Alcohols, Phenols and Ethers Complete Revision for CUET 2027 and Class 12 Chemistry

Alcohols, phenols and ethers can be challenging to revise because their preparation methods, acidity, chemical properties and reactions differ despite containing oxygen. Remembering reaction conditions, identifying products and distinguishing between named reactions can make this Class 12 Chemistry chapter difficult, especially when preparing for CUET 2027.

Physics Wallah helps you revise these concepts through its Class 12 Chemistry and CUET 2027 revision resource. Reviewing functional groups, nomenclature, preparation methods, chemical properties and named reactions can help you understand the differences between alcohols, phenols and ethers and recall important reactions more confidently in the examination.

Basic Definitions and Nomenclature

Alcohols, phenols and ethers are classified by their functional groups, which determine their naming rules, structures and chemical properties.

Alcohols

Alcohols contain a hydroxyl group (–OH) attached to an sp³-hybridised carbon atom. Their IUPAC names generally use the suffix -ol.

When the hydroxyl group is treated as a substituent because another functional group has naming priority, the prefix hydroxy- is used.

Alcohols are classified by the number of hydroxyl groups they contain:

• Monohydric: One –OH group

• Dihydric: Two –OH groups

• Trihydric: Three –OH groups

• Polyhydric: Multiple –OH groups

Glycerol is a trihydric alcohol with three hydroxyl groups.

Phenols

Phenols contain an –OH group directly attached to an aromatic ring, such as benzene. This distinguishes phenols from benzyl alcohol, where the –OH group is attached to a carbon outside the ring.

Ethers

Ethers contain an oxygen atom between two carbon-containing groups. Their general formula is R-O-R', where R and R′ may be identical or different.

 In IUPAC nomenclature, ethers are generally named as alkoxyalkanes. The smaller alkyl group forms the alkoxy substituent, while the larger group is chosen as the parent chain, following the naming rules covered in Class 12 Chemistry

Classification and Structure of Alcohols

Alcohols can be classified by the number of –OH groups and by the type of carbon attached to the hydroxyl group.

Classification by the carbon attached to –OH

Classification by position and hybridisation

Remember: Allylic and benzylic alcohols have –OH attached to an sp³ carbon, whereas vinylic alcohols have –OH attached directly to an sp² carbon.

Preparation of Alcohols

Alcohols can be prepared from haloalkanes, alkenes, carbonyl compounds and other organic compounds through specific reactions and conditions.

From haloalkanes

Haloalkanes react with aqueous alkali to form alcohols through nucleophilic substitution.

 R-X+OH-R-OH+X-

Depending on the substrate and reaction conditions, the reaction may follow an SN1 or SN2 mechanism.

From alkenes

Alkenes can form alcohols through hydration, which adds the elements of water across the double bond.

Using Grignard reagents

Grignard reagents react with carbonyl compounds, followed by acidic work-up, to form alcohols.

The carbon group supplied by the Grignard reagent becomes part of the new carbon–carbon bond.

By reduction of carbonyl compounds

Common reducing agents include lithium aluminium hydride (LiAlH₄) and, for suitable substrates, sodium borohydride (NaBH₄). These reductions connect with the reactions of Aldehydes, Ketones and Carboxylic Acids 

Preparation of Phenols and Ethers

Phenols and ethers are prepared through different reactions, including the conversion of haloarenes into phenols and Williamson ether synthesis for ethers.

Preparation of phenols

Important methods of phenol preparation include:

• From haloarenes: Chlorobenzene reacts with aqueous NaOH under high-temperature, high-pressure conditions to form sodium phenoxide, which gives phenol on acidification.

• From diazonium salts: Benzene diazonium chloride reacts with warm water to produce phenol.

• Cumene process: Cumene is oxidised to cumene hydroperoxide, which decomposes to form phenol and acetone.

• From benzene sulphonic acid: Fusion with NaOH produces sodium phenoxide, which forms phenol after acidification.

The exact conditions and intermediate products matter in reaction-based questions.

Preparation of ethers

Williamson ether synthesis is a key method for preparing ethers. An alkoxide ion reacts with a suitable alkyl halide to form an ether.

 RONa+R'XROR'+NaX

Primary alkyl halides generally work well in this reaction because the mechanism is usually SN2, whereas tertiary alkyl halides tend to undergo elimination instead. These outcomes depend on the substrate and the haloalkane reaction mechanisms. 

Dehydration of alcohols

Alcohols form different products depending on the reaction conditions.

The product also depends on the alcohol's structure. These temperatures are commonly taught as general Class 12 examination conditions, rather than universal rules for every alcohol.

Physical Properties of Alcohols, Phenols and Ethers

The physical properties of alcohols, phenols and ethers depend on factors such as hydrogen bonding, molecular mass and molecular structure, which influence their boiling points and solubility in water.

