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For the open-chain aldehyde form of D-glucose (CHO at top; followed by H-C-OH, HO-C-H, H-C-OH, H-C-OH, CH2OH), which of the following statements is INCORRECT?

1. It can be oxidised to a dicarboxylic acid using bromine water
2. Despite having a -CHO group, it does not give a positive Schiff test
3. It has 4 asymmetric carbon atoms
4. It exists in equilibrium with 2 other cyclic structures in solution

Correct answer: It can be oxidised to a dicarboxylic acid using bromine water

Solution

Bromine water is selective: it oxidises only the aldehyde (-CHO) to a carboxylic acid (-COOH), producing gluconic acid (a monocarboxylic acid). To obtain a dicarboxylic acid (glucaric acid), both the CHO and CH2OH ends must be oxidised, which requires concentrated HNO3. Therefore, the statement that Br2 water can oxidise glucose to a dicarboxylic acid is INCORRECT. The other statements are correct: glucose gives a positive Schiff test, has 4 stereocentres (C2-C5), and exists as alpha- and beta-pyranose forms in equilibrium with the open chain.

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