SL - Elimination

Question 1

What does the product ratio depend on?

Answer 1

Relative rates of substitution vs elimination

Question 2

What mechanism occurs when the proton is removed whilst the leaving group departs?

Answer 2

E2 mechanism

Question 3

What mechanism occurs when:
1. The proton is removed
2. The leaving group departs

Answer 3

E1cb mechanism

Question 4

What mechanism occurs when:
1. The leaving group departs
2. The proton is removed

Answer 4

E1 mechanism

Question 5

Describe the E2 mechanism

Answer 5

• One-step mechanism
• Rate depends on [Brønsted base] and [alkyl halide]
• RDS is bimolecular

Question 6

Is the E2 mechanism stereoselective?

Answer 6

Yes - only gives one specific alkene isomer as the proton is removed on the opposite side to the leaving group

Question 7

Describe the E1 mechanism

Answer 7

Two-step mechanism
1. Leaving group departs (SLOW)
2. Proton is removed (FAST)

Rate is dependent on [alkyl halide]
RDS is unimolecular

Question 8

Describe the E1cb mechanism

Answer 8

Two-step mechanism
1. Proton is removed
2. Leaving group departs

Rate is dependent on [carbanion] (step 2)
RDS is unimolecular

Question 9

How can the intermediate carbanion be stabilised?

Answer 9

Delocalisation - forms resonance structures