SN2reaktsioonides

SN2reaktsioonid, also known as bimolecular nucleophilic substitution reactions, are a fundamental type of organic chemical reaction. They involve the substitution of a leaving group on an sp3 hybridized carbon atom by a nucleophile. The "SN2" designation indicates that the reaction is a bimolecular substitution, meaning that the rate of the reaction depends on the concentration of both the substrate and the nucleophile. This is in contrast to SN1 reactions, which are unimolecular.

A key characteristic of SN2 reactions is their stereochemical outcome. The nucleophile attacks the carbon atom from the backside, directly opposite the leaving group. This "inversion of configuration" means that if the carbon atom is chiral, its stereochemistry will be inverted during the reaction. For example, if the starting material has an R configuration at the reaction center, the product will have an S configuration, and vice versa, assuming the incoming nucleophile and leaving group have the same priority ranking.

SN2 reactions are favored by several factors. Steric hindrance around the reaction center is a significant impediment; less hindered substrates react faster. Primary alkyl halides are generally more reactive than secondary ones, and tertiary alkyl halides typically do not undergo SN2 reactions due to excessive steric crowding. Strong, small nucleophiles also promote SN2 reactions. Polar aprotic solvents, such as dimethyl sulfoxide (DMSO) or acetonitrile, are often used as they solvate the cation associated with the nucleophile but leave the nucleophile itself relatively free to react.