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Questions and Answers
Which of the following is the correct classification of D-glucose?
Which of the following is the correct classification of D-glucose?
- Disaccharide, ketose, L-enantiomer
- Monosaccharide, ketose, L-enantiomer
- Disaccharide, aldose, D-enantiomer
- Monosaccharide, aldose, D-enantiomer (correct)
What is the difference between an anomeric carbon and a chiral carbon in a sugar molecule?
What is the difference between an anomeric carbon and a chiral carbon in a sugar molecule?
- Anomeric carbons are always part of a ring, chiral carbons may or may not be
- Chiral carbons determine the stereochemistry, anomeric carbons do not
- Anomeric carbons can form hemiacetals, chiral carbons cannot (correct)
- There is no difference, they are the same thing
Which of the following is the correct naming convention for the $\alpha$-D-glucopyranose structure shown?
Which of the following is the correct naming convention for the $\alpha$-D-glucopyranose structure shown?
- $\beta$-D-Glucose
- $\alpha$-D-Glucose (correct)
- $\alpha$-L-Glucose
- $\beta$-L-Glucose
What is the structural difference between an aldose and a ketose sugar?
What is the structural difference between an aldose and a ketose sugar?
Which of the following statements about epimers is correct?
Which of the following statements about epimers is correct?
What is the structural difference between $\alpha$-D-glucopyranose and $\beta$-D-glucopyranose?
What is the structural difference between $\alpha$-D-glucopyranose and $\beta$-D-glucopyranose?
Which of the following is the correct representation of the chair conformation of $\beta$-D-glucopyranose?
Which of the following is the correct representation of the chair conformation of $\beta$-D-glucopyranose?
What is the relationship between D-glucose and D-fructose?
What is the relationship between D-glucose and D-fructose?
Which of the following is the correct name for the $\beta$-D-fructofuranose structure shown?
Which of the following is the correct name for the $\beta$-D-fructofuranose structure shown?
What is the purpose of the Haworth projection in representing monosaccharide structures?
What is the purpose of the Haworth projection in representing monosaccharide structures?
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Study Notes
D and L Notations
- The letter L is assigned to the structure with the —OH on the left
- The letter D is assigned to the structure with —OH on the right
- The —OH on the chiral atom farthest from the carbonyl group is used to assign the D or L configuration
Monosaccharides
- Also known as simple sugars
- Classified by:
- Number of carbons
- Whether aldoses or ketoses
- Most (99%) are straight-chain compounds
- D-glyceraldehyde is the simplest of the aldoses (aldotriose)
- All other sugars have the ending -ose (glucose, galactose, ribose, lactose, etc…)
Aldose Sugars
- General formula: H(HC=O)â‚™CHâ‚‚OH
- Aldose sugars have a carbonyl group (HC=O)
Ketose Sugars
- General formula: (HC=O)â‚™CHâ‚‚OH
- Ketose sugars have a carbonyl group (HC=O) in a different position
Structure of Sugars
- Fisher projection: straight chain representation
- Haworth projection: simple ring in perspective
- Conformational representation: chair and boat configurations
Haworth Projections
- Draw either a six or 5-membered ring including oxygen as one atom
- Number the ring clockwise starting next to the oxygen
- If the substituent is to the right in the Fisher projection, it will be drawn down in the Haworth projection (Down-Right Rule)
- For D-sugars, the highest numbered carbon (furthest from the carbonyl) is drawn up
- For L-sugars, it is drawn down
- For D-sugars, the OH group at the anomeric position is drawn down for α and up for β
- For L-sugars, α is up and β is down
Cyclic Hemiacetals
- Can form either furanose or pyranose structures
- Five-membered rings are close to being planar
- Haworth projections are adequate to represent furanoses
- Six-membered rings are more accurately represented as a chair conformation
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