Class 12 Chemistry Alcohols, Phenols And Ethers Complete Notes by PW

Alcohols, Phenols and Ethers is an important chapter in Class 12 Chemistry, covering the preparation, properties and reactions of these organic compounds. Understanding reaction mechanisms, named reactions, and important conversions is essential for solving application-based and board exam questions. Regular revision of NCERT concepts and practice questions can also help strengthen your preparation.

PW brings you complete chapter notes for this chapter, covering key concepts and board-oriented questions for CBSE Class 12. Along with notes, PW provides video lectures, online batches and other learning resources to help you understand reactions, practise conversions and prepare for the 2027 board examination.

Basic Definitions And Structures

The hydroxyl group is represented by -OH.

The carbon attached to -OH is:

• sp3 hybridised in alcohols.

• sp2 hybridised in phenol.

Memory Tip: Alcohol has -OH on an aliphatic carbon; phenol has -OH directly on benzene; benzylic alcohol has -OH on a carbon connected to benzene; allylic alcohol has -OH next to a double bond; vinylic alcohol has -OH directly on a double-bonded carbon.

Classification Of Alcohols

Based on the number of hydroxyl groups:

• Monohydric alcohol: One -OH group

• Dihydric alcohol: Two -OH groups

• Trihydric alcohol: Three -OH groups

• Polyhydric alcohol: Many -OH groups

Based on the carbon bearing -OH:

• Primary alcohol: The carbon is attached to one other carbon.

• Secondary alcohol: The carbon is attached to two other carbons.

• Tertiary alcohol: The carbon is attached to three other carbons.

The degree of an alcohol is always determined by the carbon directly attached to -OH.

Allylic, Benzylic And Vinylic Alcohols

• Allylic alcohol: -OH is attached to an sp3 carbon next to a double bond.

• Benzylic alcohol: -OH is attached to a carbon connected to a benzene ring, but not directly to the ring.

• Vinylic alcohol: -OH is attached directly to an sp2 carbon involved in a double bond.

Nomenclature Of Alcohols, Phenols And Ethers

The general naming order is:

Word Root → Primary Suffix → Secondary Suffix → Primary Prefix → Secondary Prefix

The word root shows the number of carbon atoms. The primary suffix shows bonding:

• Single bond: -ane

• Double bond: -ene

• Triple bond: -yne

For alcohol, the secondary suffix is -ol. Numbering starts from the end nearest to the hydroxyl group.

Examples:

• Three-carbon chain with -OH at carbon 1: propan-1-ol

• Four-carbon chain with -OH at carbon 2: butan-2-ol

• Methyl group at carbon 2 and -OH at carbon 1: 2-methylbutan-1-ol

When alcohol is not the senior functional group, it is written as the prefix hydroxy-. For example, a compound containing carboxylic acid and alcohol is named using -oic acid for the acid and hydroxy- for the alcohol.

Phenol Nomenclature

The benzene ring with a directly attached -OH is named phenol. The carbon bearing -OH is carbon 1.

• Bromine at carbon 2: 2-bromophenol

• Bromine at carbon 3: 3-bromophenol

• Bromine at carbon 4: 4-bromophenol

Ether Nomenclature

Ethers are named as alkoxyalkanes.

• Smaller group: Alkoxy prefix

• Larger group: Parent alkane

Examples:

• CH3-O-CH3: methoxymethane

• CH3-O-CH2CH3: methoxyethane

• CH3-O-CH2CH2CH3: methoxypropane

Memory Tip: Smaller carbon group becomes the alkoxy prefix, while the larger carbon group becomes the parent alkane.

Preparation Of Alcohols

Hydration Of Alkenes

Hydration is the addition of water to a double bond.

• Acid-catalysed hydration follows Markovnikov’s rule.

• Hydroboration-oxidation follows the anti-Markovnikov rule.

In Markovnikov addition, OH goes to the double-bonded carbon with fewer hydrogen atoms. In anti-Markovnikov addition, OH goes to the carbon with more hydrogen atoms.

Memory Tip: Markovnikov means OH on the carbon with fewer H atoms; anti-Markovnikov means OH on the carbon with more H atoms.

From Haloalkanes

Haloalkanes react with aqueous sodium hydroxide:

R-X + OH- → R-OH + X-

With aqueous hydroxide, the reaction generally follows the SN2 pathway and gives inversion of configuration. Reaction with water may follow SN1, involving a carbocation and a mixture of inversion and retention.

Using Grignard Reagents

Grignard reagents have the formula RMgX and react with carbonyl compounds followed by hydrolysis.

• Formaldehyde: Produces a primary alcohol.

• Aldehyde other than formaldehyde: Produces a secondary alcohol.

• Ketone: Produces a tertiary alcohol.

Reduction

• Aldehyde reduction gives a primary alcohol.

• Ketone reduction gives a secondary alcohol.

• Carboxylic acid reduction with LiAlH4 gives a primary alcohol.

Common reducing agents include LiAlH4, NaBH4, and catalytic hydrogenation using H2 with Ni, Pt, or Pd.

