Chapter 8 · Chemistry
Drawing Organic Molecules: Four Ways
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One butane molecule, four ways to write it: complete, condensed, bond-line and 3D. How to read each, and how to count what a zigzag hides.
Download the short notesPDF, 178 KB · solved examples, practice set and answer key Download the workbook
PDF, 183 KB · fill in the blanks, true/false, assertion-reason, MCQ, numericals, short answer, match the columns; detailed solutions at the end Up next in this chapter
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Key points
- Complete structural formula: every atom and every bond is shown.
- Condensed formula: bonds are dropped, as in CH₃CH₂CH₂CH₃; repeated groups go in a bracket, CH₃(CH₂)₂CH₃.
- Bond-line formula: every corner and every line end is a carbon.
- H atoms on carbon are not written: each carbon has 4 bonds, and the rest are to H.
- 3D drawing: a solid wedge comes towards you, a dashed wedge goes away, a normal line lies in the plane of the paper.
Reading a bond-line formula
| Drawing | Carbons | Hydrogens | Formula |
|---|---|---|---|
| Zigzag with 4 points | 4 | 10 | C₄H₁₀ (butane) |
| Zigzag with 4 points, first bond double | 4 | 8 | C₄H₈ (but-1-ene) |
| 3-point zigzag ending in OH | 3 | 8 | C₃H₈O (propan-1-ol) |
| Hexagon | 6 | 12 | C₆H₁₂ (cyclohexane) |
Try it yourself
Goal: Decode bond-line drawings and count their carbons and hydrogens.
- Choose a molecule.
- Tap a corner or a line end to decode that carbon.
- Set your count of carbons and hydrogens, then press Check.
- Compare butane with 2-methylpropane: same formula, different drawing.
Quick quiz
3 questions. Choose an answer for each, then submit to see your score and the explanations.
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