Homologous series
In chemistry, homologous series is a series of organic compounds with similar chemical properties, members of which differ by a constant relative molecular mass.
Alkanes (paraffins), alkenes (olefins), and alkynes (acetylenes) form such series in which members differ in mass by 14, 12, and 10 atomic mass units, respectively. For example, the alkane homologous series begins with methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10), and pentane (C5H12), each member differing from the previous one by a CH2 group (or 14 atomic mass units).
Compounds in each set have the same little group of atoms called the functional group. Most chemical properties of organic compounds are due to the presence of the functional group.
| Homologous Series | General Formula | Example | Functional Group |
| Alkanes | CnH2n+2 (n more than or equal to 1) | CH4, n=1 | |
| Alkenes | CnH2n (n more than or equal to 2) | C2H4, n=2 | C = C |
| Alcohols | CnH2n+2O (n more than or equal to 1) | CH4O, n=1 | - OH |
| Carboxylic Acids | CnH2nO2 (n more than or equal to 1) | CH2O2, n=1 | - COOH |
Where n represents the number of carbon atoms.