Optical Activity and Stereochemistry

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

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.