Chapters

Everything NCERT Class 12 Unit 7 (Alcohols, Phenols and Ethers) says about alcohols and ethers that can be asked; phenols, the rest of the unit, are in their own file. JEE Main material beyond the book is marked Beyond NCERT. The short note stays for the last week; this is for a proper revision pass.

Formula sheet

Every order and rule in the chapter on one screen, for the last pass. Details and examples are in the sections below.

Rule	Order or result	Watch
Acid strength	H₂O > CH₃OH > 1° > 2° > 3°	Alkoxide is a stronger base than OH⁻
Boiling point	alcohol >> ether ≈ alkane of similar mass	H-bonding; branching lowers it
Reaction with HX	3° > 2° > 1°	Lucas: 3° at once, 1° not at room T
HX for ether cleavage	HI > HBr > HCl	Concentrated, hot
Ease of dehydration	3° > 2° > 1°	Via carbocation: watch for shifts
Ethanol + conc. H₂SO₄	443 K → ethene; 413 K → ethoxyethane
Acid hydration of alkene	Markovnikov	Can rearrange
Hydroboration–oxidation	anti-Markovnikov, no rearrangement	Looks like H₂O added "wrong way"
Grignard + carbonyl	HCHO → 1°; RCHO → 2°; ketone → 3°	Then H₃O⁺
Oxidation	1° → aldehyde → acid; 2° → ketone; 3° none	PCC stops at aldehyde
Cu, 573 K	1° → aldehyde; 2° → ketone; 3° → alkene
Williamson	RO⁻ + 1° R′X	3° halide gives only alkene
Ether + HI	1°/2°: smaller group → R–I (SN2)	3° group → 3° iodide (SN1); ArOR → ArOH + RI
Acetylation mass	+42 g mol⁻¹ per –OH	· Beyond NCERT

0 · What JEE Main asks from this chapter

52 questions in JEE Main 2019–2026, all MCQ, about 1 in every 3 papers. Grouped by type (counts are approximate):

Type	Share	Typical question
Making alcohols: hydration, hydroboration, Grignard, reduction	~22%	Propene → B₂H₆, H₂O₂ → PCC → CH₃MgBr → ? (2023)
Ether cleavage with HI or HBr	~20%	Cyclohexyl tert-butyl ether + HI → ? (2024)
Dehydration and carbocation shifts	~18%	3,3-Dimethylbutan-2-ol + conc. H₂SO₄ → ? (2021)
Tests and oxidation: Lucas, iodoform, PCC, Cu	~14%	C₃H₆O pair + CH₃MgBr; Lucas and iodoform results (2020)
Making ethers: Williamson, dehydration	~12%	Which Williamson pair fails? (2025)
Physical properties: boiling point, solubility	~10%	Highest b.p.: butane, butan-1-ol, butanal, ether (2024)
Others: epoxides, glycerol, cyclic ethers	~4%	Glycerol + KHSO₄ → acrolein (2022)

1 · Classification and nomenclature

Alcohols carry –OH on carbon of an aliphatic system; phenols on an aromatic carbon. By number of –OH: monohydric, dihydric, trihydric, polyhydric.

Class	–OH is on	Example
1°, 2°, 3°	sp³ C that is 1°, 2° or 3°	(CH₃)₃COH is 3°
Allylic	sp³ C next to C=C	CH₂=CH–CH₂OH
Benzylic	sp³ C next to a ring	C₆H₅CH₂OH
Vinylic	sp² C of C=C	CH₂=CH–OH
Phenol	sp² C of a ring	C₆H₅OH (see Phenols)

Allylic and benzylic alcohols can be 1°, 2° or 3°.

Ethers: simple (symmetrical) if both groups on O are the same (C₂H₅OC₂H₅); mixed (unsymmetrical) if not (C₂H₅OCH₃, C₂H₅OC₆H₅).

Naming alcohols (IUPAC): replace the "e" of the alkane with "ol"; number the longest chain from the end nearer –OH. For polyols keep the "e": HO–CH₂–CH₂–OH is ethane-1,2-diol. Cyclic: the –OH carbon is C-1 (2-methylcyclopentanol).

