2.1 Representing Molecules
There are many ways to represent organic molecules. Understanding these different representations is essential for communicating chemical structures.
Condensed Structural Formula: Shows how atoms are connected using grouped atoms. Carbons and their attached hydrogens are written in small groups (e.g., CH₃, CH₂).
Key Rules for Condensed Formulas
- Each carbon and its attached H atoms are written together (CH₃, CH₂, CH)
- Bonds between carbons are implied, not drawn
- Branches can be shown in parentheses: CH₃CH(CH₃)CH₃
- Multiple identical groups: (CH₃)₂CH means two CH₃ groups attached
Bond-line Structure (Skeletal Structure): The most common way to draw organic molecules. Carbon atoms are at vertices and line ends; hydrogens on carbon are not shown.
5 Rules for Bond-Line Structures
1
Carbons are at every vertex (corner) and at the end of every line
2
Hydrogens attached to carbon are NOT shown (they're implied)
3
All heteroatoms (N, O, S, halogens) MUST be shown
4
Hydrogens attached to heteroatoms MUST be shown
5
Assume enough H atoms to give each carbon 4 bonds