Bond line formula or zig-zag formula

A bond-line (or zig-zag) formula goes a step further than a condensed formula by dropping the element symbols for carbon and hydrogen entirely, keeping only the bond lines themselves. Every carbon-carbon bond is drawn as a segment of a zig-zag line; each of the TWO END points of that zig-zag line represents a terminal methyl (CH3) group, and every INTERNAL vertex (every point where the line changes direction, i.e. every 'kink') represents one carbon atom, understood to be carrying however many hydrogen atoms are needed to bring it up to its normal four bonds (its tetravalency). Propane, CH3-CH2-CH3, is therefore drawn as just a simple two-segment zig-zag line -- no atom symbols at all are needed, since both end vertices are automatically read as CH3 and the one middle vertex is automatically read as CH2. The one deliberate exception to 'omit everything except carbon skeleton bonds' is that heteroatoms (any atom that is not carbon or hydrogen) are always written out in full, and so is any hydrogen that happens to be bonded directly to such a heteroatom -- so ethanol, C2H5OH, is drawn as a …