An SN2 reaction, or bimolecular nucleophilic substitution, is a type of chemical reaction where a nucleophile attacks an electrophile, resulting in the substitution of one group for another. This process involves a single concerted step, meaning that the bond formation and bond breaking occur simultaneously. The reaction rate depends on the concentration of both the nucleophile and the substrate, which is why it is termed "bimolecular." In an SN2 reaction, the nucleophile approaches the substrate from the opposite side of the leaving group, leading to an inversion of configuration at the carbon center. This reaction typically occurs with primary or secondary alkyl halides, such as bromomethane or chloropropane, and is favored in polar aprotic solvents, which help stabilize the nucleophile.