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JEE Main levelSingle correct optionDifficulty 2 of 3o4078

In ethanol with no added base, 2-bromo-2-methylpropane gives an ether (SN1) and an alkene (E1) through the same carbocation. On raising the temperature the fraction of alkene increases because

  1. Athe ionisation step of E1 is faster than that of SN1
  2. Bethanol evaporates and the ether product is lost
  3. Celimination has a higher activation energy than substitution, so its rate constant rises faster with temperature
  4. DE1 and SN1 have different rate-determining steps, and only that of E1 speeds up

Answer: C

Both products arise from the same rate-determining ionisation, so a change in its rate cannot change their ratio. The ratio changes only if the activation energies differ. Elimination has the larger activation energy (and a more favourable entropy change), so increases with temperature.
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