1. Define stereochemistry.
Answer: Stereochemistry is the branch of chemistry that studies the three-dimensional arrangement of atoms in molecules and how this arrangement affects their properties and reactions.
2. What is isomerism? Classify its types.
Answer: Isomerism is the phenomenon in which compounds have the same molecular formula but different arrangements of atoms.
Types:
- Structural (Constitutional) Isomerism
- Stereoisomerism
3. Differentiate between conformational and configurational isomerism.
Answer:
- Conformational isomerism: Arises due to rotation around a single bond; interconversion occurs without bond breaking.
- Configurational isomerism: Interconversion requires breaking and reforming bonds.
4. Define chirality with an example.
Answer: Chirality is the property of a molecule whose mirror image is non-superimposable on it.
Example: Lactic acid, CH₃CH(OH)COOH.
5. What is a chiral carbon atom?
Answer: A chiral carbon atom is a carbon attached to four different atoms or groups, resulting in non-superimposable mirror images.
6. Define optical activity.
Answer: Optical activity is the ability of a substance to rotate the plane of plane-polarized light.
7. What are enantiomers?
Answer: Enantiomers are stereoisomers that are non-superimposable mirror images of each other.
8. What are diastereomers?
Answer: Diastereomers are stereoisomers that are not mirror images of each other.
9. What is a meso compound?
Answer: A meso compound contains two or more chiral centers but is optically inactive due to an internal plane of symmetry.
10. Define racemic mixture.
Answer: A racemic mixture contains equal amounts of two enantiomers and shows no net optical rotation.
11. What is plane-polarized light?
Answer: Plane-polarized light is light whose vibrations occur in only one plane.
12. What is specific rotation?
Answer: Specific rotation is the optical rotation produced by a substance under standard conditions of concentration and path length.[α]=lcα
13. State the CIP priority rules.
Answer: The Cahn–Ingold–Prelog (CIP) rules assign priorities to atoms attached to a stereocenter based on their atomic numbers. Higher atomic number means higher priority.
14. What are R and S configurations?
Answer: R and S are symbols used to describe the absolute configuration of a chiral center according to CIP rules.
- R (Rectus): Clockwise priority sequence.
- S (Sinister): Counterclockwise priority sequence.
15. Differentiate between cis–trans and E–Z nomenclature.
Answer:
- Cis–trans: Used when identical groups are present around a double bond.
- E–Z: Uses CIP priority rules and can be applied to all substituted alkenes.
16. What is a Newman projection?
Answer: A Newman projection is a method of representing the spatial arrangement of atoms by viewing a molecule along a carbon–carbon single bond.
17. What are eclipsed and staggered conformations?
Answer:
- Eclipsed: Bonds on adjacent carbons align with each other; less stable.
- Staggered: Bonds are separated by 60°; more stable.
18. Define stereoselective reaction.
Answer: A stereoselective reaction produces one stereoisomer preferentially over another.
19. Define stereospecific reaction.
Answer: A stereospecific reaction is one in which the stereochemistry of the reactant determines the stereochemistry of the product.
20. What is racemization?
Answer: Racemization is the process by which an optically active compound is converted into an equal mixture of its enantiomers, resulting in loss of optical activity.
