What are alcohols and phenols?

Both 2 and 3

The correct answer is option 4 - Both 2 and 3

Let us dive into the reasoning behind why alcohols and phenols are classified as Bronsted acids.

Alcohols and Phenols:

Alcohols: Organic compounds with a hydroxyl group \((-OH)\) attached to an aliphatic carbon atom. Example: Ethanol \((CH_3CH_2OH)\)

Phenols: Organic compounds with a hydroxyl group \((-OH) attached to an aromatic ring. Example: Phenol

Bronsted Acid Definition

A Bronsted acid is a substance that can donate a proton \((H^+)\).

Acidic Behavior of Alcohols and Phenols

Proton Donation:

Alcohols: In an aqueous solution, alcohols can lose a proton from the hydroxyl group, producing an alkoxide ion \((R-O^-)\) and a proton \((H^+)\).  Example: Ethanol can donate a proton as follows:

\(\text{CH}_3\text{CH}_2\text{OH} \rightarrow \text{CH}_3\text{CH}_2\text{O}^- + \text{H}^+\)

Phenols:

Phenols can also lose a proton from the hydroxyl group, producing a phenoxide ion \((C_6H_5O^-)\) and a proton \((H^+)\). Phenols are generally stronger acids than alcohols because the phenoxide ion is stabilized by resonance.

Example: Phenol can donate a proton as follows:

\(\text{C}_6\text{H}_5\text{OH} \rightarrow \text{C}_6\text{H}_5\text{O}^- + \text{H}^+\)

Strength Comparison:

Phenols are more acidic than alcohols because the conjugate base (phenoxide ion) is resonance-stabilized, spreading the negative charge over the aromatic ring. This increased stability makes it easier for phenols to lose a proton. Alcohols are less acidic because their conjugate base (alkoxide ion) lacks such resonance stabilization.

 Bronsted Bases:

Bronsted Base Definition:

A Bronsted base is a substance that can accept a proton \((H^+)\). Alcohols and phenols can also accept protons due to the lone pairs on the oxygen atom, acting as Bronsted bases.

Primary Acidic Behavior in Context

In the context of acidity, the ability of alcohols and phenols to donate a proton is more relevant. This property defines them primarily as Bronsted acids. Their role as Bronsted bases is secondary when focusing on their acidic properties.

Conclusion: Given their ability to donate protons, alcohols and phenols are primarily classified as Bronsted acids: Bronsted basas