Bimolecular nucleophilic substitution reactions, commonly referred to as S_N2 reactions, are an important concept in organic chemistry. Let's analyze the options provided in the question to determine which statements are correct.
- Carbocation Formation:
The S_N2 reaction proceeds via a single concerted step mechanism without the formation of a carbocation. Instead, the nucleophile attacks the substrate directly, displacing the leaving group in a one-step process. Thus, this option is incorrect. - Inversion of Configuration:
In S_N2 reactions, if the reacting center is chiral, the reaction leads to an inversion of configuration at the carbon center. This inversion is often described as a "backside attack" of the nucleophile. Hence, this option is correct. - Effect of Polar Solvents:
The S_N2 reaction is enhanced when carried out in polar aprotic solvents. These solvents do not solvate anions strongly and therefore allow the nucleophile to be more reactive. Thus, this statement is correct. - Reaction Intermediate:
The description of a trigonal bipyramidal intermediate is incorrect for an S_N2 reaction. This incorrect notion may arise from confusing it with S_N1 reactions or other mechanisms. Thus, this option is incorrect for S_N2 .
Therefore, the correct responses are the second and third options: "There is an inversion of configuration if the reacting center is chiral," and "Reaction is enhanced when carried out in polar solvents."