Chemistry Q67 – JEE-MAIN 2026

Home Chemistry Basic Organic ChemistryQuestion #116

Consider compounds A, B and C with following structural formulae A = CH

_{3}

– CH

_{2}

– CH

_{2}

– CH

_{2}

– CH

_{2}

– OH B = CH

_{2}

= CH – CH

_{2}

– CH

_{2}

– CH

_{3}

C = HO – CH

_{2}

– CH

_{2}

– CH(OH) – CH

_{3}

For the conversion of B from A. reagent (D) required is _______ and structural formula of product (E) obtained when C undergoes same reaction using excess reagent (D) is _______.

Clue 1 of 3: Reaction Type Identification

The conversion of an alcohol to an alkene is a dehydration reaction.

🧠 Full Solution Path

Step 1: Identify Reagent (D) for A to B conversion✦ Active

Compound A is Pentan-1-ol (CH $_{3}$ – CH $_{2}$ – CH $_{2}$ – CH $_{2}$ – CH $_{2}$ – OH), and compound B is Pent-1-ene (CH $_{2}$ = CH – CH $_{2}$ – CH $_{2}$ – CH $_{3}$ ). The conversion of an alcohol to an alkene is a dehydration reaction. Strong acid catalysts like concentrated sulfuric acid ( $H_{2} S O_{4}$ ) or phosphoric acid ( $H_{3} P O_{4}$ ) are used for this purpose. PCC (Pyridinium Chlorochromate) is an oxidizing agent, not a dehydrating agent. Therefore, reagent (D) must be Conc. H $_{2}$ SO $_{4}$ or H $_{3}$ PO $_{4}$ . This eliminates options 2 and 3.

Step 2: Determine Product (E) from C with excess Reagent (D)○ Expand

Compound C is Butane-1,3-diol (HO – CH $_{2}$ – CH $_{2}$ – CH(OH) – CH $_{3}$ ). When C undergoes the same reaction (dehydration) with excess reagent (D) (Conc. H $_{2}$ SO $_{4}$ or H $_{3}$ PO $_{4}$ ), both hydroxyl groups will be dehydrated.

HO - {CH}_{2} - {CH}_{2} - CH(OH) - {CH}_{3} \overset{{Conc. H}_{2} {SO}_{4} (excess)}{\to} {CH}_{2} = CH - CH = {CH}_{2} + 2 H_{2} O

The product (E) formed is Buta-1,3-diene (CH $_{2}$ = CH – CH = CH $_{2}$ ). This involves the removal of two molecules of water. Option 1's product (CH $_{2}$ = CH(OH)CH $_{3}$ ) is an enol with 3 carbons, which is incorrect. Option 2's product (HO – CH $_{2}$ – CH $_{2}$ – CH = CH $_{2}$ ) is a mono-dehydrated product, which is not expected with 'excess' reagent.

💡 Teacher's Secret Hint

Remember that 'excess' dehydrating agent implies complete dehydration of all possible hydroxyl groups.

Step 3: Match with Options○ Expand

Based on the identification of reagent (D) as Conc. H $_{2}$ SO $_{4}$ or H $_{3}$ PO $_{4}$ and product (E) as CH $_{2}$ = CH – CH = CH $_{2}$ , option 4 is the correct choice.

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Chemistry Question 67 – JEE-MAIN 2026

Clue 1 of 3: Reaction Type Identification

🧠 Full Solution Path