CBSE Class 12 Chemistry Ch 7 - Alcohols, Phenols, and Ethers Notes

Alcohols, Phenols, and Ethers can seem intimidating at first glance — but with the right guidance, it becomes one of the most scoring chapters in Class 12 Chemistry. In this guide, we’ve simplified all class 12 Chemistry chapter 7 Alcohols, Phenols, and Ethers notes–from physical properties to important chemical reactions.

Whether you’re cramming last–minute or just revising smartly, these Class 12 Chemistry Chapter 7 notes will help you grasp everything faster, without rote learning.

Alcohols, Phenols, and Ethers Summary

If you're staring at those long chemistry chapters and feeling a little lost – we’ve got your back. From “What is ether?” to “Do we really need to know all these reactions?” – this blog breaks it all down in a simple, non–boring way.

What Are Alcohols?

They are indicated by the presence of an -OH group in a chain. This -OH is regarded as a hydroxyl group.

• The functional group is -OH (hydroxyl).
• The suffix for naming is “–ol” (e.g., methanol, ethanol).

 Examples: Methanol (CH₃OH), Ethanol (C₂H₅OH), Propanol (C₃H₇OH)

Types of Alcohols – Primary, Secondary, Tertiary

1) On the basis of the number of -OH (hydroxyl) groups attached, there are three types of alcohol. 

•  Monohydric alcohols: one -OH group (e.g., CH₃OH, C₂H₅OH)
•  Dihydric alcohols: two -OH groups (e.g., ethylene glycol)
•  Polyhydric alcohols: three or more -OH groups (e.g., glycerol)

2) On the basis of alpha carbon (primary, secondary, tertiary alcohols)

Alcohols – Structure & Bonding Explained

Oxygen in alcohol is sp³‑hybridised, forming a roughly tetrahedral shape. The C–O–H bond angle in methanol is ~108.9°, slightly greater than 104.5° in water, due to lone pair repulsion

How to Prepare Alcohols? – Class 12 Chemistry Guide

You’ll see alcohols being made from alkenes, aldehydes, ketones, acids, and more. Here are the main ways to make alcohol.

1. From Alkenes

• Acid–catalysed hydration: Alkene + H₂O (with H₂SO₄) → Alcohol
• Hydroboration–oxidation: BH₃ + H₂O₂/NaOH → Alcohol (anti–Markovnikov)

2. From Aldehydes & Ketones (by reduction)

• Aldehyde → Primary alcohol
• Ketone → Secondary alcohol
• Reagents: NaBH₄ or LiAlH₄

3. From Carboxylic Acids / Esters

• Strong reduction using LiAlH₄
• Always gives primary alcohols

4. From Alkyl Halides

• Alkyl halide + aqueous KOH/NaOH → Alcohol + halide salt

5. Using Grignard Reagents (RMgX) with:

• Formaldehyde → 1° alcohol
• Aldehyde → 2° alcohol
• Ketone → 3° alcohol

Final step: Add H₂O to complete

6. By Fermentation

• Glucose + yeast (anaerobic) → Ethanol + CO₂

Physical Properties of Alcohols – Quick Revision for Class 12

Here’s what you really need to know about how alcohols behave:

• State: Lower alcohols (like methanol, ethanol) are liquids at room temp. Higher ones can be oily or solid.
• Boiling Point: High, thanks to strong hydrogen bonding between -OH groups. Much higher than alkanes of similar size.
• Solubility in Water: Short–chain alcohols (like ethanol, methanol) mix well with water. As the carbon chain grows longer, solubility drops.
• Density: Alcohols are mostly less dense than water – so yes, they float!
• Smell: Most have a sharp, often sweet or medicinal smell (especially ethanol and isopropanol).
• Acidity: Alcohols are weakly acidic. They can react with metals like sodium to give hydrogen gas and form alkoxides.
• Polarity: Due to the -OH group, alcohols are polar and can form hydrogen bonds – that’s why they dissolve in water easily (at least the smaller ones).

Chemical Reactions of Alcohols – Must–Know Class 12 Important Reactions

Alcohols may look innocent, but they’re super reactive in the lab. Let’s break it down:

• Combustion: Alcohols burn in oxygen to give carbon dioxide and water. That’s why ethanol can be used as fuel.
• Oxidation (Primary Alcohols): First turns into aldehydes → then to carboxylic acids if oxidation continues.
• Oxidation (Secondary Alcohols): Converts into ketones. That’s it. No further oxidation.
• Tertiary Alcohols: Pretty stubborn – they don’t oxidize easily unless under very strong conditions.
• Dehydration: Remove water using heat + acid, and alcohol becomes an alkene (double bond alert!).
• Esterification: Mix an alcohol with a carboxylic acid + a little H₂SO₄ → boom, you get a sweet–smelling ester.
• Reaction with Metals: Alcohol reacts with metals like sodium to release hydrogen gas (bubbling test!) and forms alkoxides.
• Nucleophilic Substitution: The -OH group gets swapped out for halogens using reagents like PCl₅, SOCl₂, or Lucas reagent.
• Ether Formation: Two alcohols join hands (under acid and heat) to form an ether + water.

