General Formulae of Organic Compounds
Chemistry: Cambridge International GCSE Supplement, topic 11.1.2
General Formulae of Organic Compounds
A homologous series groups organic compounds with similar structure, same functional group, and differ by CH2 units. These include alkanes, alkenes, alcohols, and carboxylic acids.
What is a homologous series?
- A homologous series is a group of organic compounds.
- Compounds in a homologous series have similar structures.
- Each member of the series differs from the next by a -CH2- unit in the chain.
- Members have the same functional group.
- Example: Alkanes, alkenes, alcohols, carboxylic acids.
General formula of alkanes (CnH2n+2)
- Alkanes are saturated hydrocarbons.
- Alkanes only have carbon and hydrogen.
- Alkanes have single bonds only.
- The general formula is CnH2n+2.
General formula of alkenes (CnH2n)
- Alkenes are unsaturated hydrocarbons.
- Alkenes have a double bond between adjacent carbon atoms.
- The general formula is CnH2n.
- Alkenes react differently from alkanes due to double bonds.
General formula of alcohols (CnH2n+1OH)
- Alcohols contain an –OH group (hydroxyl).
- Alcohols have hydrocarbons plus OH.
- The general formula is CnH2n+1OH.
- Alcohols can dissolve in water and burn.
General formula of carboxylic acids (CnH2n+1COOH)
- Carboxylic acids have a –COOH group.
- They have the functional group carboxyl.
- The general formula is CnH2n+1COOH.
- Carboxylic acids taste sour and react with carbonates.
Test yourself on General Formulae of Organic Compounds
What is a defining characteristic of compounds within a homologous series?