Homologous series | Organic Compounds, Functional Groups & Structural Isomers | Britannica (original) (raw)

homologous series, any of numerous groups of chemical compounds in each of which the difference between successive members is a simple structural unit. Such series are most common among organic compounds, the structural difference being a methylene group, as in the paraffin hydrocarbons, or alkanes; the normal primary alcohols, or 1-alkanols; and the normal carboxylic acids, or alkanoic acids. In each of these homologous series the number of methylene groups—designated by the subscript _n_—may have the successive values 0, 1, 2, 3, etc.

Homologous series of inorganic compounds include the phosphoric acids, the silicic acids, and the phosphonitrilic chlorides.

Within a given homologous series the chemical properties of the compounds are essentially all alike, and the physical properties vary in a continuous and predictable manner.