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Questions and Answers
What are stereoisomers?
What are stereoisomers?
Compounds that differ from each other only in the three-dimensional, spatial arrangement of their atoms, but not in the connectivity of their atoms.
What are isomers?
What are isomers?
Compounds that are constructed from the same atoms (same molecular formula) but that differ from each other.
What are the two types of isomers?
What are the two types of isomers?
Constitutional isomers and stereoisomers.
What are constitutional isomers?
What are constitutional isomers?
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What are stereoisomers?
What are stereoisomers?
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Do double bonds (pi-bonds) experience free rotation like single bonds (sigma bonds)?
Do double bonds (pi-bonds) experience free rotation like single bonds (sigma bonds)?
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What does trans mean?
What does trans mean?
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What does superimposable mean?
What does superimposable mean?
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What are chiral objects?
What are chiral objects?
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What is the most common source of molecular chirality?
What is the most common source of molecular chirality?
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What is an enantiomer?
What is an enantiomer?
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How to determine if a molecule is clockwise or counterclockwise?
How to determine if a molecule is clockwise or counterclockwise?
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If 1-2-3 is counterclockwise, how is the molecule designated?
If 1-2-3 is counterclockwise, how is the molecule designated?
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What does [alpha] stand for?
What does [alpha] stand for?
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What is specific rotation dependent on?
What is specific rotation dependent on?
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Are racemic mixtures optically active?
Are racemic mixtures optically active?
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What does it mean to be optically pure?
What does it mean to be optically pure?
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Do diastereomers have the same physical properties (BP, MP, etc.)?
Do diastereomers have the same physical properties (BP, MP, etc.)?
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What is the maximum number of stereoisomers?
What is the maximum number of stereoisomers?
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Study Notes
Stereoisomers and Isomers
- Stereoisomers: Compounds that differ only in the three-dimensional arrangement of their atoms, not in atomic connectivity.
- Isomers: Compounds with the same molecular formula but different structures.
- Two main types of isomers: Constitutional isomers (different connectivity) and Stereoisomers (same connectivity, different arrangement).
Characteristics of Isomers
- Constitutional isomers: Same molecular formula, different order of connectivity.
- Stereoisomers: Same molecular formula and connectivity, but different spatial arrangements.
Chiral and Achiral Molecules
- Chirality: A property of a molecule that is non-superimposable on its mirror image, indicated by a chiral center (a tetrahedral carbon with four different groups).
- Achiral molecules: Superimposable on their mirror images.
Rotation and Optical Activity
- Optically active compounds: Chiral compounds that rotate plane-polarized light.
- Enantiomers: Chiral molecules that are mirror images of each other, rotating light in opposite directions.
- Racemic mixture: Equal amounts of two enantiomers, resulting in no optical activity.
Assigning Configuration
- Use the Cahn-Ingold-Prelog Rules for assigning priority based on atomic number.
- With clockwise sequence (1-2-3), the designation is "R" and for counterclockwise, it is "S".
Physical Properties and Behavior
- Boiling point (BP) and melting point (MP) are not affected by the configuration of chiral centers.
- Intermolecular interactions determine physical properties; enantiomers typically have similar interactions.
Measuring Optical Activity
- Polarimeter: Device used to measure the rotation of polarized light.
- Observed rotation is dependent on both concentration (g/mL) and pathlength (dm).
- Specific rotation: [α] = α/(c*l), standardized rotation measurement.
Relationships Between Molecules
- Diastereomers: Not mirror images and have different physical properties (BP, MP).
- Enantiomeric excess: A measure of the purity of one enantiomer over another, calculated as % ee = (observed rotation / α of pure enantiomer) x 100%.
Stereoisomer Count
- Maximum number of stereoisomers = (2^n), where n is the number of chirality centers.
- Three chirality centers produce four pairs of enantiomers, while four chirality centers produce eight pairs.
Special Cases
- Meso compounds: Compounds with multiple stereocenters that possess symmetry, thus being achiral.
- Cis and trans isomers: Their relationships with chirality; trans tends to be chiral due to symmetry while cis may have planes of symmetry.
Additional Key Terms
- Inversion: Reflection about a point.
- Chiral vs. achiral: Chiral is optically active; achiral is optically inactive.
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Description
Test your understanding of stereoisomers and isomers, including their characteristics and differences. Explore concepts like chirality, optical activity, and the classification of various types of isomers. Challenge your knowledge with a variety of questions designed to deepen your grasp of these important concepts in chemistry.
