Given below are two statements: Statement I: Fructose does not contain an aldehydic group but still reduces Tollen’s reagent. Statement II: In the presence of base, fructose undergoes rearrangement to give glucose.
In the light of the above statements, choose the correct answer from the options given below.
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Fructose is a ketose, but it has the ability to reduce Tollen's reagent due to the equilibrium with its aldose form. Always remember that sugar rearrangements can convert between different types of sugars, like ketoses to aldoses.
To solve the given question, we need to analyze both statements separately and determine their validity based on our knowledge of chemistry.
Statement I: Fructose does not contain an aldehydic group but still reduces Tollen’s reagent.
Explanation: Fructose is a ketohexose, meaning it contains a ketone group (rather than an aldehyde group). The Tollen's reagent test is traditionally used to identify aldehydes, which can reduce it to metallic silver. However, fructose is known to reduce Tollen's reagent even though it lacks an aldehyde group. This occurs because, in a basic solution (like that in the Tollen's test), fructose can isomerize (via an enediol rearrangement) to glucose and mannose, both of which contain aldehyde groups and can reduce the Tollen's reagent. Hence, fructose indirectly participates in the reduction.
Therefore, Statement I is true.
Statement II: In the presence of base, fructose undergoes rearrangement to give glucose.
Explanation: In basic conditions, fructose can undergo an isomerization process known as the Lobry de Bruyn–Van Ekenstein transformation. This process allows fructose to convert into glucose and mannose through enediol intermediates. This transformation supports the idea that although fructose initially doesn't have an aldehyde group, it rearranges into glucose, which has an aldehyde group.
Thus, Statement II is true.
Both statements are supported by known chemical processes, which confirms that both statements are indeed true.
Conclusion: Therefore, the correct answer is that Both Statement I and Statement II are true.
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Fructose is a ketohexose, meaning it contains a ketonic group, not an aldehydic group. However, in the presence of an alkaline medium, fructose can isomerize to form glucose and mannose via an enediol intermediate. This is known as the Lobry de Bruyn–Van Ekenstein transformation. Since glucose is an aldose sugar, it contains an aldehydic group that can reduce Tollen’s reagent (ammoniacal silver nitrate), resulting in the reduction of Tollen’s reagent. This explains Statement I, which is true because fructose does not directly contain an aldehydic group but can indirectly cause the reduction.
Statement II is also true because the isomerization of fructose in a basic medium as described above is well-established.
Therefore, the correct answer is: Both Statement I and Statement II are true.
