JEE Mains Chemistry · Alcohols, Phenols and Ethers

Classification, Preparation and Physical Properties

An alcohol is primary, secondary or tertiary by the number of carbons on the carbinol carbon; it is made by hydration, hydroboration, reduction or a Grignard reagent, and hydrogen bonding gives it a far higher boiling point than an ether or alkane of similar mass.

All Alcohols, Phenols and Ethers notes JEE Mains Chemistry strategy

Why this matters

Thirteen PYQs, twelve of them multiple choice, and three from 2026. Five ask which route makes an alcohol, from Grignard reagents and hydroboration to the controlled oxidation of alkanes and fermentation, and which routes never do. Eight test the class of an alcohol, the common names of phenols, boiling points, solubility in water and the hydrogen bond in o-nitrophenol.

Concept 1 of 2: Routes that make alcohols, and routes that do not

An alcohol forms when an OH ends up on an sp³ carbon. Water can add across a C=C, hydride can add to a C=O, or a Grignard carbon can add to a C=O. Routes that break C=C bonds (ozonolysis) or add water to a C≡C (it tautomerises to a ketone) give carbonyl compounds instead.

Definition

Acid hydration follows Markovnikov's rule through a carbocation, so the carbon skeleton can rearrange.
Hydroboration–oxidation gives the anti-Markovnikov alcohol with no carbocation and no rearrangement.
Reduction: aldehydes give 1° alcohols and ketones give 2° alcohols ( $\mathrm{H_2/Pd}$ , $\mathrm{NaBH_4}$ , $\mathrm{LiAlH_4}$ ). Acids need $\mathrm{LiAlH_4}$ or $\mathrm{B_2H_6}$ ; $\mathrm{NaBH_4}$ does not reduce them.
Grignard reagent + carbonyl, then $\mathrm{H_3O^+}$ : HCHO gives a 1°, any other aldehyde a 2°, a ketone a 3° alcohol.
Controlled oxidation of alkanes: $\mathrm{2CH_4 + O_2}$ over Cu at 523 K and 100 atm gives $\mathrm{CH_3OH}$ ; $\mathrm{(CH_3)_3CH}$ with $\mathrm{KMnO_4}$ gives $\mathrm{(CH_3)_3COH}$ .

Route	Reagents	Product	Watch for
Acid hydration of an alkene	Dilute $\mathrm{H_2SO_4}$ (water, $\mathrm{H^+}$ )	Markovnikov alcohol: $\mathrm{CH_3CH{=}CH_2 \to CH_3CH(OH)CH_3}$	Goes through a carbocation, so methyl and hydride shifts can occur
Hydroboration–oxidation	$\mathrm{B_2H_6}$ , then $\mathrm{H_2O_2/OH^-}$	Anti-Markovnikov alcohol: $\mathrm{CH_3CH{=}CH_2 \to CH_3CH_2CH_2OH}$	No carbocation, so no rearrangement
Reduction of aldehydes and ketones	$\mathrm{H_2/Pd}$ , $\mathrm{NaBH_4}$ or $\mathrm{LiAlH_4}$	Aldehyde → 1° alcohol; ketone → 2° alcohol	Hydrogen adds across the C=O
Reduction of acids and esters	$\mathrm{LiAlH_4}$ or $\mathrm{B_2H_6}$ for acids; esters also by $\mathrm{H_2}$ over a catalyst	Primary alcohol $\mathrm{RCH_2OH}$	$\mathrm{NaBH_4}$ leaves a COOH group alone
Grignard reagent + carbonyl	RMgX in dry ether, then $\mathrm{H_3O^+}$	HCHO → 1°; RCHO → 2°; $\mathrm{R_2CO}$ → 3°	The new C–C bond forms at the old carbonyl carbon
Hydrolysis of an alkyl halide	Aqueous NaOH or KOH	Alcohol with the OH where the halogen was	Aryl halides do not react under these conditions
Controlled oxidation of alkanes	$\mathrm{2CH_4 + O_2}$ , Cu, 523 K, 100 atm; $\mathrm{(CH_3)_3CH + KMnO_4}$	$\mathrm{CH_3OH}$ ; $\mathrm{(CH_3)_3COH}$	With $\mathrm{Mo_2O_3}$ methane gives HCHO; with $\mathrm{(CH_3COO)_2Mn}$ alkanes give acids
Methanol from water gas	$\mathrm{CO + 2H_2}$ , $\mathrm{ZnO{-}Cr_2O_3}$ , 573–673 K, 200–300 atm	$\mathrm{CH_3OH}$	The industrial route to methanol
Fermentation	Sugar with yeast (invertase, then zymase)	Ethanol and $\mathrm{CO_2}$	Air must be kept out, or ethanol is oxidised to ethanoic acid
Ozonolysis of an alkene	$\mathrm{O_3}$ , then Zn and water	Aldehydes and ketones	Never an alcohol: the C=C is cut in two
Hydration of an alkyne	Water with $\mathrm{HgSO_4/H_2SO_4}$	A ketone; ethyne alone gives the aldehyde ethanal	The enol formed first tautomerises; no alcohol survives

