Root names give the number of carbons in the longest continuous chain. Root names are used with various "endings" to indicate branches, type of bonds between carbons, and functional groups. The following list gives the most basic root the with normal hydrocarbon alkane endings for the number of carbons in the longest continuous chain. MEMORIZE THIS LIST. Example: root = "hex" + alkane ending = "ane" = hexane. See on left.
The longest continuous chain of carbons is found by tracing through carbons without lifting your pencil or "backing up". Hydrogens, although written between carbons in condensed formulas, do not break the carbon chain. An oxygen, nitrogen, or sulfur between carbons DOES break the continuous carbon chain. The longest continuous chain may turn in any direction.
Example lower left: Initially you may think that the six carbons in a straight line is the longest chain. Look again and count the red carbons to find seven carbons as the longest chain to give heptane as the root name.
No. of Carbons	Root Name	Formula CnH2n+2	Structure
1	methane	CH4	CH4
2	ethane	C2H6	CH3CH3
3	propane	C3H8	CH3CH2CH3
4	butane	C4H10	CH3CH2CH2CH3
5	pentane	C5H12	CH3CH2CH2CH2CH3
6	hexane	C6H14	CH3CH2CH2CH2CH2CH3
7	heptane	C7H16	CH3CH2CH2CH2CH2CH2CH3
8	octane	C8H18	CH3CH2CH2CH2CH2CH2CH2CH3
9	nonane	C9H20	CH3CH2CH2CH2CH2CH2CH2CH2CH3
10	decane	C10H22	CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3