Structure	Common	IUPAC
CH₃CH₂CH₂OH	n-propyl alcohol	propan-1-ol
(CH₃)₂CHOH	isopropyl alcohol	propan-2-ol
CH₃CH₂CH(OH)CH₃	sec-butyl alcohol	butan-2-ol
(CH₃)₂CHCH₂OH	isobutyl alcohol	2-methylpropan-1-ol
(CH₃)₃COH	tert-butyl alcohol	2-methylpropan-2-ol
HOCH₂CH₂OH	ethylene glycol	ethane-1,2-diol
HOCH₂CH(OH)CH₂OH	glycerol	propane-1,2,3-triol

Naming ethers: common names list the two groups alphabetically + "ether" (ethylmethyl ether; diethyl ether). IUPAC: the larger group is the parent hydrocarbon, the smaller is alkoxy.

Structure	Common	IUPAC
CH₃OCH₃	dimethyl ether	methoxymethane
C₂H₅OC₂H₅	diethyl ether	ethoxyethane
CH₃OCH₂CH₂CH₃	methyl n-propyl ether	1-methoxypropane
(CH₃)₂CHOCH₃	methyl isopropyl ether	2-methoxypropane
C₆H₅OCH₃	anisole	methoxybenzene
C₆H₅OC₂H₅	phenetole	ethoxybenzene
C₆H₅O(CH₂)₆CH₃	heptyl phenyl ether	1-phenoxyheptane
CH₃OCH₂CH₂OCH₃	—	1,2-dimethoxyethane

2 · Structure

Molecule	C–O length	Angle at O
Methanol	142 pm	C–O–H 108.9°
Phenol	136 pm	C–O–H 109°
Methoxymethane	141 pm	C–O–C 111.7°

• Alcohols: O is sp³; the C–O–H angle is a little less than tetrahedral (109°28′) because O's two lone pairs repel.
• Ethers: the angle is a little more than tetrahedral because the two bulky R groups repel.
• Phenol's C–O is shorter: partial double-bond character from conjugation, and an sp² carbon.

3 · Preparation of alcohols

1. Acid-catalysed hydration of alkenes. Water adds with acid as catalyst, Markovnikov's way (H to the carbon with more H).

Mechanism, three steps:

1. The alkene is protonated by H₃O⁺ (electrophilic attack) to give a carbocation.
2. Water attacks the carbocation (nucleophilic).
3. Loss of H⁺ gives the alcohol.

Being a carbocation route, it can rearrange (Beyond NCERT: see section 5).

2. Hydroboration–oxidation (H. C. Brown, 1959). Diborane adds to the alkene to give a trialkylborane; H₂O₂ with aqueous NaOH oxidises it to the alcohol.

• Boron goes to the sp² carbon with more H, so the result looks like anti-Markovnikov addition of water.
• Excellent yield; no carbocation, so no rearrangement · Beyond NCERT.

Example (2024) · Propene + H₂O/H⁺ → propan-2-ol; propene + (BH₃)₂ then H₂O₂/OH⁻ → propan-1-ol.

3. Reduction of aldehydes and ketones: H₂ with finely divided Pt, Pd or Ni (catalytic hydrogenation), or NaBH₄ or LiAlH₄. Aldehydes → 1° alcohols; ketones → 2° alcohols.

4. Reduction of acids and esters: LiAlH₄ reduces RCOOH straight to RCH₂OH in excellent yield. LiAlH₄ is expensive, so industry first makes the ester, then reduces it with H₂ and a catalyst.

5. Grignard reagents with aldehydes and ketones. RMgX adds to C=O (nucleophilic addition) to give an adduct; hydrolysis gives the alcohol.

Carbonyl	Alcohol
HCHO (methanal)	1°, RCH₂OH
R′CHO (other aldehydes)	2°, R′CH(OH)R
R′COR″ (ketones)	3°, R′R″C(OH)R

Example (NCERT Example 7.2) · Catalytic reduction of butanal → butan-1-ol. Propene + dil. H₂SO₄ → propan-2-ol. Propanone + CH₃MgBr, then hydrolysis → 2-methylpropan-2-ol.

Example (2023) · Propene → B₂H₆, then H₂O₂/NaOH → propan-1-ol → PCC → propanal → CH₃MgBr, then H₃O⁺ → butan-2-ol.

