Formulas, functional groups and the naming of organic compounds

Need to know

What you need to know

• **Empirical Formula:** The simplest whole-number ratio of atoms of each element in a compound. (e.g., $CH_2O$ for glucose).
• **Molecular Formula:** The actual number of atoms of each element in one molecule of the compound. (e.g., $C_6H_{12}O_6$ for glucose).
• **Structural Formula:** Shows the arrangement of atoms in a molecule, indicating which atoms are bonded to which, but in a condensed format. (e.g., $CH_3CH_2OH$ for ethanol).
• **Displayed Formula:** Shows every atom and every bond in the molecule. It gives a 2D representation of the connectivity. (e.g., drawing out all C-H, C-C, and C-O bonds for ethanol).
• **Skeletal Formula:** A simplified representation where carbon chains are lines, and carbon/hydrogen atoms are implied. Vertices and ends of lines are carbons. Functional groups are explicitly drawn.

Explanation

The Language of Organic Molecules

1. A homologous series is a family of compounds with the same functional group and general formula, where successive members differ by a –CH₂ group.
2. Functional groups are specific atoms or groups of atoms, like –OH or –COOH, that determine a molecule's characteristic chemical reactions.
3. Apply IUPAC rules by first finding the longest continuous carbon chain, then numbering it to give the lowest possible numbers (locants) to functional groups and substituents.
4. A displayed formula shows every single atom and every single bond, whereas a skeletal formula simplifies this by representing carbon chains as zig-zag lines.