Overview
This lecture revisits isomers, distinguishing between structural (constitutional) isomers and stereoisomers, and their respective subcategories with examples.
Types of Isomers
- Isomers have identical molecular formulas but different structures.
- Two main types: structural (constitutional) isomers and stereoisomers.
Structural (Constitutional) Isomers
- Structural isomers have the same molecular formula but differ in atomic connectivity.
- Example: Two hydrocarbons with formula C₅H₁₂; one has a five-carbon chain, the other a four-carbon chain with a branch.
Stereoisomers
- Stereoisomers share both molecular formula and connectivity but differ in spatial arrangement.
- Two subtypes: enantiomers and diastereomers.
Enantiomers
- Enantiomers are non-superimposable mirror images.
- Example: Molecules with a stereogenic carbon bonded to four different groups; mirror images are different and not superimposable.
Diastereomers
- Diastereomers are stereoisomers that are not mirror images of each other.
- Examples: Cis-trans (Z/E) isomers, conformational isomers (eclipsed or staggered), and meso compounds.
Distinguishing Isomers and Stereoisomers
- "Isomer" is a broad term, subdivided into structural isomers and stereoisomers.
- Stereoisomer is a type of isomer, but not all isomers are stereoisomers.
Key Terms & Definitions
- Isomer — Compounds with the same molecular formula but different structures.
- Structural (Constitutional) Isomer — Isomers differing in the connectivity of atoms.
- Stereoisomer — Isomers with the same connectivity but differing spatial arrangement.
- Enantiomer — Stereoisomers that are non-superimposable mirror images.
- Diastereomer — Stereoisomers that are not mirror images (includes cis-trans, conformational, and meso compounds).
- Stereogenic Carbon — A carbon atom bonded to four different groups.
Action Items / Next Steps
- Review examples of each isomer type.
- Practice drawing structural and stereoisomers for assigned molecules.