Which type of carbon structures are likely to undergo the Sn2 mechanism?

The SN2 mechanism, or bimolecular nucleophilic substitution, is favored for substrates that allow for a backside attack by the nucleophile. This is most readily accomplished with primary and secondary carbons because of steric hindrance and the stability of the transition state during the reaction.

In primary carbon structures, the nucleophile can easily approach the carbon atom, as it is not surrounded by bulky groups that would impede this interaction. This ease of access allows for a swift and effective reaction. Secondary carbons also allow for this type of reaction, although with slightly less efficiency due to increased steric hindrance compared to primary carbons.

Tertiary and quaternary carbons, in contrast, experience significant steric hindrance due to the presence of multiple alkyl groups. This hindered access makes the SN2 mechanism infeasible, as the nucleophile cannot effectively approach the carbon to perform the substitution. Instead, these structures typically favor the SN1 mechanism, where the reaction proceeds via the formation of a carbocation.

Thus, the use of primary and secondary carbon structures is essential for the effectiveness of the SN2 mechanism, confirming that the correct answer involves both these types of carbon arrangements.