Grignard reagents are organometallic compounds containing a carbon-magnesium bond, typically represented as RMgX, where R is an organic group and X is a halogen. They are highly reactive nucleophiles and are essential in organic synthesis for forming carbon-carbon bonds. Grignard reagents are prepared by reacting an organic halide (alkyl or aryl halide) with magnesium in anhydrous ether or THF (tetrahydrofuran). The reaction is typically carried out under anhydrous conditions to prevent interference from water. The resulting Grignard reagent can react with various electrophiles, facilitating the creation of new carbon-carbon bonds in organic synthesis.