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Question 1

What are the key concepts of optical activity in chiral compounds?

Answer 1

Rotation Directions:
Clockwise rotation: Compound is dextrorotatory (d or +).
Counterclockwise rotation: Compound is levorotatory (l or -).
Enantiomers and Rotation:
Enantiomers rotate plane-polarized light equally but in opposite directions.
Example: If one enantiomer rotates light by +5°, the other rotates it by -5°.
R/S vs. +/- Designations:
No relationship exists between R/S prefixes and the +/− optical rotation designations.

Question 2

What is a racemic mixture, and why is it optically inactive?

Answer 2

A racemic mixture (or racemate) contains equal amounts of two enantiomers.
It is optically inactive because:
Enantiomers rotate plane-polarized light by equal amounts but in opposite directions.
These rotations cancel each other out, resulting in no net rotation of the light.

Question 3

How do the physical properties of a racemic mixture compare to its individual enantiomers?

Answer 3

Melting Point: May differ from the melting points of individual enantiomers (A or B).
Boiling Point: May differ from the boiling points of individual enantiomers.
Optical Rotation: Racemic mixtures are optically inactive because the optical rotations of enantiomers (equal in magnitude but opposite in sign) cancel out, resulting in a net rotation of 0°.

Question 4

What is specific rotation and how is it calculated?

Answer 4

Question 5

What is enantiomeric excess (ee) and how is it calculated?

Answer 5

Question 6

How can enantiomeric excess (ee) be calculated using specific rotation values?

Answer 6

Question 7

Key Points on Physical Properties of Stereoisomers

Answer 7

Question 8

Chemical Properties of Enantiomers

Answer 8

Chemical Properties:
Enantiomers have identical chemical properties except for their interactions with chiral, non-racemic reagents.
This distinction arises due to their three-dimensional arrangement and their ability to interact differently with chiral environments.
Chirality in Drugs:
Many drugs are chiral and rely on specific interactions with chiral receptors or enzymes in the body.
The efficacy and safety of a drug can differ significantly between its enantiomers.
Examples:
(S)-Ibuprofen: Effective as an anti-inflammatory agent.
(R)-Fluoxetine: An active antidepressant.
(S)-Naproxen: Anti-inflammatory agent, while its enantiomer (R)-Naproxen can be toxic to the liver.