Lucas Test:

Purpose: To distinguish between primary, secondary, and tertiary alcohols based on how fast they react with Lucas reagent (HCl + ZnCl₂).

What happens: The alcohol reacts with Lucas reagent and forms a cloudy layer (turbidity) due to formation of an alkyl chloride.

Result Based on Type of Alcohol:

• Primary Alcohol
  1. No visible change at room temp
  2. Needs heating to react (very slow)
• Secondary Alcohol
  Turbidity appears in 5–10 minutes
• Tertiary Alcohol
  Turbidity appears immediately

Why this happens: Tertiary alcohols form stable carbocations fastest → react quickly. Primary ones form unstable carbocations → slow/no reaction at room temp.

Reactions of Alcohols 

a)  Reaction with Phosphorus Halides (PCl₅, PCl₃, etc.)

• Alcohol + Phosphorus halide → Alkyl halide + side products
• Example: CH₃CH₂OH + PCl₅ → CH₃CH₂Cl + POCl₃ + HCl
• This reaction replaces the -OH group with a halogen (Cl, Br, etc.)

b)  Reaction with Thionyl Chloride (SOCl₂)

• Alcohol + SOCl₂ → Alkyl chloride + SO₂ + HCl (all gases)
• Very useful because side products escape as gases = clean reaction
• Example: CH₃CH₂OH + SOCl₂ → CH₃CH₂Cl + SO₂ + HCl
  
  

c) Dehydration of Alcohols to Form Alkenes

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• In presence of conc. H₂SO₄ or alumina (Al₂O₃) and heat
• Alcohol loses water (H₂O) → forms alkene
• Example: CH₃CH₂OH → CH₂=CH₂ + H₂O (with heat & acid)

What are Phenols? – Strong Smell, Stronger Reactions!

Phenols are organic compounds where an -OH group is directly attached to an aromatic ring (like benzene). Unlike alcohols, phenols are slightly acidic and have unique reactions because of this setup.

Think of them as the fancier cousins of alcohols – more reactive, more interesting, and a bit more dramatic in chemistry questions.

Classification of Phenols

Let’s break it down based on how many -OH groups are attached to the ring:

1. Monohydric Phenols

 → Only one -OH group

 → Example: Phenol (the OG one)

2. Dihydric Phenols

 → Two -OH groups on the ring

 → Examples:

• Catechol (-OH at 1,2 positions)
• Resorcinol (-OH at 1,3 positions)

3. Trihydric Phenols

 → three -OH groups.

 → Example: Pyrogallol (-OH at 1,2,3 positions)

That’s literally it. Once you get this, the rest of the chapter becomes way easier to follow.

Structure of Phenols:

• Basic Structure: Phenol = Benzene ring + Hydroxyl group (-OH).
• Position: The -OH group is directly attached to the aromatic benzene ring.
• Bonding: The oxygen in -OH is sp² hybridized and forms a strong hydrogen bond.
• Electron Movement: The lone pair on the oxygen interacts with the benzene ring’s π–electrons – this gives resonance, making the -OH group a bit acidic.
• Resonance Effect: The electrons from oxygen delocalize into the ring → this makes phenol more stable than it looks.
• Acidic Nature: Due to this structure + resonance, phenols are more acidic than alcohols.

TL;DR: Phenol’s -OH isn’t just hanging there – it’s bonded to a benzene ring and takes part in resonance. That’s why it reacts differently from normal alcohols.

Preparation of Phenols:

Here are the main methods to prepare phenols – simple, to the point:

(1) From Haloarenes (Chlorobenzene Method)

When chlorobenzene is fused with NaOH at high temperature and pressure, it forms sodium phenoxide, which is then acidified to get phenol.
Reaction:
C₆H₅Cl + NaOH → C₆H₅ONa + NaCl
C₆H₅ONa + HCl → C₆H₅OH (Phenol)

(2) From Benzene Sulphonic Acid

When benzene sulphonic acid is fused with NaOH at high temperatures, it forms sodium phenoxide, which is then acidified to get phenol.