Example (2024) · Styrene → BH₃, then H₂O₂/OH⁻ → PhCH₂CH₂OH → HBr → PhCH₂CH₂Br → Mg, ether, then HCHO, H₃O⁺ → PhCH₂CH₂CH₂OH (one carbon added).

Example (2020) · Two C₃H₆O compounds + CH₃MgBr. Propanal → butan-2-ol (2°: Lucas turbidity in about 5 min, iodoform positive). Propanone → 2-methylpropan-2-ol (3°: turbidity at once, iodoform negative).

Also from haloalkanes with aqueous KOH (Alkyl Halides). Ozonolysis of an alkene gives carbonyls, not alcohols (2023).

4 · Physical properties

• Boiling point rises with the number of C atoms (van der Waals) and falls with branching (smaller surface area).
• Alcohols boil far higher than hydrocarbons, ethers and haloalkanes of similar mass because of intermolecular H-bonding.

Compound (similar mass)	b.p.
Ethanol, C₂H₅OH	351 K
Methoxymethane, CH₃OCH₃	248 K
Propane, C₃H₈	231 K

• Solubility: alcohols H-bond with water. It falls as the alkyl (hydrophobic) part grows; the lower alcohols mix with water in all proportions.

Example (NCERT Example 7.3) · Increasing b.p.: methanol < ethanol < propan-1-ol < butan-2-ol < butan-1-ol < pentan-1-ol. And n-butane < ethoxyethane < pentanal < pentan-1-ol.

5 · Reactions of alcohols

Alcohols react both as nucleophiles (the O–H bond breaks; O attacks) and, once protonated, as electrophiles (the C–O bond breaks). True, but not explained by their reaction with sodium (2024).

O–H bond breaks

With active metals (Na, K, Al) → alkoxide + H₂:

Acidity: alcohols are Brønsted acids because the O–H bond is polar. An electron-releasing alkyl group puts more electron density on O and makes the O–H less polar. So:

• Alcohols are weaker acids than water: RO⁻ + H₂O → ROH + OH⁻. So an alkoxide is a stronger base than hydroxide (NaOC₂H₅ is stronger than NaOH).
• The lone pairs on O also make alcohols Brønsted bases (proton acceptors).
• Sodium dries ethers but not alcohols, which react with it (2025).

Esterification: with carboxylic acids or anhydrides (a little conc. H₂SO₄; reversible, so water is removed as it forms) or acid chlorides (with pyridine, which takes up the HCl and drives the reaction).

Putting a CH₃CO group on an –OH is acetylation.

Example (2026) · Compound X (122 g mol⁻¹) fully acetylated weighs 290 g mol⁻¹. Each –OH → –OCOCH₃ adds 42 (C₂H₂O). (290 − 122)/42 = 4 –OH groups.

C–O bond breaks (alcohols only; phenols only with Zn)

1. Hydrogen halides: R–OH + HX → R–X + H₂O, reactivity 3° > 2° > 1°.

Lucas test (conc. HCl + anhydrous ZnCl₂): the alcohol dissolves in the reagent, but its chloride doesn't, so turbidity appears.

Alcohol	Turbidity
3°	at once
2°	in about 5 minutes · timing Beyond NCERT
1°	none at room temperature

Ethanol does not turn turbid at once (2024).

2. Phosphorus halides and SOCl₂: PBr₃ gives alkyl bromides; PCl₃, PCl₅ and SOCl₂ give chlorides (Alkyl Halides, section 4).

3. Dehydration to alkenes with a protic acid (conc. H₂SO₄ or H₃PO₄) or a catalyst (anhydrous ZnCl₂, alumina).

Alcohol	Conditions
Ethanol (1°)	conc. H₂SO₄, 443 K → ethene
Propan-2-ol (2°)	85% H₃PO₄, 440 K → propene
2-Methylpropan-2-ol (3°)	20% H₃PO₄, 358 K → 2-methylpropene

Ease of dehydration: 3° > 2° > 1°, because a 3° carbocation forms most easily.

Mechanism (ethanol):

1. The alcohol is protonated: C₂H₅OH + H⁺ ⇌ C₂H₅OH₂⁺.
2. Water leaves to give the carbocation: slowest, rate-determining step.
3. A β-H⁺ is lost to give ethene.

