Read the passage carefully and answer the Questions.
Ethers with the general formula \( C_nH_{2n+2}O \) and functional group C-O-C may be divided as symmetrical and unsymmetrical. Lower symmetrical ether may be obtained by the dehydration of alcohols at low temperatures in the presence of protic acids, such as \( H_2SO_4 \) and \( H_3PO_4 \) whereas at high temperature intramolecular dehydration takes place. Formation of ether from primary alcohols is also accompanied by the formation of small amount of alkenes. Due to the steric hindrance, secondary and tertiary alcohols undergo elimination reaction rather than substitution reaction yielding alkene as major product. Ethers can also be obtained by heating alkyl halides with sodium or potassium alkoxides. Substituted Ethers (secondary & tertiary) can also be prepared using this method. If primary halides are replaced with secondary and tertiary halides, alkenes are the major products.
The major product in the following reaction is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → C (propene)
Alcohols lose water when heated with concentrated sulphuric acid, and the product can be an ether or an alkene. A primary alcohol at about 413 K gives mainly an ether, because one alcohol molecule attacks a protonated one in an \(S_N2\) step. A secondary or tertiary alcohol is too hindered for this attack; it loses water to form a carbocation, which then loses a proton, so elimination gives an alkene as the major product.
Propan-2-ol is a secondary alcohol. The acid protonates the –OH group, water leaves to give the secondary carbocation \( \ce{(CH3)2CH+} \), and loss of a proton from a methyl group gives propene:
\( \displaystyle \ce{CH3-CH(OH)-CH3} \xrightarrow[\text{140}\,^\circ\text{C}]{\text{conc. }\ce{H2SO4}} \ce{CH3-CH=CH2 + H2O} \)
So the major product is propene, structure C.
Why the other options are incorrect
Option (1) A — Incorrect. Diisopropyl ether would need one secondary alcohol molecule to attack another, which steric hindrance prevents; elimination wins.
Option (2) B — Incorrect. Diethyl ether has two-carbon groups and comes from ethanol; propan-2-ol cannot give it, because dehydration does not change the carbon skeleton.
Option (4) D — Incorrect. This ether has tertiary carbon atoms that propan-2-ol does not have, so it cannot form from it.
NCERT (2026-27 edition):
Preparation of Ethers – …
