination to Introduce a Leaving Group** You need to add a functional group to the molecule that can be substituted by Br at the desired position. ### **a. Bromination of Alkane** - **Reagent:** Br₂, hv (light) - **Reaction:** Free-radical bromination - **Major Product:** Bromination occurs at the more substituted carbon (the 2° carbon). **Product:** ``` Br | CH3-CH-CH2-CH3 ``` (2-bromobutane) --- ## **Step 2: Formation of an Alkene (Elimination)** You want to shift the position of the functional group from the 2-position to the 3-position. First, convert the bromoalkane to an alkene. ### **a. Elimination (E2)** - **Reagent:** NaOEt (sodium ethoxide) in ethanol (EtOH) - **Reaction:** E2 elimination to form the more substituted alkene (Zaitsev's rule) **Product:** ``` CH3 | CH2=CH-CH-CH3 ``` (2-methyl-2-butene) --- ## **Step 3: Electrophilic Addition of HBr (Markovnikov)** Now, you want to add Br to the 3-position. ### **a. HBr Addition (Markovnikov)** - **Reagent:** HBr (no peroxides; normal Markovnikov addition) - **Reaction:** HBr adds across the double bond, Br attaches to the more substituted carbon (3-position) **Product:** ``` Br | CH3-CH-CH(CH3)-CH3 ``` (2-bromo-3-methylbutane, racemic mixture because a new chiral center forms) --- ## **Summary Table** | Step | Reaction Type | Reagents & Conditions | Product | |------|-------------------|-------------------------------|---------------------------------| | 1 | Radical bromination | Br₂, hv (light) | 2-bromobutane | | 2 | Elimination (E2) | NaOEt/EtOH, heat | 2-methyl-2-butene | | 3 | Electrophilic addition | HBr (no peroxides) | 2-bromo-3-methylbutane (±) | --- ## **Key Points** - The sequence uses selective bromination, elimination, and Markovnikov addition to access the target. - The product is racemic due to the creation of a new stereocenter. Let me know if you’d like a detailed mechanism or further clarification on any step!