IB CHEMISTRY

Structure 3.2.3

Homologous Series

A family of compounds in which successive members differ by a common structural unit.

key Characteristics

  • Same Functional Group: Determines the chemical properties.
  • Same General Formula: A mathematical formula for the entire series.
  • Differ by āˆ’CH2āˆ’-CH_2-: Each successive member adds one methylene unit.
  • Gradation in Physical Properties: Predictable trends in boiling point, density, etc.
  • Similar Chemical Properties: They react in similar ways (e.g., all alcohols oxidize).

General Formulas

Alkanes

CnH2n+2C_nH_{2n+2}

Alkenes

CnH2nC_nH_{2n}

Alkynes

CnH2nāˆ’2C_nH_{2n-2}

Alcohols

CnH2n+1OHC_nH_{2n+1}OH

Carboxylic Acids

CnH2n+1COOHC_nH_{2n+1}COOH

Aldehydes

CnH2n+1CHOC_nH_{2n+1}CHO