See image — Haloalkanes and Haloarenes Chemistry Question

💡 Solution & Explanation

Concept: SN1 and SN2 reactions have opposite dependence on substrate structure. SN1 rate depends on carbocation stability (tertiary > secondary > primary > methyl), while SN2 rate depends on steric accessibility (methyl > primary > secondary > tertiary). Step 1 - Identify each substrate: (a) CH3-Br = methyl bromide (methyl) (b) CH3-CH2-Br = ethyl bromide (primary) (c) CH3-CH(CH3)-Br = isopropyl bromide (secondary) (d) CH3-C(CH3)2-Br = tert-butyl bromide (tertiary) Step 2 - Match SN1 relative rates (carbocation stability order: methyl << primary << secondary << tertiary): - Methyl (a): essentially no SN1, relative rate ~ 1 → matches (p) 1 - Primary (b): very slow SN1, relative rate ~ 1.05 → matches (q) 1.05 - Secondary (c): moderate SN1, relative rate ~ 11 → matches (r) 11 - Tertiary (d): very fast SN1, relative rate ~ 1,200,000 → matches (s) 1,200,000 Step 3 - Match SN2 relative rates (steric hindrance order: methyl > primary > secondary > tertiary): - Methyl (a): least hindered, fastest SN2, relative rate ~ 1200 → matches (w) 1200 - Primary (b): slightly hindered, relative rate ~ 40 → matches (x) 40 - Secondary (c): more hindered, relative rate ~ 16 → matches (y) 16 - Tertiary (d): most hindered, essentially no SN2, relative rate ~ 1 → matches (z) 1 Step 4 - Verify: The trends are internally consistent. As substitution increases from methyl to tertiary, SN1 rate increases dramatically (1 to 1,200,000) while SN2 rate decreases dramatically (1200 to 1). No other assignment satisfies both trends simultaneously. Therefore, the correct answer is {"A": ["P", "W"], "B": ["Q", "X"], "C": ["R", "Y"], "D": ["S", "Z"]}.