See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the substrate: The starting material is pent-4-en-1-ol (CH2=CH-CH2-CH2-CH2-OH), a terminal alkene with a hydroxyl group at the other end of a five-carbon chain. Step 2 - Reaction conditions: Br2 in H2O generates a bromonium ion intermediate at the double bond (C1-C2 of the alkene). Step 3 - Intramolecular vs intermolecular nucleophile: The pendant -OH group at C5 is perfectly positioned to form a five-membered ring by attacking the bromonium ion intramolecularly. A five-membered cyclic oxonium/tetrahydrofuran ring (tetrahydrofuran = THF) is highly favored by Baldwin's rules (5-exo-tet). The oxygen attacks the more electrophilic (less hindered terminal) carbon of the bromonium ion. Step 4 - Stereochemical outcome: The bromonium ion is attacked from the back face (anti addition). The oxygen of the -OH attacks the terminal carbon (C1) of the bromonium ion from the back, displacing Br- in an SN2-like fashion. This gives anti addition across the double bond, yielding a tetrahydrofuran ring with the -CH2Br group at C2 of the ring and the ring oxygen at C1, with anti (trans) stereochemistry between H and CH2Br at the ring junction carbon. Step 5 - Product identity: Because the bromonium ion is achiral (symmetric plane considerations) and forms on both faces of the alkene equally, two enantiomeric tetrahydrofuran products are obtained: one where CH2Br is on the wedge and H is on the dash (structure v), and one where CH2Br is on the dash and H is on the wedge (structure vi). These are the two enantiomers of 2-(bromomethyl)tetrahydrofuran formed via anti cyclization. Step 6 - Why other options fail: Options (i) and (ii) would require water acting as the external nucleophile to give a bromohydrin. While possible intermolecularly, the intramolecular cyclization to a 5-membered ring is strongly preferred (faster intramolecular reaction). Options (iii) and (iv) represent open-chain bromohydrins with incorrect regiochemistry. The cyclic ether products (v) and (vi) are the major products. Therefore, the correct answer is C.