JEE Main 2026 — Apr 5, Shift 1 — Chemistry solution

JEE Main2026Apr 5, Shift 1Chemistry

Consider compounds A, B and C with the following structural formulae:

A = $CH_{3} CH_{2} CH_{2} CH_{2} CH_{2} OH$ (pentan-1-ol)

B = $CH_{2} = CH CH_{2} CH_{2} CH_{3}$ (pent-1-ene)

C = $HOCH_{2} CH_{2} CH(OH)CH_{3}$ (butane-1,3-diol)

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 ______

Solution

Conversion of pentan-1-ol to pent-1-ene is an acid-catalysed dehydration. PCC oxidises, it does not dehydrate, so (D) is concentrated H $_{2}$ SO $_{4}$ (or H $_{3}$ PO $_{4}$ ).

Butane-1,3-diol, on heating with excess concentrated acid, loses two molecules of water to give a conjugated diene. The two hydroxyls are on C1 and C3, so both eliminations together yield 1,3-butadiene: $CH_{2} = CH CH = CH_{2}$ .

Hence D is conc. H $_{2}$ SO $_{4}$ (or H $_{3}$ PO $_{4}$ ) and E is 1,3-butadiene.

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