The acid used in step 1 comes back in step 3. Ethene is removed as it forms, to drive the equilibrium.

Carbocation shifts and Saytzeff · Beyond NCERT · The carbocation in step 2 shifts H⁻ or CH₃⁻ to a more stable one when it can, and the more substituted alkene is the major product.

Example (2021) · 3,3-Dimethylbutan-2-ol + a few drops of conc. H₂SO₄: 2° cation → CH₃ shift → 3° cation → 2,3-dimethylbut-2-ene.

Example (2020) · Neopentyl alcohol (CH₃)₃CCH₂OH with acid: the 1° cation would be very poor, so a CH₃ shifts as water leaves → 2-methylbutan-2-yl cation → 2-methylbut-2-ene (85%) and 2-methylbut-1-ene (15%).

Example (2026) · Pentan-1-ol with conc. H₂SO₄ (or H₃PO₄) → pent-1-ene. The same reagent in excess on HOCH₂CH₂CH(OH)CH₃ removes both –OH → buta-1,3-diene.

4. Oxidation forms C=O by breaking O–H and C–H bonds; it is also called dehydrogenation.

Reagent	1° alcohol	2° alcohol
Acidified KMnO₄ (strong)	carboxylic acid directly	ketone
CrO₃, anhydrous	aldehyde	ketone
PCC (CrO₃ + pyridine + HCl)	aldehyde, good yield	ketone
Cu, 573 K (vapour)	aldehyde	ketone

• 3° alcohols don't oxidise. Under harsh conditions (KMnO₄, heat) C–C bonds break and a mixture of acids with fewer carbons forms.
• Over Cu at 573 K, a 3° alcohol is dehydrated to the alkene instead. tert-Butyl alcohol gives 2-methylpropene (2026).

Methanol poisoning (NCERT box): in the body methanol is oxidised to methanal, then methanoic acid, which can cause blindness and death. The treatment is intravenous diluted ethanol: it swamps the enzyme, giving the kidneys time to excrete the methanol.

Tests that tell alcohols apart · Beyond NCERT

• Iodoform (I₂ + NaOH → yellow CHI₃): positive for CH₃CH(OH)– alcohols (ethanol, propan-2-ol, butan-2-ol). Methanol and 1-propanol are negative.
• Ceric ammonium nitrate: red colour with any alcohol.
• Glycerol + KHSO₄, heat → acrolein (CH₂=CH–CHO), which has a pungent smell, not a fruity one (2022).

6 · Commercially important alcohols

Methanol ("wood spirit", once from destructive distillation of wood):

• Colourless liquid, b.p. 337 K, highly poisonous: small amounts cause blindness, large amounts death.
• Used as a solvent for paints and varnishes and, chiefly, to make formaldehyde.

Ethanol by fermentation of sugars:

• Sugar comes from molasses, sugarcane or fruit such as grapes; zymase comes from yeast.
• Fermentation is anaerobic (no air) and releases CO₂.
• Zymase stops working above about 14% alcohol.
• If air gets in, O₂ oxidises ethanol to ethanoic acid and spoils the taste.
• Colourless liquid, b.p. 351 K; a solvent in the paint industry and a starting material for many carbon compounds.
• Denatured alcohol: commercial alcohol made unfit to drink by adding copper sulphate (colour) and pyridine (foul smell).
• Large amounts now also come from the hydration of ethene.

7 · Preparation of ethers

1. Dehydration of alcohols. With H₂SO₄ or H₃PO₄ the product depends on conditions: ethanol at 443 K → ethene; at 413 K → ethoxyethane (ethanol in excess).

The ether forms by SN2: an alcohol molecule attacks a protonated alcohol.

• Works only for primary, unhindered alkyl groups, at low temperature. Otherwise the alkene wins.
• 2° and 3° alcohols give alkenes, not ethers: elimination beats substitution.
• Not for mixed ethers: methanol + ethanol would give a mixture of dimethyl, diethyl and ethyl methyl ethers (NCERT's question about ethyl methyl ether).

2. Williamson synthesis (Williamson, 1824–1904). An alkyl halide reacts with a sodium alkoxide. Good for both symmetrical and mixed ethers.

