# Explain why propene reacts with concentrated sulfuric acid to form propan-2-yl hydrogensulfate as the major product rather than propan-1-yl hydrogensulfate.

> IB DP Chemistry Higher Level (2023 syllabus) — R3.3 Electron sharing reactions · Explain · 4 marks

## Mark scheme (4 marks)

1. The π electrons of propene act as a nucleophile and attack the electrophilic hydrogen of H₂SO₄, forming a carbocation intermediate.
2. Protonation at C-1 gives a secondary carbocation at C-2, whereas protonation at C-2 gives a primary carbocation at C-1.
3. The secondary carbocation is more stable than the primary carbocation due to greater inductive electron-donating effect of the additional alkyl group, which disperses the positive charge.
4. The hydrogensulfate ion (HSO₄⁻) then attacks the more stable secondary carbocation, yielding propan-2-yl hydrogensulfate as the major product (Markovnikov's rule / Markovnikov addition).

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