12th grade chemistry organic explainer video target for NEET 2026 in indian medical entrance exam---Question Stem: 9. Which one of the following will most readily be dehydrated in acidic condition? Options: a) [Chemical structure: A four-carbon chain. The second carbon from the left has a double bond to oxygen (a ketone group). The third carbon from the left has a bond to an OH group.] b) [Chemical structure: A four-carbon chain. The second carbon from the left has a bond to an OH group.] c) [Chemical structure: A five-carbon chain. The second carbon from the left has a double bond to oxygen (a ketone group). The fourth carbon from the left has a bond to an OH group.] d) [Chemical structure: A six-carbon chain. The second carbon from the left has a double bond to oxygen (a ketone group). The fifth carbon from the left has a bond to an OH group.]

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Welcome to this NEET 2026 organic chemistry problem. We need to determine which compound will most readily undergo dehydration in acidic conditions. Let's examine each option carefully. Option A is a beta-hydroxy ketone, option B is a secondary alcohol, option C is a gamma-hydroxy ketone, and option D is a delta-hydroxy ketone. The key is understanding which structure favors dehydration. Let's analyze option A in detail. This is 3-hydroxybutan-2-one, a beta-hydroxy ketone. The structure has four carbons with a ketone group on carbon 2 and a hydroxyl group on carbon 3. The hydroxyl group is in the beta position relative to the carbonyl carbon. This structural arrangement is crucial because beta-hydroxy ketones are known to undergo very facile dehydration reactions in acidic conditions. Now let's examine the dehydration mechanism. In acidic conditions, the hydroxyl group gets protonated first, making it a better leaving group. Water then leaves, forming a carbocation intermediate. Finally, a proton is removed to form the double bond. The key advantage of the beta-hydroxy ketone is that it forms an alpha-beta unsaturated ketone product. This conjugated system is extremely stable due to resonance between the carbonyl group and the double bond, making this dehydration thermodynamically very favorable. Let's compare the other options. Option B is butan-2-ol, a simple secondary alcohol that forms regular alkenes without any conjugation benefits. Option C is a gamma-hydroxy ketone which can form an alpha-beta unsaturated ketone, but the gamma position makes dehydration less favorable than the beta position. Option D is a delta-hydroxy ketone that would form a beta-gamma unsaturated ketone, which lacks the stabilizing conjugation of an alpha-beta system. Therefore, option A with its beta-hydroxy ketone structure remains the most readily dehydrated. In conclusion, the correct answer is option A, 3-hydroxybutan-2-one. This beta-hydroxy ketone will most readily undergo dehydration in acidic conditions because it forms a highly stable alpha-beta unsaturated ketone product. The conjugated system provides significant thermodynamic driving force for the reaction. Remember this key concept for NEET: beta-hydroxy carbonyl compounds undergo facile elimination reactions to form conjugated products. This is an important pattern in organic chemistry that appears frequently in competitive exams.