Organic Chemistry : Help with E1 Reactions

Study concepts, example questions & explanations for Organic Chemistry

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Example Questions

Example Question #1 : Help With E1 Reactions

E1

The above image undergoes an E1 elimination reaction in a lab. The researchers note that the major product formed was the "Zaitsev" product. Which of the following compounds did the observers see most abundantly when the reaction was complete?

Possible Answers:

E4

E2

E7

E3

None of these

Correct answer:

E4

Explanation:

The Zaitsev product is the most stable alkene that can be formed. This is the major product formed in E1 elimination reactions, because the carbocation can undergo hydride shifts to stabilize the positive charge. The most stable alkene is the most substituted alkene, and thus the correct answer.

E4

Example Question #2 : Help With E1 Reactions

Which series of carbocations is arranged from most stable to least stable? 

Possible Answers:

Primary, secondary, tertiary, methyl

Methyl, primary, secondary, tertiary

Tertiary, secondary, primary, methyl

The stability of a carbocation depends only on the solvent of the solution

Methyl, tertiary, secondary, primary

Correct answer:

Tertiary, secondary, primary, methyl

Explanation:

Tertiary carbocations are stabilized by the induction of nearby alkyl groups. Since the carbocation is electron deficient, it is stabilized by multiple alkyl groups (which are electron-donating). Less substituted carbocations lack stability.

Example Question #3 : Help With E1 Reactions

Which of the following is true for E2 reactions?

Possible Answers:

The proton and the leaving group should be anti-periplanar

The reaction is bimolecular

A double bond is formed

All of these

Correct answer:

All of these

Explanation:

All are true for E2 reactions. E2 reactions are bimolecular, with the rate dependent upon the substrate and base. Both E1 and E2 reactions generally follow Zaitsev's rule and form the substituted double bond. The stereochemistry for E2 should be antiperiplanar (this is not necessary for E1).

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