Chemistry · General Principles Of Organic Chemistry · NEET
A condensed formula still writes every carbon and hydrogen as letters, but leaves out most bond dashes and uses subscripts for repeated groups, for example CH3CH2CH2CH3 or CH3(CH2)2CH3 for butane. A bond-line formula writes no C or H letters at all for the chain: it is just a zig-zag of lines. In bond-line, every corner (bend) and every free end of a line is a carbon atom, and you mentally add enough hydrogens to give each carbon four bonds. So condensed = letters, few or no dashes; bond-line = lines only, carbons and their hydrogens are implied.
In a bond-line (skeletal) formula, carbon and hydrogen atoms are not shown for the carbon chain. Each point where two lines meet (a corner of the zig-zag) is one carbon atom, and each end of a line is also one carbon atom. After you locate a carbon, you add hydrogens so that carbon has exactly four bonds. Example: a simple zig-zag with 4 line-segments has 5 carbons. Only heteroatoms (like O, N, Cl) and the hydrogens attached to them are written openly.
Write each carbon separately and draw a dash for every bond. Take CH3(CH2)6CH3: the (CH2)6 means six CH2 units in a row, so the full chain is CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH3, and then you draw a C-H dash for each hydrogen too. The complete (dash) formula shows every single bond as a line, so nothing is hidden. This is the NCERT skill in section 8.3.1: convert between condensed and complete forms without changing the actual connectivity.
Carbon is always tetravalent (four bonds). So once you know how many bonds a carbon already has to other carbons or heteroatoms, the number of hydrogens is fixed and does not need to be drawn. If a corner carbon shows two lines to neighbours, it must have 2 hydrogens (2 + 2 = 4). This is why chemists prefer bond-line formulas for large molecules: they are fast to draw and the hydrogens are automatic. Note that hydrogens on oxygen or nitrogen ARE written, because those atoms are shown.
A cyclic compound is drawn as a closed polygon. A triangle is cyclopropane (3 carbons), a square is cyclobutane (4 carbons), a pentagon is cyclopentane (5 carbons), and a hexagon is cyclohexane (6 carbons). Each corner of the polygon is a carbon with its implied hydrogens. A double bond inside the ring is shown by a second parallel line on one edge. NCERT shows these cyclic bond-line formulas right after the open-chain ones in section 8.3.1.
Choose the correct skeletal (bond-line) structure for 2,6-dimethyldec-4-ene.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
No. A molecular formula (like C5H10) only tells you how many atoms of each element are present. A bond-line formula tells you how those atoms are connected, showing the actual shape of the chain or ring. Two different molecules can share one molecular formula but have different bond-line structures (isomers).
Bond-line (skeletal) formulas dominate reaction schemes and larger molecules because they are compact, while condensed formulas are common for short chains in options. NEET expects you to move quickly between all three, especially to count carbons and hydrogens from a bond-line drawing.
Yes. Only the hydrogens attached to carbon are left out. Because oxygen and nitrogen are drawn as letters (O, N), the hydrogens bonded to them, like the H in -OH or -NH2, must be written explicitly.
A continuous open zig-zag chain of n line segments (bonds) has n+1 carbons, because carbons sit at both ends and at every corner. For example, 4 segments give 5 carbons (pentane skeleton).
It is the fully expanded picture where every bond, including every C-H bond, is drawn as a dash (line). It hides nothing, so it is the clearest for beginners but the slowest to draw, which is why condensed and bond-line shorthands exist.