Reaction: C₆H₅SO₃Na + NaOH → C₆H₅ONa + Na₂SO₃
C₆H₅ONa + HCl → C₆H₅OH (Phenol)

(3) From Diazonium Salts

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Benzenediazonium chloride reacts with warm water to give phenol.

Reaction: C₆H₅N₂⁺Cl⁻ + H₂O → C₆H₅OH + N₂ + HCl

(4) From Cumene (Industrial Method)

This is the one used in industries. Cumene is oxidised to cumene hydroperoxide, which breaks down in acid to give phenol.

Reaction: Cumene → Cumene hydroperoxide → Phenol + Acetone

Physical Properties of Phenols

Phenols look simple, but they behave differently from regular alcohols. Here’s a quick breakdown:

• State: Most phenols (like simple phenol) are solid at room temperature.
• Smell: They have a sharp, antiseptic–like smell – that's why they’re often used in disinfectants.
• Solubility: Phenols are partially soluble in water. The -OH group helps them dissolve, but the bulky benzene ring resists – so it’s a mix.
• Boiling Point: Higher than alcohols of similar size. That’s due to strong hydrogen bonding between molecules.
• Colour on Storage: Pure phenol is white, but it can turn pinkish or reddish on standing – thanks to slow oxidation in air.

So, even though they look like alcohols, phenols act a bit different, especially in terms of acidity and reactions

Chemical Reactions of Phenols

Phenols show both electrophilic substitution and acidic reactions; they're way more reactive because of that -OH group directly attached to an aromatic ring. Let’s break down their main reactions that you must know for your Class 12 board exam:

(i) Electrophilic Substitution Reactions

Phenol’s benzene ring becomes super active (especially at ortho and para positions) due to the electron–donating -OH group. That’s why it easily undergoes the following:

(a) Nitration:
When treated with dilute HNO₃, phenol forms a mix of:

• O–nitrophenol
• P–nitrophenol (Use cold, dilute nitric acid to avoid overreaction)

(b) Halogenation:
Phenol reacts with bromine water to form a white precipitate of:
2,4,6–tribromophenol
(This happens without needing a catalyst, thanks to phenol’s reactivity)

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(c) Sulphonation:
When heated with concentrated H₂SO₄, phenol gives:

• o–hydroxybenzene sulphonic acid
• p–hydroxybenzene sulphonic acid
  (The major product depends on temperature)

(ii) Reimer–Tiemann Reaction

This is a special reaction where phenol reacts with chloroform (CHCl₃) and NaOH, forming salicylaldehyde (–CHO group comes at ortho position). It’s a super important reaction, often asked in exams.

(iii) Kolbe’s Reaction

Phenol reacts with sodium hydroxide and CO₂ under heat and pressure, forming salicylic acid – the same stuff used to make aspirin!

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Functional group added: –COOH at ortho position.

(iv) Acidic Nature of Phenol

Phenol is more acidic than alcohols because its phenoxide ion is stabilized by resonance.

• Reacts with NaOH → Sodium phenoxide (soluble)
• Does not react with weaker bases like Na₂CO₃ (unlike carboxylic acids)

Tests to distinguish alcohol and phenol:

• Litmus test: Phenol turns blue litmus red
• Azo dye: Phenol → orange; alcohol → no reaction
• Br₂ water: Phenol → white ppt; alcohol → no ppt

What are Ethers? – The Quiet Ones in the Group

Ethers are the organic compounds in which two alkyl or aryl groups are attached to a divalent oxygen. These are represented by the general formula R–O–R.

Nomenclature: In the IUPAC system, ethers are regarded as ‘alkoxy alkanes' in which the ethereal oxygen is taken along with a smaller alkyl group while the bigger alkyl group is regarded as a part of the alkane.

Preparation of Ethers

Ethers are commonly prepared using two main methods. Here’s the simple, no–confusion version:

1. Williamson’s Synthesis – The Go–To Method

This one’s super important and very common in exams.

How it works:
React a sodium alkoxide (RO⁻ Na⁺) with a primary alkyl halide (R–X).

Reaction:

R–O⁻ Na⁺ + R'–X → R–O–R' + NaX

Example:

CH₃ONa + CH₃CH₂Br → CH₃–O–CH₂CH₃ (Ethyl methyl ether)

Works best with primary halides.
Avoid tertiary halides – they’ll give elimination instead of substitution.

2. Dehydration of Alcohols (Lab Method)

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Good for making symmetrical ethers like diethyl ether.

How it works:
Heat excess alcohol with concentrated H₂SO₄ at 443 K.

Reaction:
2CH₃CH₂OH → CH₃CH₂–O–CH₂CH₃ + H₂O

Happens via protonation, carbocation formation, and nucleophilic attack.

