Which type of alkyl halides gives SN2 mechanism?

Explanation

The SN2 (Substitution Nucleophilic Bimolecular) mechanism typically occurs with primary (1°) alkyl halides. The SN2 mechanism involves a nucleophilic attack by a nucleophile on the electrophilic carbon of the alkyl halide, resulting in the substitution of the halogen atom with the nucleophile. In the SN2 reaction, the nucleophile approaches the carbon atom from the opposite side of the leaving group, leading to inversion of stereochemistry.The SN2 mechanism is favored for primary alkyl halides because the carbon atom attached to the halogen is less sterically hindered compared to secondary or tertiary carbon atoms. The steric hindrance created by bulky groups attached to the carbon atom can hinder the approach of the nucleophile and decrease the likelihood of an SN2 reaction.For example, an SN2 reaction can occur with a primary alkyl halide such as methyl chloride (CH3Cl):CH3Cl + Nu^- -> CH3Nu + Cl^-In this reaction, Nu^- represents the nucleophile, which can be an anionic species such as hydroxide ion (OH^-) or cyanide ion (CN^-).It's important to note that there are other mechanisms, such as SN1 (Substitution Nucleophilic Unimolecular) and E1 (Elimination Unimolecular), which occur with different types of alkyl halides depending on their structure and reaction conditions.SN2 reactions, or Bimolecular Nucleophilic Substitution reactions involve two molecules, the nucleophile and the alkyl halide in the slow step of the process. The mechanism involves an attack from the nucleophile and simultaneous removal of the leaving group from the alkyl halide molecule. This happens for primary alkyl halides only because they have the least steric hindrance (as compared to tertiary or secondary alkyl halides) to allow the attack from nucleophiles. Therefore, option D is correct.