Pick correct pair about the difference between E1 and E2 mechanism of tertiary butyl bromide forming an alkene.

Correct answer: B. E1 mechanism- weak base and alkyl halide, E2 mechanism- strong base and alkyl halide

  • A. E1 mechanism- strong base and alkyl halide, E2 mechanism- weak base and alkyl halide
  • B. E1 mechanism- weak base and alkyl halide, E2 mechanism- strong base and alkyl halide
  • C. E1 mechanism- strong base and alkyl halide, E2 mechanism- strong base and alkyl halide
  • D. E1 mechanism- weak base and alkyl halide, E2 mechanism- weak base and alkyl halide

Explanation

E1 mechanism- weak base and alkyl halide, E2 mechanism- strong base and alkyl halide.In the E1 mechanism, the rate-determining step is the formation of a carbocation intermediate, followed by the loss of a leaving group and the formation of a double bond. The reaction proceeds in two steps and requires a strong base to remove a proton from the beta-carbon.In contrast, in the E2 mechanism, the reaction occurs in a single step and requires a strong base to remove a proton from the beta-carbon and eliminate the leaving group at the same time.so, in this case both E1 and E2 mechanisms can occur. However, the E1 mechanism is favored with a weak base, whereas the E2 mechanism is favored with a strong base. Therefore, the correct pair is B) El mechanism- weak base and alkyl halide, E2 mechanism- strong base and alkyl halide.

This question appeared on the NUMS 2019 (cancelled sitting) paper, which you can sit online with every answer explained.

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About Elimination Reactions

Elimination reactions remove a leaving group and a hydrogen atom from adjacent carbon atoms to form an alkene. The topic covers dehydrohalogenation of alkyl halides, E1 and E2 mechanisms, the role of base, solvent and substrate structure, and Zaitsev orientation, which is often contrasted with substitution.

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