Final answer:
An SN2 reaction causes inversion of configuration at the electrophilic carbon, resulting in the opposite stereochemistry to the starting material, due to a 'backside attack' by the nucleophile.
Step-by-step explanation:
An SN2 reaction, which stands for Substitution Nucleophilic Bimolecular, significantly affects the stereochemistry of the electrophilic carbon. In an SN2 reaction, the incoming nucleophile approaches the electrophilic carbon from the side opposite to the leaving group. As the nucleophile forms a bond with the carbon, the leaving group departs, and the other substituents on the carbon are forced to switch positions to accommodate this change. This causes an inversion of configuration at the electrophilic carbon, resulting in the product having the opposite configuration to the reactant if the reactant carbon is chiral. This phenomenon is often referred to as the 'backside attack' or 'Walden inversion'.