Dehydration of an alcohol (E1) template

2-Methylbutan-2-ol with hot concentrated acid: O-protonation, loss of water to the tertiary cation and loss of a β-H give 2-methylbut-2-ene (Zaitsev).

Mechanism step by step

Acid turns OH into a leaving group; the carbocation loses a β-proton to give the more substituted alkene

1. Protonation – OH becomes OH₂⁺, a good leaving group
2. Loss of water (slow) – A tertiary carbocation forms
3. Loss of a β-proton – Water takes H from CH₂: the trisubstituted alkene

Key points

• Zaitsev: losing H from CH₂ gives the more substituted, more stable alkene; 2-methylbut-1-ene is the minor product.
• Ease of dehydration: 3° > 2° > 1° alcohol (primary alcohols react by E2 at higher temperature).
• Distilling the alkene out as it forms pulls the equilibrium over; H₃PO₄ chars less than H₂SO₄.
• Carbocation rearrangements (hydride or methyl shifts) can change the carbon skeleton.

Drawn with 60 atoms, 9 arrows, 7 shapes – every one editable in MolDraw.

Sources

• Clayden, Greeves & Warren, Organic Chemistry, 2nd ed., OUP 2012, ch. 17 Textbook
• Smith, March's Advanced Organic Chemistry, 8th ed., Wiley 2020, ch. 17 Textbook