Bondline / Reactions

Grignard addition

The C–Mg bond is polarised so carbon is nucleophilic; it adds to the carbonyl carbon making a new C–C bond. Acidic workup gives the alcohol. Ketones give tertiary alcohols.

Carbonyl addition · 2 steps

Conditions

RMgBr in dry ether or THF (water destroys the reagent), then H₃O⁺ workup.

Mechanism in 2 steps

Red curly arrows show where each pair of electrons moves.

MgBrOO−HOH2+++
Step 1The C–Mg electrons attack the carbonyl carbon, forming a C–C bond; the π electrons move to oxygen.
O−HOH2+OHH2OH₃O⁺++
Step 2Acidic workup protonates the alkoxide.

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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