Which halides are considered acceptable for SN2 reactions?

In SN2 reactions, the reactivity of halides is influenced by the degree of substitution at the carbon atom to which the halide is attached. The mechanism of SN2 is characterized by a nucleophile attacking the carbon and displacing the leaving group (the halide) in a single concerted step.

1° and 2° halides are considered acceptable substrates for SN2 reactions because they provide less steric hindrance. In a 1° halide, the carbon atom is attached to only one other carbon, allowing for easier access for the nucleophile. In a 2° halide, there are two carbons attached. While this introduces more steric hindrance compared to the 1° halide, the reaction can still occur, though it may proceed more slowly than with a 1° halide.

Conversely, 3° halides are not suitable for SN2 reactions because the steric hindrance is significantly greater due to the three carbon groups surrounding the carbon with the halide. This bulky environment prevents the nucleophile from effectively attacking the target carbon, thereby restricting the SN2 mechanism.

Methyl halides, being a subset of 1° halides, are also ideal candidates for SN2