The SN2 mechanism is a type of nucleophilic substitution reaction where a nucleophile attacks an electrophile, resulting in the simultaneous displacement of a leaving group. This process occurs in a single concerted step, meaning that both bond formation and bond breaking happen at the same time. The reaction rate depends on the concentration of both the nucleophile and the substrate, making it a second-order reaction. In the SN2 mechanism, the nucleophile approaches the substrate from the opposite side of the leaving group, leading to an inversion of configuration at the carbon center. This stereochemical outcome is significant in organic chemistry, especially when dealing with chiral molecules.