Lisäyseliminaatiomekanismi

Lisäyseliminaatiomekanismi, often translated as addition-elimination mechanism, is a reaction pathway observed in organic chemistry. It typically describes the reaction of nucleophiles with electrophilic species that possess a leaving group. The mechanism involves two distinct steps. First, the nucleophile attacks the electrophilic center, forming a temporary intermediate. This intermediate is often referred to as a Meisenheimer complex or an anionic sigma complex, where the carbon atom being attacked becomes pentavalent. In the second step, the leaving group departs from this intermediate, regenerating the aromaticity or restoring the original bonding arrangement and forming the final product. This mechanism is characteristic of certain nucleophilic aromatic substitution reactions, particularly those where the aromatic ring is activated by electron-withdrawing groups. It is also encountered in nucleophilic acyl substitution reactions, such as the hydrolysis of esters or the reaction of acid halides with nucleophiles. The rate of the reaction is often dependent on the strength of the nucleophile and the electrophilicity of the substrate. The stability of the intermediate plays a crucial role in determining the feasibility of the addition-elimination pathway.