Homologous Series:   In organic chemistry, homologous series is defined as a series of compounds in which there is a constant difference in the methylene (-CH2-) group between any two successive members of the family. e.g. Homologous series of alkanes,alkenes and alcohols: General characteristics of Homologous Series: There is a constant difference of methylene (-CH2-)What are Homologous Series – Organic Chemistry