Match the product class to the carbonyl: HCHO, other aldehydes and ketones give 1°, 2° and 3° alcohols with a Grignard reagent.

Practice this conceptself-check · 4 quick reps

The same idea in a real exam question:

JEE Mains · 2023 · 10 April 2023 · Q121Moderate

Example 1 · Alcohols, Phenols and Ethers · Classification, Preparation and Physical Properties

Incorrect method of preparation for alcohols from the following is:

Acid hydration can move a methyl group

3,3-Dimethylbut-1-ene with dilute acid gives 2,3-dimethylbutan-2-ol, not 3,3-dimethylbutan-2-ol: the secondary cation takes a 1,2-methyl shift first. Hydroboration of the same alkene gives 3,3-dimethylbutan-1-ol, with no shift.

NaBH₄ does not reduce a carboxylic acid

An acid or ester needs

\mathrm{LiAlH_4}

(or

\mathrm{B_2H_6}

for an acid).

\mathrm{NaBH_4}

reduces only aldehydes and ketones.

Drill 4 more on routes that make alcohols, and routes that do not

Concept 2 of 2: Classes, common names and boiling points

An alcohol's O–H hydrogen-bonds to the O of its neighbour, so its molecules stick together far more than those of an ether, aldehyde or alkane of the same size. Boiling point follows that stickiness. Water can hydrogen-bond to the same O, so small alcohols and ethers dissolve; a longer carbon chain drags solubility down.

Definition

1°, 2°, 3°: count the carbons bonded to the carbinol carbon (ring carbons count). Cyclohexanol is 2°; 1-methylcyclohexan-1-ol is 3°.
Common names: benzene-1,2-diol is catechol, benzene-1,3-diol is resorcinol, benzene-1,4-diol is quinol (hydroquinone); the methylphenols are the cresols.
At similar molar mass the boiling point rises: alkane < ether < aldehyde or ketone < alcohol.
Within a series the boiling point rises with the number of carbons and falls with branching.
Ethoxyethane and butan-1-ol dissolve in water to a similar extent (about 7.5 and 9 g per 100 mL); solubility falls as the alkyl part grows.
Sodium reacts with an alcohol (it gives $\mathrm{H_2}$ ) but not with an ether, so sodium can dry ether but not ethanol.
o-Nitrophenol has an intramolecular hydrogen bond: lower melting and boiling point than p-nitrophenol, and it is steam volatile.

Boiling point at similar molar mass

\text{alkane} < \text{ether} < \text{aldehyde, ketone} < \text{alcohol} < \text{carboxylic acid}

Worked example

Arrange propane, methoxymethane, ethanal and ethanol in increasing order of boiling point. Their molar masses are close (44 to 46 g mol

^{-1}

Practice this conceptself-check · 4 quick reps

The same idea in a real exam question:

JEE Mains · 2023 · 8 Apr 2023 · Q42Moderate

Example 2 · Alcohols, Phenols and Ethers · Classification, Preparation and Physical Properties

Given below are two statements: One is labelled as Assertion

A

and the other is labelled as Reason R. Assertion A: Butan -1- ol has higher boiling point than ethoxyethane. Reason R: Extensive hydrogen bonding leads to stronger association of molecules. In the light of the above statements, choose the correct answer from the options given below:

Isomers can differ by 80 K

Butan-1-ol (391 K) and ethoxyethane (308 K) have the same formula,

\mathrm{C_4H_{10}O}

. The gap comes only from hydrogen bonding between alcohol molecules.

