Carbohydrates Knowledge-Based Download PDF

Questions

1. 1.

   Which of the following reagents selectively oxidizes D-glucose to an aldonic acid while leaving D-fructose unoxidized under neutral or slightly acidic conditions?

   • A) Fehling's solution
   • B) Bromine water ($\text{Br}_2/\text{H}_2\text{O}$)
   • C) Tollens' reagent
   • D) Benedict's solution
2. 2.

   Which statement correctly describes the structural relationship between D-glucose and D-galactose?

   • A) They are enantiomers that have opposite configurations at all chiral centers.
   • B) They are diastereomers that differ in stereochemical configuration exclusively at carbon-4.
   • C) They are constitutional isomers differing in the position of their carbonyl functional groups.
   • D) They are anomers that differ only in the configuration of the hemiacetal carbon.
3. 3.

   Which statement correctly describes the stereochemical relationship between $\alpha$-D-glucopyranose and $\beta$-D-glucopyranose?

   • A) They are enantiomers that represent non-superimposable mirror images of each other at all chiral centers.
   • B) They are constitutional isomers that differ in the sequence of atomic connectivity along the carbon backbone.
   • C) They are geometric isomers that differ due to restricted rotation about a rigid carbon-carbon double bond.
   • D) They are diastereomeric epimers, termed anomers, that differ in configuration specifically at the hemiacetal carbon (C-1).
4. 4.

   Which of the following statements correctly identifies the primary difference in the glycosidic linkages between amylose and cellulose?

   • A) Amylose contains $\beta$-1,4-glycosidic bonds that form rigid linear fibrils, whereas cellulose contains $\alpha$-1,6-glycosidic bonds that form helical coils.
   • B) Amylose contains $\alpha$-1,2-glycosidic bonds between glucose and fructose units, whereas cellulose contains $\beta$-1,4-glycosidic bonds between glucose units.
   • C) Amylose consists of D-glucose units linked by $\beta$-1,4-glycosidic bonds, whereas cellulose consists of D-glucose units linked by $\alpha$-1,4-glycosidic bonds.
   • D) Amylose consists of D-glucose units linked by $\alpha$-1,4-glycosidic bonds, whereas cellulose consists of D-glucose units linked by $\beta$-1,4-glycosidic bonds.
5. 5.

   Which of the following statements correctly explains why sucrose is classified as a non-reducing disaccharide, whereas maltose is a reducing disaccharide?

   • A) Maltose possesses an $\alpha$-(1$\rightarrow$2) glycosidic linkage that locks both rings, whereas sucrose possesses a free aldehyde group at C-1.
   • B) Both anomeric carbons in sucrose are directly involved in the glycosidic bond, leaving no free hemiacetal group capable of opening into an oxidizable aldehyde.
   • C) Sucrose is composed entirely of ketose monomers, which are chemically inert and cannot reduce Benedict's or Tollens' reagents.
   • D) Maltose forms an internal ester linkage upon oxidation, whereas sucrose is completely insoluble in alkaline testing solutions.