Boiling points

Alcohols generally have higher boiling points than ethers and comparable carbonyl compounds of similar molecular mass because alcohol molecules form intermolecular hydrogen bonds.

A useful general comparison is:

 Carboxylicacids>Alcohols>Aldehydesandketones

Ethers and hydrocarbons generally have lower boiling points than comparable alcohols, although the exact order depends on molecular mass and structure.

Solubility in water

Alcohols can form hydrogen bonds with water through their –OH groups. As the hydrocarbon chain becomes longer, the non-polar portion of the molecule becomes more significant, so water solubility generally decreases.

• Hydroxyl group: Promotes hydrogen bonding with water.

• Longer carbon chain: Generally reduces water solubility.

• Branching: Can affect solubility and boiling point.

Bond angle

The approximate C–O–C bond angle in ethers is around 111, while the C–O–H angle in alcohols is commonly given as around 109. Exact values vary with molecular structure.

Chemical Behaviour of Alcohols

Alcohols participate in reactions involving the O–H bond, the C–O bond, or both. The reaction depends on the reagent and conditions.

Acidity of alcohols

Alcohols can donate a proton to form an alkoxide ion:

ROH RO-+H+

Their acidity depends on the stability of the conjugate base. Alkyl groups generally show a positive inductive effect (+I), which can destabilise the negative charge on the alkoxide ion and reduce acidity.

Electron-withdrawing groups generally increase acidity by stabilising the conjugate base. Alcohols can also act as Brønsted bases by accepting a proton.

Important reactions of alcohols

For example, reaction with phosphorus pentachloride can be represented as:

 ROH+PCl5RCl+POCl3+HCl

Thionyl chloride (SOCl2) is often useful for converting alcohols into haloalkanes because the gaseous by-products, SO2 and HCl, can escape from the reaction mixture.

Lucas test

Lucas reagent contains concentrated HCl and anhydrous ZnCl2. It helps distinguish primary, secondary and tertiary alcohols based on the rate at which turbidity appears. Under typical test conditions, the general order of reaction rate is:

 3>2>1

Tertiary alcohols usually react fastest, while primary alcohols react much more slowly at room temperature.

Oxidation of alcohols

The product depends on the alcohol type and oxidising conditions.

PCC can oxidise primary alcohols to aldehydes under suitable conditions. Strong oxidising agents such as acidified potassium dichromate or potassium permanganate commonly oxidise primary alcohols further to carboxylic acids. When alcohol vapours pass over heated copper at approximately 573 K, primary alcohols form aldehydes and secondary alcohols form ketones through dehydrogenation. Tertiary alcohols may undergo dehydration to form alkenes.

Chemical Properties of Phenols

Phenols are more acidic than ordinary alcohols because the phenoxide ion formed after proton loss is stabilised by resonance.

Reactions with metals and zinc dust

• With sodium: Phenol forms sodium phenoxide and releases hydrogen gas.

• With zinc dust: Phenol forms benzene, with zinc oxide as a by-product.

Nitration of phenol

The –OH group activates the aromatic ring and directs electrophilic substitution mainly towards the ortho and para positions.

Bromination of phenol

• Bromine in a suitable non-polar solvent: Mainly ortho- and para-bromophenol.

• Bromine water: Forms 2,4,6-tribromophenol, observed as a white precipitate.

Kolbe reaction

In the Kolbe–Schmitt reaction, sodium phenoxide reacts with carbon dioxide under suitable conditions. Acidification produces salicylic acid, with substitution mainly at the ortho position through the named reactions and concepts. 

Reimer–Tiemann reaktion

Sodium phenoxide reacts with chloroform (CHCl3) and aqueous NaOH. After work-up, the major product is salicylaldehyde (2-hydroxybenzaldehyde).

Oxidation of phenol

Oxidation of phenol with suitable oxidising agents, such as acidified sodium dichromate, can produce benzoquinone.

Chemical Properties of Ethers

Ethers are generally less reactive than alcohols, but they undergo cleavage with strong hydrogen halides such as HI and HBr.

Cleavage of ethers

When an ether reacts with excess HI or HBr under suitable conditions, the C–O bond breaks to form an alcohol and a haloalkane initially. Further reaction may produce additional haloalkane, depending on the reagent and conditions.

Reactions of anisole

Anisole (C6H5OCH3) contains a methoxy group (–OCH₃) attached to a benzene ring. The methoxy group activates the ring and directs electrophilic substitution mainly towards the ortho and para positions.

The major product proportions depend on the reaction conditions and steric effects, reflecting the role of directing groups in electrophilic substitution reactions.

Alcohols, phenols and ethers become easier to revise when their functional groups, preparation methods and characteristic reactions are compared side by side. Focus on reaction conditions, product identification, acidity trends and named reactions rather than memorising isolated equations. Revisiting these concepts and practising chapter-based questions can support Class 12 Chemistry revision and CUET 2027 preparation.