Why does tert-butyl bromide not participate in $S_{N2}$ reactions?

• A. Because the central carbon is highly hindered, making nucleophilic backside attack difficult due to steric effects.
• B. Because tert-butyl bromide is too reactive and decomposes before the reaction can occur.
• C. Because the reaction requires a strong acid, which is not present.
• D. Because the bromide ion is not a good leaving group in this molecule.

Answer: (A)

Verified step by step guidance

1. Identify the structure of tert-butyl bromide: it is a tertiary alkyl halide where the central carbon bonded to the bromine is connected to three other alkyl groups, creating significant steric bulk around the reactive site.
2. Recall the mechanism of an SN2 reaction, which involves a nucleophile performing a backside attack on the electrophilic carbon, leading to a simultaneous displacement of the leaving group in a single step.
3. Understand that for SN2 reactions, steric hindrance around the electrophilic carbon greatly reduces the nucleophile's ability to approach and attack from the backside.
4. Analyze how the bulky tert-butyl group surrounding the central carbon in tert-butyl bromide physically blocks the nucleophile from accessing the backside, thus preventing the SN2 mechanism.
5. Conclude that due to this steric hindrance, tert-butyl bromide does not undergo SN2 reactions efficiently, favoring other mechanisms such as SN1 instead.