Write a mechanism that explains the formation of the following product. In your mechanism, explain the cause of the rearrangement, and explain the failure to form the Zaitsev product.

Verified step by step guidance

1. Step 1: Protonation of the alcohol group - The reaction begins with the protonation of the hydroxyl group (-OH) on the CH2OH substituent by sulfuric acid (H2SO4). This forms a good leaving group, water (H2O), and converts the alcohol into a positively charged intermediate.
2. Step 2: Formation of a carbocation - The water molecule leaves, resulting in the formation of a carbocation at the CH2 position. This carbocation is initially a primary carbocation, which is unstable.
3. Step 3: Carbocation rearrangement - To stabilize the carbocation, a hydride shift occurs. A hydrogen atom from the adjacent bridgehead carbon migrates to the carbocation center, resulting in a more stable tertiary carbocation. This rearrangement is driven by the increased stability of tertiary carbocations compared to primary carbocations.
4. Step 4: Elimination reaction - Under the influence of heat, a β-hydrogen is removed from the tertiary carbocation, leading to the formation of a double bond. The elimination follows the E1 mechanism, where the leaving group departs first, followed by the elimination of the β-hydrogen.
5. Step 5: Explanation of product formation - The product formed is not the Zaitsev product because the steric constraints of the bicyclic structure favor the formation of the less substituted alkene. The bulky nature of the bicyclic system prevents the formation of the more substituted double bond, which would typically be favored in Zaitsev's rule.

Key Concepts

Elimination Reactions

Elimination reactions involve the removal of atoms or groups from a molecule, resulting in the formation of a double bond. In organic chemistry, these reactions can follow either an E1 or E2 mechanism, depending on the conditions and the structure of the substrate. Understanding the type of elimination is crucial for predicting the products formed, including the possibility of rearrangements.

Zaitsev's Rule

Zaitsev's Rule states that in elimination reactions, the more substituted alkene (the more stable product) is typically favored. This is due to the stability of the alkene formed, as more substituted alkenes have lower energy and are more thermodynamically stable. However, certain conditions, such as steric hindrance or the presence of strong bases, can lead to the formation of less substituted products instead.

Carbocation Rearrangement

Carbocation rearrangement occurs when a carbocation intermediate shifts to a more stable configuration during a reaction. This can involve hydride shifts or alkyl shifts, leading to the formation of a more stable carbocation. Understanding this concept is essential for predicting the outcome of reactions, especially when explaining why a particular product is formed instead of the expected Zaitsev product.