24 Questions
What is the difference between aldoses and ketoses in terms of the position of the C=O group?
Aldoses have the C=O group in carbon 1, while ketoses have the C=O group in another carbon that is not C1.
What is the term for isomers that differ in the position of H atoms and double bonds?
Tautomers
What is the term for the conversion of aldoses into ketoses and vice-versa?
Tautomeric shift
What is the difference between D-isomers and epimers?
D-isomers are molecules that have the -OH group on the right side of the highest numbered chiral carbon, while epimers are isomers that differ in the configuration of one carbon.
What is the term for monosaccharides with 5 or more carbons that exist in a ring structure?
Cyclic structure
What are the three most common monosaccharides in the human diet?
Glucose, fructose, and galactose
What is the term for the two cyclic forms of D-glucose?
Alpha-D-glucose and beta-D-glucose
What type of isomers can aldoses and ketoses have?
Epimers
What is the result of the reaction of an alcohol with an aldehyde?
Hemiacetal
What is the term for the interconversion of alpha and beta anomers?
Mutarotation
What type of sugar is capable of acting as a reducing agent?
Reducing sugar
What is the name of the 6-membered ring structure formed in sugars?
Pyranose
What is the difference between Fisher and Haworth projections?
Fisher projection shows the open chain, while Haworth projection shows the closed-cyclic structure
What is the characteristic of an aldose that allows it to act as a reducing sugar?
Free aldehyde group
What is the term for the carbon atom in the carbonyl group of a monosaccharide?
Anomeric carbon
What is the name of the 5-membered ring structure formed in sugars?
Furanose
What are the two main types of monosaccharides based on the location of the C=O group?
Aldoses and ketoses
What is the difference between D-monosaccharides and L-monosaccharides?
The location of the -OH group in the highest numbered asymmetric carbon.
What type of isomers are formed when two monosaccharides differ in the configuration of one carbon?
Epimers
What is the minimum number of carbon atoms required for a sugar to be a monosaccharide?
3
What type of projection is used to represent monosaccharides in a linear form?
Fisher projection
What is the term for monosaccharides that contain one or more asymmetric carbon atoms?
Chiral isomers
Which type of sugar is more prevalent in nature?
D-sugars
What is the term for two monosaccharides that are mirror images of each other?
Enantiomers
Study Notes
Monosaccharides
- Monosaccharides are simple sugars with at least 3 carbons, one of which contains a carbonyl group (C=O), and the others contain a hydroxyl group (–OH).
Aldoses and Ketoses
- Aldoses have the C=O group in carbon 1, making them an aldehyde.
- Ketoses have the C=O group in another carbon, making them a ketose.
Nomenclature
- Monosaccharides are named based on the number of carbons: triose (3C), tetrose (4C), pentose (5C), hexose (6C), heptose (7C), etc.
Isomerism in Monosaccharides
- Isomers have the same molecular formula but differ in structure.
- Chiral isomers are mirror images of each other, and all monosaccharides (except di-hydroxyacetone) contain one or more asymmetric carbon atoms, and therefore can have chiral isomers.
- D-monosaccharide: -OH group is on the right side; L-monosaccharide: -OH group is on the left side.
- Epimers: two monosaccharides that differ in the configuration of one carbon.
- Constitutional (or structural) isomers: isomers with different atom arrangement; aldose and ketone with the same number of carbons are constitutional isomers.
- Tautomers: structural isomers that differ in the position of H atoms and double bonds; aldoses can be converted into ketoses and vice-versa.
Anomers and Mutarotation
- Anomers are formed when the carbonyl group (C=O) forms a covalent bond with the oxygen of a hydroxyl group (-OH) along the chain.
- In an aldose, such as D-glucose, carbon 1 becomes a chiral center, forming two isomers: alpha-isomer and beta-isomer.
- Mutarotation is the interconversion of alpha and beta anomers.
Hemiacetal and Hemiketal Formation
- Hemiacetal results from the reaction of an alcohol with an aldehyde.
- Hemiketal results from the reaction of an alcohol with a ketone.
- Formation of a cyclic hemiacetal from aldose forms two anomers: alpha-D-glucose and beta-D-glucose.
- Formation of a cyclic hemiketal from ketone forms two anomers: alpha-D-fructose and beta-D-fructose.
- Pyranose = sugar with a 6-membered ring; Furanose = sugar with a 5-membered ring.
Fisher and Haworth Projections
- Fisher projection shows the open chain of the monosaccharide.
- Haworth projection shows the closed-cyclic structure of the monosaccharide, highlighting the anomeric carbon and anomeric isomers.
Reducing Sugars
- Monosaccharides are reducing sugars, capable of acting as a reducing agent.
- Aldoses in the open (linear) form have a free aldehyde group, which reacts with oxidizing agents to reduce them.
- Ketoses can also be reducing sugars, if the ketone group shifts to be an aldose before oxidation.
Learn about the formation of isomers around carbon 1 in aldoses, such as D-glucose, and how the position of the hydroxyl group determines the alpha or beta isomer. Understand the concept of anomeric carbon in carbonyl groups.
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