Preparation Of Phenol

Important methods include:

1. From haloarenes: Chlorobenzene reacts with NaOH at about 623 K to form sodium phenoxide. Acidification with HCl gives phenol.

2. From diazonium salts: Benzene diazonium chloride reacts with warm water to produce phenol, nitrogen, and HCl.

3. From benzene sulphonic acid: Treatment with NaOH forms sodium phenoxide, which gives phenol on acidification.

4. From cumene: Cumene is oxidised by air to cumene hydroperoxide. Heating produces phenol and acetone.

Preparation Of Ethers

Dehydration Of Alcohols

With concentrated H2SO4:

• At approximately 413 K, two alcohol molecules form an ether.

• At approximately 443 K, one alcohol molecule forms an alkene.

Williamson Ether Synthesis

Sodium alkoxide reacts with a primary alkyl halide:

RONa + R-X → R-O-R + NaX

This reaction follows the SN2 mechanism. Primary alkyl halides are preferred because secondary and tertiary halides favour elimination and alkene formation.

Physical Properties

Boiling Point

The general order is:

Carboxylic acids > Alcohols > Aldehydes and ketones > Ethers > Hydrocarbons

Alcohols have high boiling points because they form hydrogen bonds. Ethers are polar but do not form comparable intermolecular hydrogen bonding. Boiling point increases with molecular mass and decreases with branching.

Solubility

Lower alcohols are highly soluble in water because their hydroxyl groups form hydrogen bonds with water. Solubility decreases as the carbon chain becomes longer because the hydrophobic part increases.

Chemical Properties Of Alcohols

Alcohols can act as nucleophiles or electrophiles.

Acidity

Alcohols donate the hydrogen of the hydroxyl group. Their conjugate-base stability controls acidity.

The important acidity order is:

Phenol > Water > Ethanol

Phenoxide ion is stabilised by resonance. The alkyl group in ethanol has a +I effect, which decreases acidity.

Higher acidity means higher Ka and lower pKa.

Esterification

Alcohols react with carboxylic acids, acid anhydrides, or acyl chlorides to form esters.

ROH + RCOOH → RCOOR + H2O

The preparation of aspirin from salicylic acid is an acetylation reaction involving the phenolic hydroxyl group.

Reactions With Metals

Alcohols and phenols react with sodium to form alkoxides or phenoxides and hydrogen gas. Phenol also reacts with NaOH to form sodium phenoxide.

Conversion To Haloalkanes

Important reagents include:

• PCl3: Produces alkyl chloride and H3PO3.

• PCl5: Produces alkyl chloride, POCl3, and HCl.

• SOCl2: Produces alkyl chloride, SO2, and HCl.

The SOCl2 method is preferred for preparing pure haloalkanes because gaseous by-products escape.

Lucas Test

Lucas reagent contains concentrated HCl and anhydrous ZnCl2.

Oxidation

• Primary alcohol + mild oxidant → Aldehyde

• Primary alcohol + strong oxidant → Carboxylic acid

• Secondary alcohol → Ketone

• Tertiary alcohol → Alkene under suitable conditions

PCC is used for converting a primary alcohol to an aldehyde. KMnO4, K2Cr2O7, and Jones reagent can oxidise it further to a carboxylic acid.

Chemical Properties Of Phenol

Nitration

• Dilute HNO3 gives ortho- and para-nitrophenol.

• Concentrated HNO3 gives 2,4,6-trinitrophenol, commonly called picric acid.

Bromination

Bromine in a solvent gives ortho- and para-bromophenol. Bromine water gives substitution at all three available ortho and para positions.

Kolbe Reaction

Sodium phenoxide reacts with CO2 on heating to form salicylic acid through ortho substitution.

Reimer-Tiemann Reaction

Phenol reacts with CHCl3 and aqueous NaOH to produce salicylaldehyde through ortho substitution.

Phenol heated with zinc dust gives benzene.

Chemical Properties Of Ethers

Ethers undergo cleavage with hydrogen halides:

Anisole undergoes bromination, nitration, Friedel-Crafts alkylation, and Friedel-Crafts acylation mainly at the ortho and para positions because the -OCH3 group is ortho- and para-directing.

Prepare Class 12 Chemistry Chapter 7 with this one-shot lecture by PW. The session covers important NCERT-based concepts, reactions, mechanisms and board-oriented questions to support your CBSE Class 12 Board Exam 2027 preparation.

What is covered in the video?

• Classification and Nomenclature

• Preparation of Alcohols, Phenols and Ethers

• Physical and Chemical Properties

• Important Reactions of Alcohols

• Important Reactions of Phenols

• Important Reactions of Ethers

• Mechanisms of Important Reactions

• Named Reactions

• Important Conversions

• NCERT-Based Questions

• Previous Year Questions (PYQs)

• Board Exam-Oriented Questions

A clear understanding of reactions, mechanisms and conversions is important for preparing for Alcohols, Phenols and Ethers. Revise the NCERT concepts, practise important questions and revisit reactions regularly to strengthen your preparation. PW's one-shot lecture, notes, online batches and other learning resources can help you revise this chapter and prepare for the CBSE Class 12 Board Exam 2027.