Bondline / Reactions

Reduction with NaBH₄

Borohydride delivers hydride (H⁻) to the carbonyl carbon; protonation of the alkoxide gives the alcohol. Ketones give secondary alcohols, aldehydes primary.

Carbonyl addition · 2 steps

Conditions

NaBH₄ in methanol or ethanol. Mild: does not reduce esters or acids.

Mechanism in 2 steps

Red curly arrows show where each pair of electrons moves.

HBH3−OO−HO++
Step 1A B–H bond delivers hydride to carbon; the C=O π electrons move onto oxygen.
O−HOOHO−MeOH++
Step 2The alkoxide is protonated by the solvent.

About carbonyl addition reactions

The carbon of a C=O is δ+, so nucleophiles attack it and the π electrons move onto oxygen. Weak nucleophiles often need acid to activate the carbonyl first.

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