JEE Main 2026 — Alcohols Phenols and Ethers Question with Solution
JEE Main 2026 (04 April Shift 1)
Question
Identify the colour of compound in the sequence of the reaction.
Choose an option
Show full solutionCorrect option: D
Correct answer
DColourless
Step-by-step explanation
The given reaction sequence represents the synthesis and acid-base behaviour of phenolphthalein.
When phenol reacts with phthalic anhydride in the presence of concentrated , phenolphthalein is formed. In acidic or neutral medium, phenolphthalein exists in a lactone form which is colourless.
Upon addition of a moderate amount of alkali (NaOH), the lactone ring opens and a proton is removed, forming a dianion with an extended conjugated quinonoid structure. This extended conjugation is responsible for the characteristic pink colour of phenolphthalein in basic medium.
When excess NaOH is added (strongly alkaline medium), a hydroxide ion attacks the central hybridized carbon atom of the quinonoid structure. This converts the central carbon to an hybridized state, forming a carbinol structure (compound X).
Because the central carbon is now hybridized, the extended conjugation is broken. As a result, the compound loses its colour and becomes colourless.
Therefore, compound X is colourless.
Answer: Colourless
When phenol reacts with phthalic anhydride in the presence of concentrated , phenolphthalein is formed. In acidic or neutral medium, phenolphthalein exists in a lactone form which is colourless.
Upon addition of a moderate amount of alkali (NaOH), the lactone ring opens and a proton is removed, forming a dianion with an extended conjugated quinonoid structure. This extended conjugation is responsible for the characteristic pink colour of phenolphthalein in basic medium.
When excess NaOH is added (strongly alkaline medium), a hydroxide ion attacks the central hybridized carbon atom of the quinonoid structure. This converts the central carbon to an hybridized state, forming a carbinol structure (compound X).
Because the central carbon is now hybridized, the extended conjugation is broken. As a result, the compound loses its colour and becomes colourless.
Therefore, compound X is colourless.
Answer: Colourless
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