SN1 Mechanism Features Carbocation Stability

Steps:

• SN1 involves rate-determining ionization of haloalkane to form a carbocation intermediate.
• The carbocation is planar and sp2 hybridized, allowing resonance or hyperconjugation stabilization.
• Adjacent alkyl groups donate electron density via inductive effect and hyperconjugation, lowering carbocation energy.
• Nucleophile then attacks the stabilized carbocation in a fast step.

Why C is correct:

• Carbocations in SN1 are tertiary > secondary > primary due to stabilization by adjacent alkyl groups through hyperconjugation, as per Markovnikov's rule extensions.

Why the others are wrong:

• A: Nucleophile attacks the carbocation (electrophile), but substitution occurs via addition-elimination, not direct "substitution of an electrophile."
• B: The carbocation intermediate forms from one haloalkane molecule dissociating, not two reacting molecules.
• D: The intermediate is a positively charged carbocation, not uncharged.

Final answer: C