See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Step 1: Identify the structure. The compound is CH3-CH=CH-CH(Br)-CH(Cl)-CH3, which is 4-bromo-5-chlorohex-2-ene. Step 2: Identify stereocentres. A stereocentre (stereogenic centre) is any element that, when its groups are interchanged, produces a stereoisomer. This includes both chiral centres (sp3 carbons with 4 different groups) and the carbons of a C=C double bond that give rise to geometric (E/Z) isomerism. Step 3: Analyse the double bond (C2=C3). C2 has groups: CH3 and the rest of the chain (=CH-). C3 has groups: H and the rest of the chain. Both carbons of the double bond bear two different substituents each, so the double bond is capable of E/Z isomerism. Each carbon of a geometrically restricted double bond counts as a stereocentre. Therefore C2 and C3 each contribute 1 stereocentre, giving 2 stereocentres from the double bond. Step 4: Analyse C4 (CH with Br). Its four substituents are: Br, H, -CH=CH-CH3 (the alkenyl chain), and -CH(Cl)-CH3. All four are different, so C4 is a chiral centre (1 stereocentre). Step 5: Analyse C5 (CH with Cl). Its four substituents are: Cl, H, -CH(Br)-CH=CH-CH3 (the chain toward C4), and -CH3. All four are different, so C5 is a chiral centre (1 stereocentre). Step 6: Total stereocentres = 2 (from C=C, E/Z) + 1 (C4) + 1 (C5) = 4. Therefore, the correct answer is 4.