Cambridge O Level Chemistry · Syllabus 5070 · Organic Chemistry
Homologous Series
What is Homologous Series?
A family of organic compounds that share the same functional group and the same general formula, whose successive members differ by a CH2 unit, which show a gradual trend in physical properties and which have similar chemical properties.
This definition is part of the Organic Chemistry chapter in Cambridge O Level Chemistry.
Homologous Series in context
A homologous series is a family of organic compounds that share the same functional group and the same general formula, whose successive members differ by a -CH2- unit and show a gradual trend in physical properties with similar chemical properties. Alkanes (CnH2n+2) are saturated hydrocarbons with only single bonds and limited reactivity; alkenes (CnH2n) are unsaturated, containing a reactive C=C double bond; alcohols (CnH2n+1OH) contain -OH; and carboxylic acids (CnH2n+1COOH) contain -COOH and behave as acids. Substitution replaces one atom and displaces another; addition opens a double bond to form a single product; condensation polymerisation releases a small molecule at each linkage, while addition polymerisation releases nothing.