Grignard reaction
Organometallic reaction forming carbon–carbon bonds via Grignard reagents.
The Grignard reaction is an organometallic chemical reaction in which carbon alkyl, allyl, vinyl, or aryl magnesium halides (Grignard reagent) are added to the carbonyl groups of either an aldehyde or ketone under anhydrous conditions. This reaction is important for the formation of carbon–carbon bonds.
- discovered_by
- François Auguste Victor Grignard
- field
- Organometallic chemistry
- nationality
- French
- known_for
- Grignard reaction and Grignard reagents
- nobel_prize
- 1912 Nobel Prize in Chemistry
Lore & Background
He was awarded the 1912 Nobel Prize in Chemistry for this work. The reaction of an organic halide with magnesium is not a Grignard reaction, but provides a Grignard reagent. Classically, the Grignard reaction refers to the reaction between a ketone or aldehyde group with a Grignard reagent to form a primary or tertiary alcohol. However, some chemists understand the definition to mean all reactions of any electrophiles with Grignard reagents, leading to dispute about the modern definition. The Merck Index, published online by the Royal Society of Chemistry, acknowledges the classical definition and notes that a more modern interpretation extends the scope to include addition to a wide variety of electrophilic substrates.
Reader's Guide
The Grignard reaction is significant for its role in forming carbon–carbon bonds, a fundamental process in organic synthesis. Because carbon is more electronegative than magnesium, the carbon attached to magnesium acts as a nucleophile and attacks the electrophilic carbon atom in the polar bond of a carbonyl group. The addition typically proceeds through a six-membered ring transition state. When the Grignard reagent adds to an aldehyde or a prochiral ketone, the Felkin-Anh model or Cram's Rule can usually predict which stereoisomer will be formed. An alternative single electron transfer (SET) mechanism involving a ketyl radical intermediate has also been proposed, with a recent computational study suggesting the operative mechanism is substrate-dependent. The reaction must be conducted under anhydrous conditions; otherwise, the Grignard reagent acts as a base rather than a nucleophile. Variants such as Turbo-Grignards (modified with lithium chloride) improve chemoselectivity, and heterometal-modified Grignard reagents (e.g., with copper, cerium, nickel, or palladium) allow selective additions or cross-coupling reactions.
Did You Know?
- Grignard was awarded the 1912 Nobel Prize in Chemistry for discovering the reaction and reagents.
- The reaction must be conducted under anhydrous conditions; otherwise, the Grignard reagent acts as a base instead of a nucleophile.
- Turbo-Grignards are Grignard reagents modified with lithium chloride and are more chemoselective than conventional Grignard reagents.
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