Phenols
Acidity, electrophilic substitution and important reactions such as Reimer–Tiemann and Kolbe. (Chemistry › Alcohols, Phenols and Ethers, NEET UG syllabus.)
What is Phenols?
An organic compound in which a hydroxyl group (-OH) is directly attached to an aromatic hydrocarbon ring.
Key points
- Explain the acidic nature of phenols and compare it with alcohols and carboxylic acids.
- Draw resonance structures of phenol and phenoxide ion to justify their properties.
- Predict the products of electrophilic aromatic substitution reactions of phenol (nitration, halogenation, sulphonation).
- Describe the mechanism and products of Kolbe's reaction.
Common exam trap
Confusing the acidity of phenols with that of alcohols or carboxylic acids.
Definitions
- Term
Phenol
- Meaning
An organic compound in which a hydroxyl group (-OH) is directly attached to an aromatic hydrocarbon ring.
- Term
Phenoxide ion
- Meaning
The conjugate base of phenol, formed by the deprotonation of the hydroxyl group, stabilized by resonance with the aromatic ring.
- Term
Electrophilic Aromatic Substitution
- Meaning
A type of organic reaction in which an atom (usually hydrogen) attached to an aromatic system is replaced by an electrophile.
- Term
Kolbe's Reaction
- Meaning
A carboxylation reaction that converts sodium phenoxide into salicylic acid by reacting with carbon dioxide under specific conditions, followed by acidification.
- Term
Reimer-Tiemann Reaction
- Meaning
A chemical reaction used for the ortho-formylation of phenols, typically involving the reaction of phenol with chloroform in the presence of a strong base to form salicylaldehyde.
Learning objectives
Explain the acidic nature of phenols and compare it with alcohols and carboxylic acids.
Draw resonance structures of phenol and phenoxide ion to justify their properties.
Predict the products of electrophilic aromatic substitution reactions of phenol (nitration, halogenation, sulphonation).
Describe the mechanism and products of Kolbe's reaction.
Describe the mechanism and products of Reimer-Tiemann reaction.
Identify the reagents and conditions for important reactions of phenols.
Prerequisites
Basic understanding of organic nomenclature and functional groups.
Knowledge of resonance structures and their effect on stability.
Concepts of acidity and basicity in organic chemistry.
Fundamentals of electrophilic aromatic substitution reactions.
Understanding of reaction mechanisms and intermediates.
Common mistakes
Confusing the acidity of phenols with that of alcohols or carboxylic acids.
Incorrectly identifying the directing effect of the -OH group in electrophilic substitution.
Forgetting the specific reagents and conditions for Kolbe's and Reimer-Tiemann reactions.
Mixing up the products of Kolbe's (salicylic acid) and Reimer-Tiemann (salicylaldehyde) reactions.
Not understanding the role of resonance in stabilizing the phenoxide ion.
Keywords
Phenol
Acidity
Phenoxide
Resonance
Electrophilic Substitution
Kolbe Reaction
Reimer-Tiemann Reaction
Salicylic Acid
Salicylaldehyde
Ortho/Para Directing
Activating Group
Nitration
Halogenation
Practice preview
Why are phenols more acidic than alcohols?…
easy
Which of the following compounds is the most acidic?…
medium
The Reimer-Tiemann reaction of phenol with chloroform in the presence of sodium hydroxide followed by hydrolysis yields:…
medium