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Questions and Answers
What distinguishes aldoses from ketoses?
What distinguishes aldoses from ketoses?
Which term describes monosaccharides with four carbon atoms?
Which term describes monosaccharides with four carbon atoms?
What is the classification of glucose?
What is the classification of glucose?
Which process forms the ring structure of sugars from an aldehyde group?
Which process forms the ring structure of sugars from an aldehyde group?
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Which of the following represents a hexose?
Which of the following represents a hexose?
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What are aldotrioses?
What are aldotrioses?
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What is the characteristic structure of pyranose?
What is the characteristic structure of pyranose?
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What determines if a sugar is classified as an α-sugar or a β-sugar?
What determines if a sugar is classified as an α-sugar or a β-sugar?
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What term describes the 1-4 ring form that resembles an organic compound called furan?
What term describes the 1-4 ring form that resembles an organic compound called furan?
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What type of carbon atom is known as an asymmetric carbon atom?
What type of carbon atom is known as an asymmetric carbon atom?
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Which statement about optical isomerism is correct?
Which statement about optical isomerism is correct?
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What is the formula to determine the number of isomers for a substance containing asymmetric carbon atoms?
What is the formula to determine the number of isomers for a substance containing asymmetric carbon atoms?
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Which of the following chemically signifies D and L isomers?
Which of the following chemically signifies D and L isomers?
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What is the anomeric carbon in an aldose sugar?
What is the anomeric carbon in an aldose sugar?
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What is mutarotation in the context of optically active substances?
What is mutarotation in the context of optically active substances?
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What is the specific rotation of β-glucose when freshly dissolved in water?
What is the specific rotation of β-glucose when freshly dissolved in water?
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Study Notes
Naming Monosaccharides
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Monosaccharides can be named based on the presence of an aldehyde or ketone group
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Aldoses: Monosaccharides containing an aldehyde group (-CHO). The suffix "-ose" generally means sugar.
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Ketoses: Monosaccharides containing a ketone group (-C=O).
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Monosaccharides can also be named based on the number of carbon atoms they contain:
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Trioses: 3 carbon atoms
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Tetroses: 4 carbon atoms
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Pentoses: 5 carbon atoms
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Hexoses: 6 carbon atoms
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Heptoses: 7 carbon atoms
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To classify monosaccharides fully, both the presence of the aldehyde or ketone group and the number of carbon atoms are used:
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Aldotrioses and ketotrioses
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Aldotetroses and ketotetroses
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Aldopentoses and ketopentoses
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Aldohexoses and ketohexoses
Classification of Monosaccharides
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Trioses:
- Aldotrioses: Glyceraldehyde (glycerose), the "parent" sugar
- Ketotrioses: Dihydroxyacetone
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Tetroses:
- Aldotetroses: Erythrose
- Ketotetroses: Erythrulose
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Pentoses:
- Aldopentoses: Ribose, arabinose, xylose, and lyxose
- Ketopentoses: Ribulose and xylulose
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Hexoses:
- Aldohexoses: Glucose, galactose, and mannose
- Ketohexoses: Fructose
Ring (Cyclic) Structures of Sugars
- Simple open-chain formulas for sugars don’t explain reactions like the inability of glucose to react fully like an aldehyde. This suggests the aldehyde group is “masked” in some way.
- In solution, sugars with aldehyde groups undergo these transformations:
- Hydration: The aldehyde group is hydrated to form an aldenol group (alcohol).
- Condensation: The -OH of the aldenol group condenses with the -OH on C4 or C5 to form a ring structure (hemiacetal structure).
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α or β form:
- If the remaining -OH is on the right side, it’s an α-sugar.
- If the remaining -OH is on the left side, it’s a β-sugar.
Pyranose and Furanose
- The 1-5 ring form is called pyranose because it resembles pyran (e.g., α and β glucopyranose).
- The 1-4 ring form is called furanose because it resembles furan (e.g., α and β glucofuranose).
Asymmetric Carbon Atoms
- An asymmetric carbon atom is attached to four different groups or atoms.
- Compounds with asymmetric carbons, known as chiral centers, exhibit two properties:
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Optical Activity: They rotate the plane of polarized light.
- (ɗ) or (+) = dextrorotatory, rotates the plane of polarized light to the right.
- (ℓ) or (-) = levorotatory, rotates the plane of polarized light to the left.
- Optical Isomerism: They can exist in more than one form (isomers).
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Optical Activity: They rotate the plane of polarized light.
Specific Rotation
- For a fixed concentration and tube length, the angle of rotation depends only on the substance. This is called specific rotation.
- The specific rotation is measured in degrees when the concentration is 100g/dL, the tube length is 10 cm, and sodium light at 20°C is used. For example, glucose has a specific rotation of (+52.5), and fructose has (-91).
Optical Isomerism
- A substance with one asymmetric carbon atom has two isomers.
- A substance with two or more asymmetric carbon atoms can exist in a number of isomers calculated by 2^n, where n is the number of asymmetric carbons.
- For example, glucose has four asymmetric carbons, resulting in 16 possible isomers.
D and L Isomers (Enantiomers)
- Enantiomers are mirror images of each other.
- They have the same structural formula but differ in their spatial configuration. They rotate polarized light equally but in opposite directions.
- Glyceraldehyde, the simplest monosaccharide, has one asymmetric carbon and two optical forms: L and D forms.
- D and L forms are classified based on the position of the -OH group attached to the carbon next to the last -CH2OH. For example, using carbon number 5 in glucose.
Anomeric Carbon and Anomers
- Anomeric carbon: The asymmetric carbon formed from the active carbonyl sugar group – carbon number 1 in aldoses and carbon number 2 in ketoses.
- Anomers: Isomers formed by changing the position of the -OH group attached to the anomeric carbon. For example, α and β glucose are two anomers.
Mutarotation
- Mutarotation is the gradual change in specific rotation of an optically active substance with a free aldehyde or ketone group.
- For example:
- Freshly dissolved α-glucose in water has a specific rotation of +112.
- Freshly dissolved β-glucose in water has a specific rotation of +19.
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Description
Test your knowledge on the classification and naming of monosaccharides! This quiz covers both aldehyde and ketone groups as well as the number of carbon atoms. Review important terms like aldoses, ketoses, and various carbon classifications.
