rMgX

RMgX denotes a Grignard reagent, an organomagnesium compound of general formula RMgX, where R is an alkyl or aryl group and X is a halogen (Cl, Br, or I). They are prepared by reacting an organohalide with magnesium metal in an anhydrous ether solvent, such as diethyl ether or THF, under strictly moisture- and air-free conditions. The resulting species are highly reactive nucleophiles and bases; they are typically used in solution and must be prepared fresh and used promptly due to sensitivity to air and moisture.

Solvent and structure: The ether coordinates to magnesium, stabilizing the carbanion-like center. THF often affords more soluble and reactive reagents than diethyl ether. Grignard reagents require rigorously dry conditions and are usually handled under inert atmosphere.

Reactivity: RMgX reagents act as carbon nucleophiles. They add to carbonyl compounds to form alcohols after workup: with formaldehyde, primary alcohols; with other aldehydes, secondary alcohols; with ketones, tertiary alcohols. They also react with carbon dioxide to give carboxylic acids upon acidic workup; with epoxides, they open the ring to yield alcohols with extended carbon skeleton; with esters, they form tertiary alcohols after two equivalents of RMgX and hydrolysis.

Applications and limitations: Grignard reagents are versatile for constructing alcohols and for introducing alkyl or aryl groups adjacent to carbonyl fragments. They are highly reactive and incompatible with water, oxygen, acids, and many functional groups. Handling requires dry solvents, inert atmosphere, and careful safety practices.