Identification of Reducing Properties and Glucosidic Linkages in Sugars X and Y

To determine the correct statements about sugars $\mathbf{X}$ and $\mathbf{Y}$, we analyze their structures, the nature of their anomeric carbons, and the stereochemistry of their glycosidic linkages.

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1. Analysis of Sugar $\mathbf{X}$ (Sucrose):

• Structure: Sugar $\mathbf{X}$ is composed of an $\alpha\text{-D}$-glucopyranosyl unit linked to a $\beta\text{-D}$-fructofuranosyl unit.
• Linkage Stereochemistry:
  • At the $\text{C-1}$ anomeric center of the glucose ring, the glycosidic bond is oriented downwards (axial/$\alpha$-configuration relative to the ring with the $-\text{CH}_2\text{OH}$ group at $\text{C-5}$ oriented upwards).
  • Therefore, the glucosidic linkage in $\mathbf{X}$ is an $\alpha$-linkage ($\alpha\text{-D-(1}\to\text{2)}-\beta\text{-D}$ linkage).
• Reducing Nature:
  • The glycosidic bond is formed between the anomeric carbon ($\text{C-1}$) of glucose and the anomeric carbon ($\text{C-2}$) of fructose.
  • Since both anomeric carbons are tied up in the glycosidic bond, there are no free hemiacetal or hemiketal groups capable of opening into a free aldehyde or ketone.
  • Thus, $\mathbf{X}$ is a non-reducing sugar.

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2. Analysis of Sugar $\mathbf{Y}$ (Cellobiose-type Disaccharide):

• Structure: Sugar $\mathbf{Y}$ consists of two pyranose rings linked via a glycosidic bond between $\text{C-1}$ of the left ring and $\text{C-4}$ of the right ring.
• Linkage Stereochemistry:
  • At the $\text{C-1}$ anomeric carbon of the left glucose ring, the glycosidic oxygen is oriented upwards (equatorial/$\beta$-configuration, cis to the $-\text{CH}_2\text{OH}$ group at $\text{C-5}$).
  • Therefore, the glucosidic linkage in $\mathbf{Y}$ is a $\beta$-linkage ($\beta\text{-(1}\to\text{4)}$ linkage).
• Reducing Nature:
  • The right-hand pyranose ring has a free hemiacetal group at its anomeric carbon ($\text{C-1}$ has an $-\text{OH}$ group).
  • This hemiacetal group can undergo mutarotation and open to form a free aldehyde in aqueous solution, which can reduce Fehling's solution or Tollens' reagent.
  • Thus, $\mathbf{Y}$ is a reducing sugar.

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Conclusion:

• Statement (B): $\mathbf{X}$ is a non-reducing sugar and $\mathbf{Y}$ is a reducing sugar. (Correct)
• Statement (C): The glucosidic linkages in $\mathbf{X}$ and $\mathbf{Y}$ are $\alpha$ and $\beta$, respectively. (Correct)

Therefore, the correct options are B and C.