Questions and Answers
What is the definition of optical activity?
What is the term for the study of the three-dimensional arrangement of atoms in molecules?
What is the term for non-superimposable mirror images?
What is the term for achiral molecules with a plane of symmetry?
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What is the factor that affects the degree of optical activity?
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What is the technique used to measure the degree of optical activity?
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What is the measure of the degree of optical activity, expressed in degrees per unit length?
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What is the characteristic of enantiomers?
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What system is the R/S notation based on?
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What determines the priority of atoms in the R/S notation?
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What does the 'E' in E/Z notation stand for?
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What is the older notation system based on?
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What do vertical bonds in a Fischer projection represent?
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What is the purpose of Fischer projections?
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Study Notes
Optical Activity and Stereochemistry
Definition of Optical Activity
- Optical activity is the ability of a substance to rotate the plane of polarized light
- It is a property of chiral molecules, which are non-superimposable on their mirror images
Stereochemistry and Optical Activity
- Stereochemistry is the study of the three-dimensional arrangement of atoms in molecules
- Chiral molecules have a non-superimposable mirror image, which is known as an enantiomer
- Enantiomers have the same physical and chemical properties, but rotate plane-polarized light in opposite directions
Types of Stereoisomers
- Enantiomers: non-superimposable mirror images
- Diastereomers: stereoisomers that are not mirror images
- Meso compounds: achiral molecules with a plane of symmetry
Optical Activity and Chirality
- Chiral molecules exhibit optical activity due to their asymmetric structure
- The degree of optical activity is dependent on the molecule's chirality
- Chiral molecules can rotate plane-polarized light in either a clockwise (dextrorotatory) or counterclockwise (levorotatory) direction
Factors Affecting Optical Activity
- Molecular structure: the arrangement of atoms in the molecule affects its optical activity
- Concentration: the degree of optical activity is proportional to the concentration of the chiral molecule
- Temperature: temperature changes can affect the degree of optical activity
Measurement of Optical Activity
- Polarimetry: a technique used to measure the degree of optical activity
- Specific rotation: a measure of the degree of optical activity, expressed in degrees per unit length
Optical Activity and Stereochemistry
- Optical activity is the ability of a substance to rotate the plane of polarized light, a property unique to chiral molecules.
- Chiral molecules are non-superimposable on their mirror images, meaning they cannot be overlaid on top of each other.
Stereochemistry
- Stereochemistry is the study of the three-dimensional arrangement of atoms in molecules.
- Chiral molecules have a non-superimposable mirror image, known as an enantiomer.
Stereoisomers
- Enantiomers are non-superimposable mirror images, rotating plane-polarized light in opposite directions.
- Diastereomers are stereoisomers that are not mirror images.
- Meso compounds are achiral molecules with a plane of symmetry.
Chirality and Optical Activity
- Chiral molecules exhibit optical activity due to their asymmetric structure.
- The degree of optical activity depends on the molecule's chirality.
- Chiral molecules can rotate plane-polarized light in either a clockwise (dextrorotatory) or counterclockwise (levorotatory) direction.
Factors Affecting Optical Activity
- Molecular structure affects optical activity, as the arrangement of atoms influences the degree of optical activity.
- Concentration affects optical activity, with higher concentrations resulting in greater optical activity.
- Temperature changes can affect the degree of optical activity.
Measuring Optical Activity
- Polarimetry is a technique used to measure the degree of optical activity.
- Specific rotation is a measure of the degree of optical activity, expressed in degrees per unit length.
Stereochemical Notation
R/S Notation
- Describes the configuration of a stereocenter based on the Cahn-Ingold-Prelog (CIP) system
- R (rectus) prefix indicates decreasing priority of atoms around the stereocenter when viewed from the top
- S (sinister) prefix indicates increasing priority of atoms around the stereocenter when viewed from the top
Priority of Atoms
- Determined by the atomic number of atoms attached to the stereocenter
- Higher atomic number receives higher priority
- If atomic numbers are equal, the next atom in the chain is considered for priority
E/Z Notation
- Describes the configuration of alkenes
- E (entgegen) prefix indicates highest priority groups are on opposite sides of the double bond
- Z (zusammen) prefix indicates highest priority groups are on the same side of the double bond
D/L Notation
- Older system, still used in some cases
- Based on the relationship between a molecule and glyceraldehyde
- D indicates the same configuration as D-glyceraldehyde
- L indicates the same configuration as L-glyceraldehyde
Fischer Projections
- A 2D representation of a molecule's 3D structure
- Vertical bonds come out of the plane, while horizontal bonds go into the plane
- Used to visualize and compare molecular configurations
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Description
Learn about the definition of optical activity, its relation to chiral molecules, and the study of stereochemistry in molecules. Understand the concept of enantiomers and their properties.
