Organic Chemistry: Homologous Series

Homologous series is a series of organic compounds having the same functional group. A functional group is an atom or group of atoms that determine the chemical properties of a compound.
Compounds within a homologous series share a general formula. This formula is consistent across the group.
Characteristics of a homologous series include a graduated physical properties, meaning that the properties (like boiling point, melting point) change gradually with the increase of molecular size or mass.
Chemical properties remain consistent within a homologous series because they are determined by the functional group.
Each member of a series differs from the next by a ‘CH2’ unit. This predictable difference is referred to as increment.

Alkanes, alkenes, and alkynes are examples of homologous series that contain single, double and triple bonds respectively.
Note that alcohols and carboxylic acids are also examples of homologous series, defined by their functional groups of OH and COOH respectively.

Understand that compounds in a homologous series are named based on their number of carbon atoms and functional group.
For example, in the alkane series, ‘meth’ represents one carbon atom, ‘eth’ represents two, ‘prop’ three, ‘but’ four, and so on.
A compound’s name indicates its functional group with a suffix. For instance, alkanes end with ‘-ane’, alkenes end with ‘-ene’, and alcohols end with ‘-ol’.

Homologous series are very important in the study of organic chemistry because of their predictable behaviour based on functional group and increment.
Their consistent differences and predictable reactivity can be used to design and synthesis new compounds with desired properties.
Knowing the homologous series a compound belongs to can give a good estimate of its physical and chemical properties.
The patterned behavior and orderly graduation in properties of homologous series allow chemists to classify and organize a vast number of organic compounds.