Swap magnesium for lithium and the C–metal bond gets more ionic, so R–Li is a fiercer carbanion than a Grignard.
The big picture — one nucleophile, four electrophiles:
One idea: R–Li delivers its carbon to whatever electrophile is in the flask.
1. Organolithiums form from an alkyl halide and two equivalents of lithium.
An alkyl or aryl halide reacts with two equivalents of Li in dry, inert solvent: R–X + 2 Li → R–Li + LiX.
2. The C–Li bond is more ionic than C–Mg, so R–Li is a stronger nucleophile and base.
The nucleophilic carbon attacks an electrophilic carbonyl carbon, giving an alkoxide that is protonated on workup.
3. R–Li adds to aldehydes and ketones to give 1°, 2°, or 3° alcohols.
Formaldehyde → 1°, other aldehydes → 2°, ketones → 3° — and R–Li still forces the bond on hindered ketones where a Grignard stalls.
Acetone + methyllithium → tert-butanol, a tertiary alcohol.
4. R–Li adds to carbon dioxide to give a carboxylic acid.
The carbanion adds to CO2 to give a lithium carboxylate, and workup yields a carboxylic acid one carbon longer than R.
Methyllithium + CO2 → acetic acid after workup.
5. R–Li adds twice to an ester, giving a 3° alcohol.
The first equivalent expels the alkoxide to make a ketone in situ; a second adds at once, so two equivalents give a 3° alcohol with two identical R groups.
Methyl acetate + 2 CH3Li → tert-butanol (two new methyls).
6. R–Li turns a carboxylic acid into a ketone — Grignards cannot.
The first equivalent deprotonates the acid; a second adds to the carboxylate to form a stable gem-diolate dianion that collapses to a ketone only on workup.
Acetic acid + 2 CH3Li → acetone. A transformation no Grignard can match.
7. As strong bases, R–Li deprotonate terminal alkynes and any protic H.
They deprotonate terminal alkynes (pKa ≈ 25) and α-carbons to enolates, but any protic H (water, O–H, N–H) quenches R–Li to R–H.
8. Summary
R–X + 2 Li → R–Li · aldehydes/ketones → 1°/2°/3° alcohols · CO2 → acid · ester + 2 eq → 3° alcohol · acid + 2 eq → ketone (Grignards can't) · strong base for alkynes/enolates · any protic H kills it. See Grignard reagents.
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Because the C–Li bond is even more ionic than the C–Mg bond. Lithium is more electropositive, so the electrons sit more fully on carbon, giving it greater carbanion character — which raises both its nucleophilicity and its basicity.
It gives acetone (a ketone). The first equivalent deprotonates the acid; the second adds to the carboxylate to form a stable gem-diolate dianion that collapses to the ketone only on workup. A Grignard is simply consumed as R–H by the acidic O–H and stops there.
The first addition expels the alkoxide leaving group to make a ketone in situ, which is more reactive than the ester. A second equivalent adds before you can stop it, so workup yields a tertiary alcohol carrying two identical R groups (e.g. methyl acetate + 2 CH3Li → tert-butanol).
Any protic hydrogen — water and other O–H sources, N–H bonds, or a terminal alkyne C–H — protonates R–Li to R–H. Air is also a hazard, since many organolithiums are pyrophoric. That is why they are used in dry solvents under inert gas, with acidic workup only at the end.
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