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Among the various structural forms in which glucose can exist, which isomer is the most stable?

1. Open-chain aldehydic form
2. Cyclic alpha-pyranose form
3. Open-chain keto form
4. Cyclic beta-pyranose form

Correct answer: Cyclic alpha-pyranose form

Solution

Glucose strongly prefers the cyclic pyranose hemiacetal forms over the open-chain aldehydic or keto forms due to ring stabilisation. Of the four options provided, the cyclic alpha-pyranose form is far more stable than either open-chain form listed, making it the best answer here.

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