Homolog
Definition and meaning of Homolog in chemistry.
Homolog refers to any member of a homologous series, a group of organic compounds with the same functional group and general formula whose successive members differ by a constant CH2 unit.
In more detail
Because homologs share the same functional group, they undergo similar characteristic reactions and can be described by one general formula, such as CnH2n+2 for alkanes. Physical properties, including boiling point, melting point, and density, change gradually and predictably as the carbon chain lengthens, since each added CH2 unit increases molar mass by about 14 atomic mass units. This regular gradation allows chemists to predict the properties of an unknown member of a series once a few members have been studied.
Key facts
| Field | Organic Chemistry |
|---|---|
| Constant difference | CH2 (adds ~14 u per step) |
| Example series | Alkanes, CnH2n+2 |
| Shared trait | Same functional group and general formula |
Methane (CH4) and ethane (C2H6) are homologs: both are alkanes, and ethane's formula differs from methane's by exactly one CH2 unit.
Frequently asked questions
Are homologs chemically identical?
No, only similar. They share the same functional group and undergo the same types of reactions, but reaction rates and some physical properties shift gradually as chain length increases.
How do homologs differ from isomers?
Homologs have different molecular formulas that differ by a CH2 unit; isomers share the exact same molecular formula but differ in structural arrangement.