H

Homologous Series

CₙH₂ₙ₊₂ → CₙH₂ₙ₊₄ (differ by CH₂)
Quick Reference
Formula / NotationCₙH₂ₙ₊₂ → CₙH₂ₙ₊₄ (differ by CH₂)
Also Known AsHomologous series, homologs, alkane series, functional group series

What is Homologous Series?

A series of organic compounds with the same functional group and general formula, differing from each other by a -CH₂- unit. Each member has similar chemical properties but gradually changing physical properties. Examples include the alkanes (CₙH₂ₙ₊₂) and alcohols.

Formula & Notation

CₙH₂ₙ₊₂ → CₙH₂ₙ₊₄ (differ by CH₂)

Other Names / Synonyms: Homologous series, homologs, alkane series, functional group series

Properties & Characteristics

A homologous series is a family of organic compounds with the same general formula, the same functional group, and similar chemical properties, in which consecutive members differ by a CH₂ unit (14 mass units). Physical properties (boiling point, density, viscosity) change regularly with increasing chain length. Alkanes (CₙH₂ₙ₊₂), alkenes (CₙH₂ₙ), alkynes (CₙH₂ₙ₋₂), alcohols (CₙH₂ₙ₊₁OH) are classic homologous series.

Uses & Applications

The homologous series concept allows prediction of physical and chemical properties of unsynthesised compounds by interpolation or extrapolation from known members. It is the basis for understanding trends in detergent chain length (solubility/emulsification balance), biodegradability with chain length, and polymer backbone chemistry.

Safety Information

Within a homologous series, toxicity and flammability generally change with chain length: short-chain alkanes are more volatile (lower LEL) and more potent narcotic; longer chains are less volatile but more persistent environmental contaminants. Never assume all members of a series are equally hazardous.

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term Homologous Series
Formula CₙH₂ₙ₊₂ → CₙH₂ₙ₊₄ (differ by CH₂)
Synonyms Homologous series, homologs, alkane series, functional group series

Frequently Asked Questions

A series of organic compounds with the same functional group and general formula, differing from each other by a -CH₂- unit. Each member has similar chemical properties but gradually changing physical properties. Examples include the alkanes (CₙH₂ₙ₊₂) and alcohols.

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