Tertiary halogenoalkane favors SN1 mechanism

Steps:

• Identify the structure: 3-bromo-3-ethylpentane has a tertiary carbon attached to Br, bonded to three alkyl groups (two ethyls and one from pentane chain).
• Recall SN1/SN2 dependence: Tertiary halides prefer SN1 due to carbocation stability; primary/secondary may favor SN2.
• Determine intermediate: SN1 forms a carbocation intermediate stabilized by hyperconjugation and inductive effects from alkyl groups.
• Match to options: SN1 with cation stabilization by three alkyl groups fits.

Why B is correct:

• SN1 mechanism involves a planar carbocation intermediate, stabilized by three alkyl groups via hyperconjugation, as per carbocation stability rules.

Why the others are wrong:

• A: SN1 uses a cation, not anion intermediate.
• C: SN2 is concerted with no stable intermediate; unsuitable for tertiary due to steric hindrance.
• D: SN2 has no cation intermediate; tertiary structure blocks backside attack.

Final answer: B