Multiple Choice
Which of the following reaction sequences best represents an elimination of an alkyl halide with a carbocation rearrangement?
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8. Elimination Reactions
E1 Reaction
Multiple Choice
Which of the following molecules is most likely to undergo an reaction when stirred in water?
A
(allyl bromide)
B
(tert-butyl bromide)
C
(ethyl chloride)
D
(ethyl bromide)
Verified step by step guidance1
Step 1: Understand the mechanism of an E1 reaction. E1 (unimolecular elimination) involves two main steps: first, the leaving group departs to form a carbocation intermediate; second, a base removes a proton from a β-carbon, resulting in the formation of a double bond.
Step 2: Identify the stability of the carbocation intermediate formed after the leaving group leaves. More stable carbocations favor the E1 mechanism because the rate-determining step is carbocation formation. Carbocation stability order is tertiary > secondary > primary > methyl.
Step 3: Analyze each molecule's structure to determine the type of carbocation that would form upon loss of the leaving group (Br or Cl). For example, tert-butyl bromide forms a tertiary carbocation, allyl bromide forms an allylic carbocation (which is resonance stabilized), ethyl chloride and ethyl bromide form primary carbocations (less stable).
Step 4: Consider the solvent and conditions. Water is a polar protic solvent that stabilizes carbocations and can promote E1 reactions, especially with stable carbocations.
Step 5: Conclude which molecule is most likely to undergo E1 based on carbocation stability and reaction conditions. The molecule that forms the most stable carbocation intermediate (typically tertiary or resonance-stabilized) will favor the E1 mechanism.
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