Q36E - Organic Chemistry (Mcmurry)

Question

Phenols generally have lower pKa’s than aliphatic alcohols because of resonance stabilization with the aromatic ring. Draw all of the resonance contributors for the phenolate ions below. Make note of how the substituents either stabilize or destabilize the system.

Step-by-Step Solution

Answer

Step 1: Resonating structure

The delocalization of the 𝛑 electrons produces the structures, and the structures are called the Lewis acid.

Step 2: Resonating structure of Phenoxide a

Phenoxides are formed by the phenol by abstraction of the hydroxyl protons. They are more acidic in nature, and have a low pKa value, and show resonance as oxygen having a negative charge, as shown below. Here, the last resonating structure destabilizes the molecule due to the negative charge at para with the alkyl group.

Step 3: Resonating structure of Phenoxide b

Phenoxides are formed by the phenol by the abstraction of the hydroxyl proton. They are more acidic in nature, have a low pKa value, and show resonance as oxygen having a negative charge, as shown below:

Step 4: Resonating structure of Phenoxide C

Phenoxides are formed by the phenol by the abstraction of the hydroxyl proton. They are more acidic in nature, have a low pKa value, and show resonance as oxygen having a negative charge. as shown below. Here, the third structure is stabilized because the oxygen atom present has lone pair, which also takea part in delocalization and makes the system more stable: