BMS1011 WK2L2 Part A flashcards

Introduction to Chirality

• Chirality refers to the three-dimensional orientation of molecules and the importance of their mirror images.

• Chirality is significant in chemistry, particularly because most biological molecules exhibit chirality.

• Understanding chirality is essential for discussing sugars, amino acids, and their functions in biological systems.

Learning Outcomes

• Familiarity with:

  • Isomers and their definitions

  • Constitutional isomers vs stereoisomers

  • Cis-trans isomers

  • Stereocenters, enantiomers, and diastereoisomers

  • Nomenclature for stereocenters (R/S system)

  • Biological relevance of chirality

Isomers

• Definition: Isomers are molecules with the same molecular formula but different arrangements of atoms in space.

• Types of Isomers:

  • Constitutional Isomers: Differ in the connectivity of atoms.

    • Examples include variations in carbon skeletons (e.g., butane vs. isobutane).

  • Stereoisomers: Atoms are bonded in the same order but differ in their three-dimensional orientation.

    • Can include configurations that are described with specific annotations in models (e.g., bold lines represent bonds coming out of the plane, dashed lines represent bonds going behind the plane).

Constitutional Isomers

• Examples of constitutional isomers:

  • Butane (C4H10) can exist as a straight-chain or branched chain (isobaric isoalkane).

  • Different constitutional isomers can demonstrate distinct physical properties, such as boiling points:

    • Butane: -0.5°C

    • Isobutane: -11.6°C

  • Ethanol (C2H5OH) vs. Dimethyl Ether (C2H6O): Ethanol has a boiling point of 78°C due to hydrogen bonding, whereas dimethyl ether has a boiling point of -24°C due to lack of hydrogen bonds.

  • Importance of structures in organic chemistry: Formulas can be misleading; understanding the structure is critical for predicting chemical behavior.

Stereoisomers

• Definition: Stereoisomers retain the same connectivity but differ in spatial orientation.

• Cis-Trans Isomers: Common in alkenes due to restricted rotation around double bonds.

  • Cis Isomer: Substituents are on the same side of the double bond.

  • Trans Isomer: Substituents are on opposite sides of the double bond.

• In cases with different substituents, we introduce the concept of priorities (according to atomic numbers).

  • E/Z Nomenclature:

    • E (Entgegen): Higher priority substituents are on opposite sides (analogous to trans).

    • Z (Zusammen): Higher priority substituents are on the same side (analogous to cis).

• Priority is determined by comparing the atomic numbers of the substituents directly attached to the double-bonded carbons.

Summary of Key Concepts

• Chirality is a critical aspect of molecular structure with far-reaching implications in chemistry and biology.

• Understanding isomerism, especially chirality, is pivotal for the study of organic compounds and biological interactions.

• Familiarity with naming conventions for stereoisomers (E/Z, R/S) enhances clarity in communication about molecular structures.