• It is SN2 attack of the alkoxide on the halide, so the halide must be primary. The alkoxide may be 2° or 3°.
• With a 2° halide elimination competes; with a 3° halide the alkene is the only product. Alkoxides are strong bases as well as nucleophiles.
• CH₃ONa + (CH₃)₃C–Br → only 2-methylpropene.
• Aryl ethers: use the phenoxide with an alkyl halide. Never an aryl halide with an alkoxide: aryl halides don't do SN2.

Example (NCERT Example 7.6) · C₂H₅ONa + (CH₃)₃CCl gives 2-methylprop-1-ene, not tert-butyl ethyl ether. The right pair: (CH₃)₃CONa + C₂H₅Br.

Example (2025) · Which pair fails? iso-BuO⁻Na⁺ + sec-BuBr: the 2° halide eliminates. The ones that work: cyclohexoxide + CH₃Br, PhO⁻ + n-PrBr, t-BuO⁻ + EtBr.

Example (2023, 2021) · Methyl phenyl ether: PhO⁻Na⁺ + CH₃Br. Ethyl phenyl ether by Williamson: yes, but not from bromobenzene + sodium ethoxide.

8 · Physical properties of ethers

• C–O bonds are polar, so ethers have a net dipole. The polarity is weak, so their boiling points are close to alkanes of similar mass and far below alcohols.

Compound	b.p.
n-Pentane	309.1 K
Ethoxyethane	307.6 K
Butan-1-ol	390 K

• Solubility is like that of alcohols of the same mass, because ether O can accept H-bonds from water: ethoxyethane 7.5 g and butan-1-ol 9 g per 100 mL; pentane hardly dissolves.
• Dimethyl ether is completely soluble in water; diethyl ether only a little (2025).

9 · Reactions of ethers

Ethers are the least reactive of the functional groups.

Cleavage by HX (concentrated, hot, excess; HI > HBr > HCl). A dialkyl ether gives two alkyl halide molecules in the end.

Mechanism (with HI):

1. The ether is protonated to an oxonium ion. Only HBr and HI are acidic enough.
2. I⁻ (a good nucleophile) attacks the less substituted carbon by SN2 and pushes out an alcohol.
3. With excess HI and heat, the alcohol also becomes an alkyl iodide.

Which group becomes the iodide:

Ether	Iodide	Alcohol
1° or 2° groups (CH₃OC₂H₅)	the smaller: CH₃I	C₂H₅OH
One group 3° ((CH₃)₃COCH₃)	the 3° group: (CH₃)₃CI (SN1)	CH₃OH
Alkyl aryl (C₆H₅OCH₃)	the alkyl: CH₃I	C₆H₅OH

• 3° group: the leaving group departs first and leaves a stable 3° carbocation, so the reaction goes SN1.
• Anisole: O–CH₃ is weaker than O–C₆H₅ (sp² carbon, partial double bond). I⁻ breaks O–CH₃. Phenol goes no further: its sp² carbon can't undergo the substitution needed.

Example (2024) · Cyclohexyl tert-butyl ether + HI → cyclohexanol + (CH₃)₃CI (SN1 at the 3° side).

Example (2026) · C₆H₅–O–CH₂–C₆H₅ + HI → phenol + benzyl iodide, by cleaving the O–CH₂ bond. "Benzyl alcohol + iodobenzene" is false.

Example (2026) · A mixed ether gives two alkyl iodides whose alcohols (after aq. NaOH) both give yellow iodoform. CH₃CH₂–O–CH(CH₃)CH₂CH₃: ethanol and butan-2-ol both carry CH₃CH(OH)–.

Example (2019, 2024) · Excess HBr on an anisole that also has a C=C cleaves the ether to the phenol and adds HBr to the alkene (Markovnikov, Br on the benzylic carbon). CH₃O–C₆H₄–CH=CH–CH₃ → HO–C₆H₄–CHBr–CH₂CH₃.

Electrophilic substitution of aryl ethers: –OR activates the ring and directs o, p, as –OH does in phenol.

Reaction	Reagent	Product
Bromination	Br₂ in ethanoic acid, no FeBr₃	p-bromoanisole (90%) + o
FC alkylation	CH₃Cl, anhyd. AlCl₃	2- and 4-methylanisole
FC acylation	CH₃COCl, anhyd. AlCl₃	2- and 4-methoxyacetophenone (p major)
Nitration	conc. H₂SO₄ + conc. HNO₃	o- and p-nitroanisole

Epoxides · Beyond NCERT · Three-membered cyclic ethers (oxiranes) open far more easily than open-chain ethers because of ring strain; excess HBr breaks both C–O bonds (2020).

