E_2, or E2, is a type of elimination reaction in organic chemistry where two substituents are removed from a molecule, resulting in the formation of a double bond. This process typically involves a base that abstracts a proton while a leaving group departs simultaneously. E_2 reactions are characterized by their concerted mechanism, meaning that bond breaking and bond formation occur in a single step. E_2 reactions are commonly observed in alkanes and alkyl halides, where the presence of a strong base is crucial for the reaction to proceed. The stereochemistry of the starting material can influence the outcome, often leading to specific geometric isomers. Understanding E_2 is essential for synthesizing alkenes and studying reaction mechanisms in organic chemistry.