One of the following dichloronorbornanes undergoes elimination much faster than the other. Determine which one reacts faster, and explain the large difference in rates.

Verified step by step guidance

1. Step 1: Analyze the structures of the cis- and trans-dichloronorbornanes. The cis isomer has both chlorine atoms on the same side of the bicyclic ring system, while the trans isomer has the chlorine atoms on opposite sides of the ring system.
2. Step 2: Consider the elimination reaction mechanism. The reaction involves the removal of a hydrogen atom and a chlorine atom to form a double bond. This is typically an E2 elimination mechanism, which requires the hydrogen and chlorine atoms to be anti-periplanar (i.e., opposite sides of the same plane).
3. Step 3: Evaluate the geometry of the cis isomer. In the cis isomer, the hydrogen atom and chlorine atom that are candidates for elimination are not anti-periplanar due to the rigid bicyclic structure. This makes elimination less favorable.
4. Step 4: Evaluate the geometry of the trans isomer. In the trans isomer, the hydrogen atom and chlorine atom are anti-periplanar, which aligns perfectly for the E2 elimination mechanism. This makes elimination much faster for the trans isomer.
5. Step 5: Conclude that the trans isomer undergoes elimination much faster than the cis isomer due to the anti-periplanar geometry required for the E2 mechanism, which is achievable in the trans isomer but not in the cis isomer.

Key Concepts

Elimination Reactions

Elimination reactions involve the removal of a small molecule from a larger one, typically resulting in the formation of a double bond. In organic chemistry, these reactions can follow either an E1 or E2 mechanism, which differ in their steps and conditions. Understanding the mechanism is crucial for predicting the rate and outcome of the reaction.

Steric Hindrance

Steric hindrance refers to the repulsion between bulky groups in a molecule that can impede reactions. In the context of elimination reactions, steric hindrance can affect the accessibility of the leaving group and the formation of the double bond. The spatial arrangement of substituents, such as in cis and trans isomers, plays a significant role in determining the reaction rate.

Cis-Trans Isomerism

Cis-trans isomerism is a form of stereoisomerism where the relative positioning of substituents differs around a double bond or a ring structure. In the case of dichloronorbornanes, the cis isomer may allow for a more favorable transition state during elimination due to less steric hindrance compared to the trans isomer, leading to a faster reaction rate.