Grignard reaction with phenylmagnesium bromide: practice and mechanism
The phenyl group of the Grignard reagent attacks the carbonyl carbon. After acidic workup an alcohol with a new C–phenyl bond forms (secondary from aldehydes, tertiary from ketones).
Example
The phenyl group of the Grignard reagent attacks the carbonyl carbon as a carbanion. Aldehydes give secondary, ketones tertiary alcohols with a phenyl ring; esters react twice (two phenyl groups).
Mechanism step by step
- 1
In phenylmagnesium bromide the C–Mg bond pair is strongly polarised toward carbon: the phenyl carbon is nucleophilic (carbanion-like).
- 2
The phenyl carbon attacks the carbonyl carbon and the C=O bond folds to the alkoxide (Mg²⁺ as counter-ion).
- 3
Acidic workup protonates the alkoxide to the alcohol.
Practice tasks
Which product forms, which reagent is needed? After each answer you see the explanation.
Which main product forms?
Typical mistakes
Often confused with: Grignard reaction
Frequently asked questions
Which alcohol forms from which starting material?
Formaldehyde → primary, other aldehydes → secondary, ketones → tertiary. Esters react twice and give tertiary alcohols with two phenyl groups.
Why must everything be dry?
Grignard reagents are very strong bases. Water, alcohols or acids protonate them at once to benzene and the reagent is lost.