Stereochemistry Lecture 1: Introduction to Stereochemistry

Stereochemistry

• Stereochemistry is the field of organic chemistry that aims to understand the relative spatial arrangement of atoms in molecules.
• It focuses on deducing the 3-D structure of an atom.

Isomers

• Isomers are molecules with the same molecular formula but different structural or spatial arrangements of atoms.
• This variation can lead to differences in physical or chemical properties.

Types of Isomers

Constitutional Isomers (Structural Isomerism / Skeletal Isomerism)

• They are different molecules with the same formula but connected together differently.
• They cannot be converted into each other without breaking and remaking bonds.
• All physical properties of constitutional isomers are different, including melting points, boiling points, solubility, and densities.

Types of Constitutional Isomers

• Chain isomers: molecules with the same molecular formula but different arrangements of the carbon 'skeleton'.
• Position isomers: different positions of the same functional group in the molecule.
• Functional isomers: different positions of atoms giving different functional groups.

Tautomers

• Tautomers are isomers of a compound that differ only in the position of protons and electrons.
• The carbon skeleton of the compound remains unchanged.
• Tautomerism involves a simple proton transfer in an intramolecular fashion, often acid or base catalyzed.

Keto-Enol Tautomerism

• A common process in which the 'keto' form is typically more stable, but in some instances, the 'enol' form can be more stable.

Metamerism

• Compounds having the same molecular formula but different numbers of carbon atoms (alkyl groups) on either side of a functional group (e.g., -O-, -S-, -NH-, -C(=O)-, esters, amides, etc).

Ring-Chain Isomerism

• Compounds having the same molecular formula but with one having an open chain and the others having cyclic structures.
• This phenomenon is known as ring-chain isomerism.