Propose a mechanism for each reaction.
(a)
(b)

Verified step by step guidance

1. Step 1 (Reaction A): Protonation of one of the hydroxyl groups occurs in the presence of H⁺, making it a better leaving group. This forms a carbocation intermediate.
2. Step 2 (Reaction A): The carbocation undergoes rearrangement to stabilize itself, potentially forming a more stable tertiary carbocation.
3. Step 3 (Reaction A): The remaining hydroxyl group acts as a nucleophile and attacks the carbocation, leading to the formation of a cyclic intermediate.
4. Step 4 (Reaction A): Deprotonation of the cyclic intermediate occurs, resulting in the formation of the ketone product.
5. Step 5 (Reaction B): In the presence of H₂SO₄, the hydroxyl group is protonated, making it a better leaving group. This leads to the formation of a carbocation intermediate, which undergoes rearrangement and nucleophilic attack by the phenyl groups to form the ketone product.

Key Concepts

Protonation

Protonation is the addition of a proton (H+) to a molecule, which can enhance its reactivity. In the context of organic reactions, protonation often occurs at sites of high electron density, such as alcohols or double bonds, making them more susceptible to nucleophilic attack or facilitating bond rearrangements.

Nucleophilic Attack

Nucleophilic attack refers to the process where a nucleophile, an electron-rich species, attacks an electrophile, an electron-deficient species. This is a fundamental step in many organic reactions, leading to the formation of new bonds. Understanding the nature of nucleophiles and electrophiles is crucial for predicting reaction outcomes.

Rearrangement Reactions

Rearrangement reactions involve the reorganization of atoms within a molecule, often resulting in structural isomers. These reactions can be driven by the stability of intermediates formed during the process, such as carbocations. Recognizing the conditions that favor rearrangements is essential for proposing accurate reaction mechanisms.