Carbohydrates

The term hexose refers to the presence of six carbon atoms and term keto shows the presence of ketonic group. Thus, the compound which contains atoms and one

group is called ketohexose. Among the given only glucose and fructose are six compounds. Out of them, glucose contains an aldehyde group while fructose contains a ketonic group. Hence, the example of ketohexose is

Fructose undergoes enolisation to form an intermediate enolate ion, which then undergoes oxidation to form an aldehyde. This aldehyde group reduces Tollen's reagent.

Step 2: Conclusion.
The correct answer is the enolisation of fructose followed by its conversion to an aldehyde, corresponding to option (d).

In aqueous medium, fructose is enolised and converted into aldehyde in basic medium. Generally all aldehydes reduce Tollen's reagent, thus fructose can also reduces Tollen's reagent.

Step 1: Understanding hemiacetal formation.
When a monosaccharide forms a cyclic hemiacetal, the carbon atom that was part of the carbonyl group becomes the anomeric carbon. This carbon can assume either an - or -anomeric form.

Step 2: Conclusion.
The correct identification is that the anomeric carbon can assume either an - or -position, corresponding to option (4).

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