JEE Main PYQ | Cis or Trans? Which Acid Forms Anhydride? 🔥 | Maleic vs Fumaric Acid Heating

Описание: In this video, I provide a clear and conceptual solution for Question 44 from the JEE Main 2021 exam (Paper I, Chemistry), held on 25th July 2021 (Shift 2).

In this video, I provide a clear and conceptual solution for Question 44 from the JEE Main 2021 exam (Paper I, Chemistry), held on 25th July 2021 (Shift 2).

🧪 The Question: "Maleic anhydride can be prepared by:" (1) Heating trans-but-2-enedioic acid (2) Heating cis-but-2-enedioic acid (3) Treating trans-but-2-enedioic acid with alcohol and acid (4) Treating cis-but-2-enedioic acid with alcohol and acid

📝 Solution Breakdown:

Identify the Isomers:

Maleic Acid: The Cis isomer of but-2-enedioic acid. The two carboxylic acid groups (−COOH) are on the same side.

Fumaric Acid: The Trans isomer. The groups are on opposite sides.

Reaction Mechanism (Dehydration):

To form an anhydride (cyclic structure), the two −COOH groups must be close enough to lose a water molecule (H2O).

Cis-isomer (Maleic Acid): The groups are adjacent, so heating it easily eliminates water to form Maleic Anhydride.

Trans-isomer (Fumaric Acid): The groups are far apart (opposite sides). Heating it does not form the anhydride directly; it usually sublimes or requires very high temperatures to first isomerize.

Options 3 & 4: Treating with alcohol and acid is an Esterification reaction, not dehydration to anhydride.

✅ Correct Answer: Option (2) Heating cis-but-2-enedioic acid.

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