Ring carbons count as carbon neighbours

A ring OH on a CH is secondary; a ring OH on a carbon that also carries a methyl group is tertiary. Count every carbon bonded to the carbinol carbon, inside the ring or outside it.

The chelated isomer melts lower

o-Nitrophenol (about 45 °C) melts far below p-nitrophenol (about 114 °C). Its hydrogen bond is inside one molecule, so it does not hold molecules together.

Drill 7 more on classes, common names and boiling points

Summary — formulas & gotchas at a glance

A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.

Formulas (1)

Classes, common names and boiling points
Boiling point at similar molar mass
$\text{alkane} < \text{ether} < \text{aldehyde, ketone} < \text{alcohol} < \text{carboxylic acid}$

Reference tables (1)

Routes that make alcohols, and routes that do not11 rows

Route	Reagents	Product	Watch for
Acid hydration of an alkene	Dilute $\mathrm{H_2SO_4}$ (water, $\mathrm{H^+}$ )	Markovnikov alcohol: $\mathrm{CH_3CH{=}CH_2 \to CH_3CH(OH)CH_3}$	Goes through a carbocation, so methyl and hydride shifts can occur
Hydroboration–oxidation	$\mathrm{B_2H_6}$ , then $\mathrm{H_2O_2/OH^-}$	Anti-Markovnikov alcohol: $\mathrm{CH_3CH{=}CH_2 \to CH_3CH_2CH_2OH}$	No carbocation, so no rearrangement
Reduction of aldehydes and ketones	$\mathrm{H_2/Pd}$ , $\mathrm{NaBH_4}$ or $\mathrm{LiAlH_4}$	Aldehyde → 1° alcohol; ketone → 2° alcohol	Hydrogen adds across the C=O
Reduction of acids and esters	$\mathrm{LiAlH_4}$ or $\mathrm{B_2H_6}$ for acids; esters also by $\mathrm{H_2}$ over a catalyst	Primary alcohol $\mathrm{RCH_2OH}$	$\mathrm{NaBH_4}$ leaves a COOH group alone
Grignard reagent + carbonyl	RMgX in dry ether, then $\mathrm{H_3O^+}$	HCHO → 1°; RCHO → 2°; $\mathrm{R_2CO}$ → 3°	The new C–C bond forms at the old carbonyl carbon
Hydrolysis of an alkyl halide	Aqueous NaOH or KOH	Alcohol with the OH where the halogen was	Aryl halides do not react under these conditions
Controlled oxidation of alkanes	$\mathrm{2CH_4 + O_2}$ , Cu, 523 K, 100 atm; $\mathrm{(CH_3)_3CH + KMnO_4}$	$\mathrm{CH_3OH}$ ; $\mathrm{(CH_3)_3COH}$	With $\mathrm{Mo_2O_3}$ methane gives HCHO; with $\mathrm{(CH_3COO)_2Mn}$ alkanes give acids
Methanol from water gas	$\mathrm{CO + 2H_2}$ , $\mathrm{ZnO{-}Cr_2O_3}$ , 573–673 K, 200–300 atm	$\mathrm{CH_3OH}$	The industrial route to methanol
Fermentation	Sugar with yeast (invertase, then zymase)	Ethanol and $\mathrm{CO_2}$	Air must be kept out, or ethanol is oxidised to ethanoic acid
Ozonolysis of an alkene	$\mathrm{O_3}$ , then Zn and water	Aldehydes and ketones	Never an alcohol: the C=C is cut in two
Hydration of an alkyne	Water with $\mathrm{HgSO_4/H_2SO_4}$	A ketone; ethyne alone gives the aldehyde ethanal	The enol formed first tautomerises; no alcohol survives

Match the product class to the carbonyl: HCHO, other aldehydes and ketones give 1°, 2° and 3° alcohols with a Grignard reagent.

Watch out for (5)

Acid hydration can move a methyl group
→ Routes that make alcohols, and routes that do not
NaBH₄ does not reduce a carboxylic acid
→ Routes that make alcohols, and routes that do not
Isomers can differ by 80 K
→ Classes, common names and boiling points
Ring carbons count as carbon neighbours
→ Classes, common names and boiling points
The chelated isomer melts lower
→ Classes, common names and boiling points

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