Final answer:
Alkyl halides that usually undergo SN2 reactions are methyl and primary alkyl halides due to reduced steric hindrance, favored by polar aprotic solvents, with a nucleophile attacking the electrophilic carbon opposite the leaving group, resulting in stereochemical inversion.
Step-by-step explanation:
In theory, the alkyl halides that undergo SN2 reactions are those that are less sterically hindered, such as methyl and primary alkyl halides. The ability for an alkyl halide to participate in an SN2 reaction is determined by several factors, including the structure of the substrate, the nucleophile, the solvent, and the leaving group. For example, ethyl bromide is a primary alkyl halide that can be converted to other organic compounds via an SN2 reaction, where a nucleophile attacks the electrophilic carbon opposite to the leaving group, typically with inversion of stereochemistry.
Polar aprotic solvents are suitable for SN2 reactions as they allow the nucleophiles to be free to approach the electrophilic carbon of the substrate without being solvated by hydrogen bonding. In contrast, secondary and especially tertiary alkyl halides are more likely to undergo E2 reactions due to steric hindrance preventing the nucleophile’s approach, thus favoring elimination over substitution.
The SN2 reaction mechanism is characterized by the simultaneous making and breaking of bonds in a single concerted step, where the incoming nucleophile and the leaving group are involved in the transition state, leading to a trigonal planar arrangement perpendicular to the bond being broken and formed. This process typically occurs in primary or methyl substrates but not in tertiary substrates due to steric hindrance.