Introduction to Chapter 4 Organic Compounds: Structure Representation

Chapter 4: Introduction to Organic Compounds

Outline

• Representing the Structures of Organic Compounds

• Alkanes: The Simplest Organic Compounds

• Families of Organic Compounds—Functional Groups

• Nomenclature of Simple Alkanes

• Isomerism in Organic Compounds

Representing the Structures of Organic Compounds

What Are Organic Compounds?

Organic compounds are molecules primarily composed of carbon and hydrogen, but they may also contain other elements such as oxygen, nitrogen, sulfur, and phosphorus. Biomolecules—including proteins, carbohydrates, lipids, and DNA—are all examples of organic compounds.

Types of Structural Representations

• Molecular Formula: Indicates the number of each type of atom in a molecule, but does not show how the atoms are connected. Example: $C_3H_8$

• Condensed Structural Formula: Shows all atoms in a molecule but as few bonds as possible. May or may not show lone pairs. Example: $CH_3CH_2CH_3$

• Lewis Structure: Shows all atoms, all bonds, and complete connectivity, including lone pairs if relevant. Example: A full diagram with each atom and bond drawn explicitly.

Skeletal Structures

Skeletal structures (also called line-angle formulas) are simplified representations where:

• Lines represent bonds between carbon atoms.

• Carbon atoms are implied at the ends and intersections of lines.

• Hydrogen atoms bonded to carbon are not shown but are implied.

• Atoms other than carbon and hydrogen (heteroatoms) are shown explicitly with their symbols.

• Skeletal structures are typically used for compounds with three or more carbon atoms.

Rules for Drawing Skeletal Structures

• Show bonds between carbon atoms as lines.

• Do not show bonds between carbon and hydrogen; these are implied.

• Show other elements (heteroatoms) bonded to carbon at the end of the bond using their symbol.

• If heteroatoms have hydrogens attached, show these hydrogens explicitly.

• Lone pairs of electrons are not shown.

Steps for Drawing Skeletal Structures

1. Determine the number of carbons connected end to end.

2. Draw the bonds between the carbons (the carbon skeleton).

3. Draw bonds to noncarbon atoms (such as oxygen, nitrogen, halogens, etc.).

Examples of Skeletal Structures

• Hexane: A straight chain of six carbon atoms, represented as a zig-zag line with five bends (each bend or end is a carbon atom).

• Cyclohexane: A six-membered ring, drawn as a hexagon.

• Branched Alkanes: Branches are shown as lines extending from the main chain at the appropriate carbon.

Additional info: Skeletal structures are especially useful for visualizing large organic molecules and for quickly identifying functional groups and branching patterns.