Physical Properties of Ethers

Ethers might look simple, but their properties are super important to understand – especially for MCQs and comparison questions.

1. Boiling Point

• Ethers have low boiling points compared to alcohols of similar molecular mass.
• Why? Because ethers can’t form hydrogen bonds with themselves, unlike alcohols.
• But their boiling point is still higher than alkanes – thanks to the presence of the oxygen atom.

Quick example:  Ethanol (alcohol) > Diethyl ether > Butane (alkane)

2. Solubility

• Ethers can form hydrogen bonds with water (thanks to the oxygen lone pairs), so lower ethers are water soluble.
• However, as the carbon chain increases, solubility drops (non–polar part increases).

3. Polarity

• Ethers are polar due to the oxygen atom.
• But they’re still less polar than alcohols.

4. Odour & State

• Most ethers are colorless liquids with a sweet smell.
• Some are even used as anesthetics (like diethyl ether).

Reminder: Ethers don’t form hydrogen bonds with themselves – so lower b.p. than alcohol

‍Chemical Reactions of Ethers

Let’s take a look at how ethers behave chemically.

1. Acidic Cleavage (with HI or HBr)

This is the most important reaction to remember!

Reaction: ‍

Conditions:

• Reagent: Conc. HI or HBr
• Heat is applied
• Excess acid ensures full cleavage

Example:
Diethyl ether + HI → Ethyl iodide + Ethanol
(Ethanol then also gets converted to ethyl iodide if more HI is present)

2. Reaction with Oxygen (Peroxide Formation)

• Ethers react slowly with oxygen from air to form explosive peroxides.
• That’s why old ether bottles are risky and must be stored carefully.

No need to write the full reaction here for boards, just remember: peroxide formation = dangerous!

3. Electrophilic Substitution (on Aromatic Ethers)

• In aromatic ethers like anisole (methoxybenzene), the –OCH₃ group is electron–donating.
• So reactions like nitration, halogenation, sulphonation happen at ortho and para positions.

Example:

Uses of Ethers

Here are some of the uses of ethers:

1. Used as Solvents in Labs

Ethers like diethyl ether are awesome solvents. Why? Because they’re not reactive with most compounds. So, they’re used in labs for reactions where we don’t want the solvent interfering. Due to their relatively low reactivity, ethers serve as ideal solvents in lab reactions where interference must be minimized.

2. Used in Medicine (as Anesthetics)

Back in the day, ether was used as a surgical anesthetic – it helped people sleep through operations. It’s not used as much now because of better options, but its legacy in medicine is strong.

3. Used in Perfumes and Cosmetics

Some ethers have a pleasant smell, making them useful in perfumes. They also show up in cosmetic products because they evaporate easily and feel light on the skin.

4. Used in Fuel and Oil Industry

Certain ethers like MTBE (Methyl tert–butyl ether) are added to petrol to help it burn better and reduce pollution. Yup, ethers help your vehicle run smoother.

Alcohols, Phenols, and Ethers – Summary of Key Reactions

Here’s a summary of the above information.

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Conclusion 

Alcohols, phenols, and ethers might look similar in structure, but their reactions, acidity, and real–world importance are super different. If you get the hang of their preparation, properties, and how they behave in reactions.

By understanding the logic behind their preparation methods and chemical behavior, you can score full marks in this Class 12 Chemistry Chapter. Keep revising the key reactions, use tricks like the Lucas test for quick identification, and focus on previous year questions.

Frequently Asked Questions

Q1. What is the difference between alcohol and phenols?

Ans: Alcohols have –OH groups attached to aliphatic carbon atoms, while phenols have –OH attached to aromatic rings. Phenols are more acidic and undergo different types of reactions due to resonance.

Q2. What is the Lucas Test and what does it detect?

Ans: Lucas Test distinguishes between 1°, 2°, and 3° alcohols based on turbidity when reacted with Lucas reagent (HCl + ZnCl₂). Tertiary alcohols turn cloudy immediately.

Q3. Which reaction is used to prepare phenol industrially?

Ans: The Cumene process is the industrial method. Cumene is oxidized to cumene hydroperoxide, which is then acidified to give phenol and acetone.

Q4. Why do ethers have low boiling points compared to alcohols?

Ans: Ethers can't form hydrogen bonds with themselves, unlike alcohols, which is why their boiling point is lower despite similar molecular mass.

Q5. Which is the most important reaction of ethers for the board exam?

Ans: Acidic cleavage using HI or HBr is most important. It breaks ethers into alcohols and alkyl halides