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Questions and Answers
Which of the following is a characteristic of a meso compound?
Which of the following is a characteristic of a meso compound?
What is the primary reason why humans can only metabolize the D-isomers of monosaccharides?
What is the primary reason why humans can only metabolize the D-isomers of monosaccharides?
What is the term for a molecule with multiple chiral centers that is superimposable on its mirror image?
What is the term for a molecule with multiple chiral centers that is superimposable on its mirror image?
What is the term for a molecule that cannot be superimposed on its mirror image?
What is the term for a molecule that cannot be superimposed on its mirror image?
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What is the term for a stereoisomer that is a nonsuperimposable mirror image?
What is the term for a stereoisomer that is a nonsuperimposable mirror image?
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Why are meso compounds optically inactive?
Why are meso compounds optically inactive?
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What is the term for a carbon atom that has four different groups attached to it?
What is the term for a carbon atom that has four different groups attached to it?
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What is the primary reason why most animals are only able to utilize the L-isomers of amino acids?
What is the primary reason why most animals are only able to utilize the L-isomers of amino acids?
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What is the term for compounds that have the same structural formula but different spatial arrangements of atoms?
What is the term for compounds that have the same structural formula but different spatial arrangements of atoms?
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What is the term for a stereoisomer that is a nonsuperimposable non-mirror image?
What is the term for a stereoisomer that is a nonsuperimposable non-mirror image?
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Study Notes
Chiral Carbons of Glucose
- Glucose has 4 chiral carbons: C2, C3, C4, and C5.
- The presence of a single chiral carbon gives rise to stereoisomerism.
- A carbon atom is chiral if it is attached to four different groups.
- If any two groups are identical, the carbon is not chiral.
Chirality
- Compounds can have more than one chiral carbon.
- The maximum number of stereoisomers is 2n, where n is the number of chiral carbon atoms.
- Glucose has 2^4 or 16 stereoisomers.
Fischer Projections
- Fischer Projections depict three-dimensional shapes for chiral molecules.
- The chiral carbon is represented by the intersection of two lines.
- Fischer Projections of carbohydrates have the carbonyl (C=O) group at the top.
- The two horizontal bonds are coming toward the viewer out of the plane in which they are drawn.
- The bottom carbon group is projecting away from the viewer.
D and L Enantiomers
- The hydroxyl group on the chiral carbon farthest from the C=O group determines whether the carbohydrate is D or L.
- D-Glucose and L-Glucose are enantiomers.
- The physical properties of D and L enantiomers are generally the same.
- The exception is the way solutions of the two compounds affect polarized light.
Enantiomer Properties
- Specific Rotation [α] is a fundamental property of chiral substances that is expressed as the angle to which the material causes polarized light to rotate at a particular temperature, wavelength, and concentration.
- Optical Activity is the property of rotating the plane of polarized light.
- Measurements of optical activity are useful for differentiating between enantiomers.
- Levorotatory enantiomers rotate polarized light to the left (-), while dextrorotatory enantiomers rotate polarized light to the right (+).
- Racemic Mixture is composed of dextrorotatory and levorotatory forms of a compound in equal proportion.
Importance of Carbohydrates
- Carbohydrates provide energy through their oxidation.
- They supply carbon for the synthesis of cell components.
- They serve as a stored form of chemical energy.
- They form a part of the structural elements of some cells and tissues.
Classification of Carbohydrates
- Carbohydrates are classified according to size: monosaccharides, disaccharides, and polysaccharides.
- Monosaccharides are single polyhydroxy aldehyde or ketone units.
- Disaccharides are composed of two monosaccharide units.
- Polysaccharides are very long chains of linked monosaccharide units.
Stereochemistry
- Stereoisomers are compounds with the same structural formula but different spatial arrangements of atoms.
- Enantiomers are stereoisomers that are non-superimposable mirror images.
- Diastereomers are stereoisomers that are non-superimposable non-mirror images.
- Many carbohydrates exist as enantiomers.
Chirality
- An object or system is chiral if it is distinguishable from its mirror image.
- A chiral object cannot be superimposed on its mirror image.
- A chiral carbon is one that has four different groups attached to it.
- If any two groups are identical, the carbon is not chiral.
Meso Compounds
- A meso compound is a molecule with multiple chiral centers that is superimposable on its mirror image.
- Meso compounds have a minimum of two chiral carbons, with at least one on each side of the internal mirror plane.
- Meso compounds are achiral and cannot have an enantiomer.
- Meso compounds are optically inactive.
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Description
Learn about chiral carbons in glucose, stereoisomerism, and the maximum number of stereoisomers in a compound with multiple chiral carbon atoms.
