See image — Alcohols Phenols and Ethers Chemistry Question

💡 Solution & Explanation

Concept: Converting a secondary alcohol to an alkyl bromide requires a reagent that substitutes the -OH group with -Br without causing rearrangement or side reactions, and does so cleanly and efficiently. Step 1: Evaluate each reagent. - HBr (option a): HBr can convert alcohols to alkyl bromides via an SN1 or SN2 mechanism. For secondary alcohols, it works but can lead to rearrangements and gives lower yields; also requires harsh conditions or a catalyst. - SOBr2 (option b): Thionyl bromide (SOBr2) reacts with alcohols to form an alkyl bromosulfite intermediate, which then undergoes displacement to give the alkyl bromide with release of SO2 and HBr as gaseous byproducts. This reaction proceeds cleanly, gives high yields, and the byproducts (SO2 and HBr gas) are easily removed, making the product pure. It is analogous to the well-known SOCl2 reaction for making alkyl chlorides. - Br2 (option c): Molecular bromine is used for addition to alkenes or electrophilic aromatic substitution, not for converting alcohols to alkyl bromides. - CH3MgBr (option d): A Grignard reagent is a nucleophile/base and would react with the alcohol's O-H bond (proton transfer), not substitute the OH group. Step 2: Identify the best reagent. SOBr2 is the best reagent because it converts the alcohol to the alkyl bromide via a clean mechanism with gaseous byproducts (SO2 and HBr), giving a pure product in high yield without rearrangement issues. Step 3: Why other options fail: - HBr can work but is less clean and may cause rearrangements with secondary alcohols. - Br2 does not react with alcohols to give alkyl bromides under normal conditions. - CH3MgBr simply deprotonates the alcohol. Therefore, the correct answer is B.