Organometallic Nucleophiles: Grignard and Organolithium Reagents
Bonding carbon to a metal reverses the usual polarity and turns that carbon into a strong nucleophile. It is the most direct way to join two carbon fragments, and its weakness is that it reacts with almost anything acidic.
What a learner can do afterwards
- Explains the polarity reversal from the electronegativity difference and marks the nucleophilic carbon
- Predicts the alcohol formed from a stated reagent and carbonyl compound, including the double addition with esters
- Explains why the reaction fails in the presence of water, alcohols or acidic protons
- Chooses a protecting strategy that allows a Grignard reaction on a molecule with an acidic group
1 · Read
Bonding carbon to a metal reverses the usual polarity. Magnesium is far less electronegative than carbon, so the bond puts partial negative charge on carbon. That carbon is nucleophilic, the reverse of an alkyl halide carbon. Mark it in every mechanism you draw.
Formaldehyde gives a primary alcohol, other aldehydes give secondary alcohols, and ketones give tertiary alcohols. Esters add twice to give tertiary alcohols with two identical groups from the reagent. Count the reagent copies: esters take two.
The reagent dies on contact with anything acidic. Water, alcohols, and acids protonate it instantly, giving the plain alkane and killing the nucleophile. Dry ether solvent, no protic sources, and often an inert atmosphere keep it alive.
Mask any acidic group first, for example as an ether or silyl ether, then run the Grignard step and deprotect. The mask must survive base and release under conditions the product tolerates. Plan the protection before you pick the partners.
Metal makes carbon nucleophilic, the carbonyl decides the alcohol class, and every acidic proton must be masked or excluded.
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8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.