A tertiary alkyl halide usually undergoes nucleophilic substitution by the SN1 mechanism because
Correct answer: A. the tertiary carbocation formed is relatively stable and the carbon is too hindered for back side attack
- A. the tertiary carbocation formed is relatively stable and the carbon is too hindered for back side attack
- B. tertiary halides have the weakest carbon to halogen bond
- C. tertiary carbon atoms carry a full positive charge already
- D. the nucleophile is always weak
Explanation
Three electron releasing alkyl groups spread the positive charge and stabilise the carbocation, so the slow ionisation step becomes feasible, and at the same time those bulky groups block the approach a concerted SN2 attack would need. The rate therefore depends only on the halide concentration, giving first order kinetics. Because the planar carbocation can be attacked from either face, a racemic mixture results.
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About Nucleophilic Substitution
Nucleophilic substitution replaces a leaving group in an alkyl halide when an electron-rich nucleophile attacks the carbon atom. The topic compares SN1 and SN2 mechanisms, including reaction conditions, substrate structure, solvent effects, nucleophile strength, carbocation formation and stereochemical changes, and distinguishes substitution from elimination.
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