The four things you must be able to read: a zig-zag chain, a ring, an alcohol, and a carbonyl — all drawn live by the same rules.
Bond-line structures are the alphabet of organic chemistry — the whole system runs on a handful of rules, each shown below with a live-rendered structure.
1. Every Vertex and Every Line End Is a Carbon
You never write "C" in the framework: each corner where lines meet and each free line end is a carbon, and the lines are the bonds.
2. Hydrogens on Carbon Are Implied — Fill Every Carbon to Four Bonds
Carbon makes exactly four bonds, so count the lines touching each carbon and add enough hydrogens to reach four.
- 1 line to a carbon → 3 implied H (a CH3, always a chain end).
- 2 lines → 2 implied H (a CH2).
- 3 lines → 1 implied H (a CH).
- 4 lines → 0 implied H (a fully substituted, "quaternary" carbon).
Hexane is 2×CH3 ends + 4×CH2 = C6H14; cyclopentane is five identical CH2 = C5H10 — no H drawn, formula fully determined.
3. Every Non-Carbon Atom — and the Hydrogens on It — Are Drawn Explicitly
Heteroatoms (O, N, S, halogens) are written with their symbol and their own hydrogens filled to normal valence — O wants 2 bonds, N wants 3, a halogen wants 1.
4. Double and Triple Bonds Are Just Extra Parallel Lines
Two parallel lines are a double bond, three a triple — and each uses up that many of a carbon's four bonds, so subtract them before adding implied H.
5. Chains Zig-Zag and Rings Are Polygons
Kink chains at ~120° so each carbon shows as its own vertex, and draw rings as polygons; benzene is a hexagon with three alternating double bonds, C6H6.
6. Convert Between Formulas and Skeletons — and Count Atoms Directly
You'll constantly move between three notations:
- Lewis / full structural — every atom and bond shown (best for tracking electrons, slow to draw).
- Condensed — one line, e.g. CH3CH2OH, each carbon grouped with its hydrogens.
- Bond-line — the skeletal zig-zag on this page (fastest, cleanest for mechanisms).
Condensed → bond-line: one vertex per carbon, drop C–H hydrogens, keep heteroatoms — CH3CH(OH)CH3 is isopropanol. Bond-line → formula: count vertices, fill implied H, add heteroatoms; chlorocyclohexane gives C6H11Cl.
7. Summary
Vertices and ends are carbons · hydrogens on carbon are implied, fill to four bonds · heteroatoms and their H are drawn · double/triple bonds are extra parallel lines that eat the bond budget · chains zig-zag, rings are polygons.
Quiz yourself
Tap a question to reveal the answer — free, no login.
Four segments make a chain of 5 carbons (two free ends + three internal vertices) — this is pentane. The two ends are CH3 (3 H each) and the three inner vertices are CH2 (2 H each): 6 + 6 = 12 hydrogens, so C5H12.
The "leave hydrogens off" rule applies only to hydrogens bonded to carbon. Oxygen is a heteroatom, so it and any hydrogen attached to it are drawn explicitly. The O–H hydrogen is chemically important (acidity, hydrogen bonding), so it's never left implicit.
Two. A double bond counts as two of carbon's four bonds, so 4 − 2 = 2 implied hydrogens — a terminal =CH2. Counting the double bond as a single bond (and writing 3 H) is the most common mistake here.
Two carbons → a two-vertex line (one short segment). Drop the carbon hydrogens, but keep the nitrogen: write "NH2" at the end of the line. That's ethylamine — a single zig-zag segment tipped with NH2.
Draw this on the whiteboard
Open the OChem Board whiteboard — benzene rings, curved arrows, wedge/dash bonds and a clickable periodic table built in. No account needed.