Nucleophilic addition — NaBH₄ (reduction to alcohols)

Year 2

AQA 3.3.8

Carbonyl & aromatic chemistry · NaBH₄ in water/methanol · room temperature

Reagents: NaBH₄ in water/methanol · Conditions: room temperature

Step 1 of 2

1.The lone pair on :H⁻ attacks the δ+ carbonyl carbon, forming a new C–H bond. The arrow starts on the hydride, not on Na or B.
2.The C=O π bond breaks; both electrons move onto oxygen, giving an alkoxide.

Hydride adds to the carbonyl carbon and the π electrons move to O, giving an alkoxide.

Step 2 of 2

1.A lone pair on the alkoxide O⁻ takes a proton from water, forming the –OH group of the alcohol.

The alkoxide is protonated: propan-2-ol.

Product: propan-2-ol

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