Hydroboration–oxidation template

BH₃ adds H and B in one four-centre step, B on the less hindered carbon; HOO⁻ adds to boron, the alkyl shifts to oxygen and hydrolysis gives propan-1-ol.

Mechanism step by step

Anti-Markovnikov, syn addition of H and OH across C=C

1. Hydroboration – B adds to the CH₂ end, H to the CH, on one face
2. Hydroperoxide adds – HOO⁻ attacks the empty p orbital of B
3. 1,2-Shift – The alkyl group moves from B to O; HO⁻ leaves
4. Hydroxide adds – Attack on boron
5. Alkoxide leaves – B–O bond breaks
6. Protonation – Propan-1-ol

Key points

• Anti-Markovnikov: OH ends up on the less substituted carbon.
• Syn addition, and the C–B → C–O step keeps the configuration.
• No carbocation, so no rearrangements (unlike acid-catalysed hydration).
• In practice BH₃ adds three times (R₃B); every alkyl group becomes an alcohol.

Drawn with 75 atoms, 16 arrows, 10 shapes – every one editable in MolDraw.

Sources

• Brown & Subba Rao, J. Am. Chem. Soc. 1956, 78, 5694 Original paper
• Kürti & Czakó, Strategic Applications of Named Reactions in Organic Synthesis, Elsevier 2005 Textbook
• Clayden, Greeves & Warren, Organic Chemistry, 2nd ed., OUP 2012 Textbook