10 · Named reactions and reagents

Name	Reagents	Product
Hydroboration–oxidation	(i) B₂H₆ (ii) H₂O₂, OH⁻	anti-Markovnikov alcohol
Acid hydration	H₂O, H⁺	Markovnikov alcohol
Grignard synthesis	RMgX + C=O, then H₃O⁺	1°, 2°, 3° alcohol
Lucas test	conc. HCl + ZnCl₂	R–Cl turbidity: 3° at once
PCC oxidation	pyridinium chlorochromate	1° → aldehyde
Dehydrogenation	Cu, 573 K	aldehyde, ketone; 3° → alkene
Williamson	RO⁻Na⁺ + 1° R′X	R–O–R′
Ether cleavage	conc. HI, heat	R–I + R′–OH
Fermentation	invertase, then zymase (yeast)	C₂H₅OH + CO₂
Methanol synthesis	CO + 2H₂, ZnO–Cr₂O₃	CH₃OH
Iodoform · Beyond NCERT	I₂, NaOH	CHI₃ from CH₃CH(OH)–

11 · Traps

Trap	What goes wrong	Do this
Hydration vs hydroboration	Putting –OH on the same carbon both times	H⁺/H₂O: Markovnikov; B₂H₆: anti-Markovnikov
Dehydration product	Writing the alkene from the original cation	Shift H or CH₃ to a 3° cation, then Saytzeff
Williamson pair	Using a 3° or 2° halide	Halide 1°; bulky part as the alkoxide
Aryl ether by Williamson	ArX + RO⁻	ArO⁻ + RX
Anisole + HI	Writing iodobenzene + methanol	Phenol + CH₃I; Ar–O never breaks
Mixed ether, 3° group	Putting I on the smaller group	3° side becomes the iodide (SN1)
Alcohol acidity	Ranking alcohols above water	H₂O > CH₃OH > 1° > 2° > 3°
Lucas with 1°	Expecting quick turbidity	1° none at room temperature; ethanol too
Cu, 573 K on 3°	Writing a ketone	3° gives the alkene
Ethanol + H₂SO₄	Mixing up 413 K and 443 K	413 K ether (lower T, excess alcohol); 443 K alkene
Ether b.p.	Putting ethers near alcohols	Ethers ≈ alkanes; alcohols far higher
Acetylation mass	Adding 43 or 60 per –OH	+42 per –OH (H replaced by COCH₃)

12 · Numbers worth knowing

• C–O: 142 pm (methanol), 141 pm (ether), 136 pm (phenol). Angles: C–O–H 108.9°, C–O–C 111.7°.
• b.p.: methanol 337 K, ethanol 351 K, methoxymethane 248 K, propane 231 K; pentane 309.1 K, ethoxyethane 307.6 K, butan-1-ol 390 K.
• Dehydration: ethanol 443 K (ether at 413 K); propan-2-ol 85% H₃PO₄, 440 K; tert-butanol 20% H₃PO₄, 358 K.
• Cu dehydrogenation: 573 K. Fermentation stops at ~14% alcohol.
• Methanol synthesis: 200–300 atm, 573–673 K, ZnO–Cr₂O₃.

13 · For the boards only

JEE Main doesn't ask this, but the CBSE paper can.

• Alcohols, phenols and ethers are the base for detergents, antiseptics and fragrances respectively.
• Ordinary spirit for polishing wooden furniture is chiefly ethanol; sugar, cotton and paper are made of –OH compounds.
• Brown shared the 1979 chemistry Nobel with Wittig for his work on organoboron compounds.
• Ethanol acts on the central nervous system: moderate amounts affect judgment and lower inhibitions; higher amounts cause nausea, loss of consciousness and can stop breathing.
• In wine making, grapes supply both the sugar and the yeast (on the skin); crushing brings them together.
• Diethyl ether was widely used as an inhalation anaesthetic, but its slow action and unpleasant recovery led to its replacement.
• Williamson was born in London of Scottish parents and became professor at University College, London, in 1849.