Answer
🔍 What is a Hemiacetal?
A hemiacetal is an organic compound formed when an aldehyde reacts with one equivalent of an alcohol under acidic (or sometimes neutral) conditions.
Aldehyde + Alcohol → Hemiacetal
The product contains both an –OH group and an –OR (alkoxy) group on the same carbon atom.
✅ Correct Answer
✔ Hemiacetal is the result of the reaction of an aldehyde with one equivalent of alcohol under acidic conditions.
❌ Incorrect Options Explained
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✘ Formed from esters — esters do not form hemiacetals with alcohols; they undergo transesterification or hydrolysis.
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✘ Formed from amides — amides react differently (usually via hydrolysis); they do not yield hemiacetals.
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✘ Protecting group stable under acidic conditions — hemiacetals are not stable under acidic conditions and are often converted to acetals for protection.
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✘ None of these — Incorrect because one of the statements is valid.
📘 Summary
Hemiacetals are key intermediates in carbohydrate chemistry and are important in organic synthesis. They are typically converted to acetals for stability and protection purposes.