Order of **dehydration rate** of alcohols R-CH₂-OH, R₂-CHOH, R₃-COH (R = CH₃) with conc. H₂SO₄ is:
A1° > 2° > 3°
B3° > 2° > 1° (E1 mechanism, more stable cation = faster)
C2° > 3° > 1°
DAll equal
Answer & Solution
Correct answer: B. 3° > 2° > 1° (E1 mechanism, more stable cation = faster)
E1 dehydration rate ∝ carbocation stability. 3° alcohol → 3° carbocation (most stable) → fastest. Conditions: 3° at 20%H₂SO₄, 85 °C; 2° at 60%, 100 °C; 1° at 95%, 170 °C.
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