JEE (Advanced) 2026, Paper 1, Chemistry, Section 3 — the answer is a numerical value: +4 if only the correct value is entered, 0 in all other cases.
Q.11 The sum of total number of carbonyl groups ( >C=O ) present in the major products X and Y in the following reactions is ____.
Two flasks, watched at two levels at once — the flask on the left, the atoms on the right, in step. Press START EXPERIMENT: load → decarboxylation → keto–enol → decarboxylation → keto–enol (X) → nucleophilic attack → proton transfer → water leaves (Y) → audit → answer.
Two flasks, two diacids, one question: how many C=O survive the heat? The question's reactions are loaded — press START EXPERIMENT.
Pink curved arrows move one electron pair each. Red dashes are bonds breaking, green are bonds forming. Charges are worked out from the bonds.
counted from the bonds after every mechanistic step
falls by 44 for each CO₂ and by 18 for the water
not yet examined
not yet examined
not yet examined
not yet examined
Nothing investigated yet.
Step through either mechanism at your own pace. Drag the slider through a step to watch the arrows appear, the old bonds fade and the new ones form; read which bonds broke, which formed, and how many C=O the molecule has at that moment.
Run the experiment — the solution opens with the answer.
The experiment has not finished yet. Press START and let it run to the end — or use Reveal anyway in the header if you are revising.
A ketone, an aldehyde, an acid, an ester and an anhydride all contain >C=O. Each reactant starts with 3.
A CO₂H on the carbon next to a C=O leaves as CO₂ on heating, through a six-membered cyclic transition state, giving an enol.
Two CO₂H on neighbouring carbons, on the same face, close a five-membered cyclic anhydride on heating.
X keeps only its ketone; Y keeps its ketone and gains two anhydride C=O from the two acids.
Three curved arrows around a six-membered ring: the O–H electrons form the second C=O of CO₂, the C–CO₂H bond becomes the C=C of an enol, the ketone π pair picks up the H. The enol then tautomerises (H⁺ on carbon, H⁺ off oxygen) back to a ketone — which is again next to a CO₂H, so it happens a second time.
Its CO₂H groups hang on C3 and C4, two bonds away from the ketone carbon — no cyclic transition state for CO₂ loss. But the two acids sit side by side on the same face (the wedged ring bonds), so one OH oxygen attacks the other C=O carbon, a proton moves, and water leaves: a five-membered cyclic anhydride.
The water that leaves is made from an OH oxygen and two H — no C=O is lost. CO₂ is a gas that leaves the flask: it is not part of X.
Stopping X after one decarboxylation gives 2 (sum 5); counting the two CO₂ as part of X gives 8; letting Y lose CO₂ too, or letting the water "take a C=O", both undercount. A trans diacid could not close the ring — though, still holding three C=O, the sum would be 4 anyway.
For a student opening it for the first time. The whole investigation runs by itself after one press.
Two diacids are heated. Count the C=O groups in the products X and Y and add them.
The question's reactions are loaded — the dimethyl keto diacid, the cis cyclic diacid, heat. You do not need to change anything.
Try the acid without methyl groups, a γ-keto acid, the trans diacid or no heat. The lab says honestly when a change takes you off the question. ↺ RESTORE QUESTION CONDITIONS puts everything back.
Press ▶ START EXPERIMENT. There is nothing else to click (about a minute; SLOW MOTION or 2× changes the pace).
Left: the flask heats, CO₂ bubbles through limewater or water condenses on the copper sulfate. Right, at the same moment: the curved arrows, the bonds breaking and forming, the intermediates and their charges.
When the audit is complete the lab says ✓ EXPERIMENT COMPLETE and reveals the sum. Badges unlock on the way.
In the Mechanism explorer step through either reaction and drag through each step. Then read the Detailed solution.
Press ▶ REPLAY EXPERIMENT, or change a condition and press ⚙ RUN WITH CUSTOM VALUES. CLASSROOM MODE enlarges everything for a projector.
| Exam | JEE Advanced 2026, Paper 1, Chemistry, Section 3, Q.11 |
|---|---|
| Chapter | Aldehydes, Ketones and Carboxylic Acids |
| Topic | Carboxylic acids on heating - decarboxylation of beta-keto acids and cyclic anhydrides from cis-1,2-diacids |
| Difficulty | Easy-Moderate |
| Answer | — run the experiment |