Q: Which of the following statements best describes the rate law for an E2 elimination reaction?

The rate is second order overall: $$\text{rate} = k \times [\text{RX}] \times [\text{Base}].$$

Question 1

Which of the following statements best describes the rate law for an E2 elimination reaction?

Accepted Answer

The rate is second order overall: $$	ext{rate} = k 	imes [	ext{RX}] 	imes [	ext{Base}].$$

Question 2

Why does the E2 reaction exhibit a significant deuterium isotope effect?

Accepted Answer

Because the C–D bond is stronger than the C–H bond, making C–D cleavage slower and indicating that bond breaking occurs in the rate-limiting step.

Question 3

Which geometric arrangement is energetically preferred for the E2 elimination transition state?

Accepted Answer

Anti periplanar geometry, because it allows substituents to be staggered.

Question 4

In the E2 elimination of meso-1,2-dibromo-1,2-diphenylethane, only the E alkene is formed. What does this observation suggest about the mechanism?

Accepted Answer

The reaction requires anti periplanar geometry, which leads selectively to the E alkene.

Question 5

Which of the following best explains why neomenthyl chloride undergoes E2 elimination 200 times faster than menthyl chloride?

Accepted Answer

Neomenthyl chloride has an axial chlorine and an axial hydrogen in the correct trans-diaxial arrangement for E2 elimination.

Question 6

Why does menthyl chloride yield 2-menthene as the major product upon E2 elimination, contrary to Zaitsev’s rule?

Accepted Answer

Because the only available trans-diaxial hydrogen is at a position that leads to 2-menthene.

Question 7

Which of the following is NOT a requirement for an E2 elimination to occur in a cyclohexane ring?

Accepted Answer

The leaving group and the hydrogen must be equatorial.

Question 8

A student replaces all hydrogens at the β-carbon of an alkyl halide with deuterium. How will this affect the rate of the E2 elimination?

Accepted Answer

The rate will decrease because C–D bonds are harder to break than C–H bonds.

Question 9

Which of the following best describes the orbital interactions in the E2 transition state?

Accepted Answer

The sp3 $$\sigma$$ orbitals of the C–H and C–X bonds overlap to form p $$\pi$$ orbitals in the alkene product.

Question 10

Which of the following statements about the stereochemistry of E2 reactions is correct?

Accepted Answer

E2 reactions require the hydrogen and leaving group to be anti periplanar for maximum reactivity.

Question 11

Which of the following best explains why the E2 reaction is considered a concerted process?

Accepted Answer

Bond breaking and bond forming occur simultaneously in a single step.

Question 12

A chemist wants to maximize the rate of E2 elimination in a substituted cyclohexane. Which conformation should they seek?

Accepted Answer

A conformation where both the leaving group and the β-hydrogen are axial and trans to each other.

Question 13

Which of the following is a direct consequence of the anti periplanar requirement in E2 reactions?

Accepted Answer

Only certain stereoisomers of the starting material can yield specific alkene isomers.

Question 14

Which of the following statements about the effect of cyclohexane conformation on E2 elimination is correct?

Accepted Answer

E2 elimination can only occur when the leaving group and the β-hydrogen are both axial.

Question 15

A reaction of 1-bromo-2-phenylethane with a strong base proceeds 7.11 times faster than the same reaction with 1-bromo-2,2-dideuterio-2-phenylethane. What does this observation support?

Accepted Answer

The C–H (or C–D) bond is broken in the rate-limiting step of the E2 reaction.

Question 16

Which of the following best describes the relationship between the E2 and SN2 mechanisms?

Accepted Answer

Both are concerted, single-step reactions involving a transition state with simultaneous bond making and breaking.

The E2 Reaction: Mechanism, Isotope Effect, and Stereochemistry

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