See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Step 1 - Reaction Concept: NBS (N-bromosuccinimide) in aqueous DMSO acts as a source of Br+ (electrophilic bromine) and water acts as a nucleophile. This is a bromohydrin-type reaction (halohydrin formation) on the double bond of 1-methylcyclohexene, NOT allylic bromination (which would require non-aqueous, radical conditions with light/heat). Step 2 - Mechanism: NBS in aqueous solvent generates Br+ which attacks the alkene of 1-methylcyclohexene to form a bromonium ion intermediate. The bromonium ion forms on the double bond (C1-C2 of the ring, where C1 bears the methyl group). Water then attacks the more substituted carbon (C1, which bears the methyl group) from the back (anti addition) as the nucleophile, while Br is delivered to C2. Step 3 - Regiochemistry: Following Markovnikov selectivity, the OH (from water) ends up on the more substituted carbon (C1, bearing methyl), and Br ends up on C2. Step 4 - Stereochemistry: The bromonium ion intermediate enforces anti addition. This means OH and Br add from opposite faces of the double bond. The product is trans-2-bromo-1-methylcyclohexan-1-ol, meaning OH (at C1) and Br (at C2) are trans to each other (anti relationship). Since C1 also bears the methyl group, at C1 we have OH and Me. The product shows OH on wedge and Br on dash (or vice versa) indicating anti addition across the ring. Step 5 - Evaluating options: - Option (a) shows allylic bromination product (Br at C3 of cyclohexene), which is wrong for aqueous DMSO conditions. - Option (b) shows cyclohexane with OH (wedge) at C1, Me (wedge) at C1, and Br (dash) at C2. This represents OH and Br in a trans (anti) relationship - OH on one face, Br on opposite face - consistent with anti addition via bromonium ion. This is the correct bromohydrin with proper anti stereochemistry. - Option (c) shows OH (wedge) at C1 and Br (wedge/bold) at C2, meaning both on the same face - this would be syn addition, which is inconsistent with bromonium ion mechanism. - Option (d) is eliminated since (b) is correct. Step 6 - Conclusion: Option (b) correctly shows the bromohydrin product of 1-methylcyclohexene with NBS/aqueous DMSO, with anti addition stereochemistry (OH and Br trans to each other). Therefore, the correct answer is B.