Classification of Hydrocarbons
NCERT Reference:Chapter 9 – Hydrocarbons – Page 241 (Part I)
Quick Notes
- Hydrocarbons are organic compounds that contain only carbon and hydrogen.
- Major categories:
- Alkanes: Saturated hydrocarbons (single bonds).
- Alkenes: Unsaturated hydrocarbons with at least one double bond.
- Alkynes: Unsaturated hydrocarbons with at least one triple bond.
- Aromatic hydrocarbons (arenes): Contain one or more benzene rings.
- Saturated vs. Unsaturated:
- Saturated: Only C–C single bonds.
- Unsaturated: Have C=C or C≡C bonds.
- Open-chain vs. Cyclic:
- Open-chain (acyclic): Straight or branched chains.
- Cyclic: Atoms form a ring.
Full Notes
Hydrocarbons are the foundational compounds in organic chemistry, consisting solely of carbon and hydrogen atoms. Their classification is based primarily on the types of bonds present between carbon atoms and the structure (linear, branched, or ringed) of the carbon chain.
Open-chain (Acyclic) Hydrocarbons
These consist of carbon atoms connected in a linear or branched fashion. The chains do not form rings.
Saturated hydrocarbons (Alkanes)
All carbon atoms are linked by single bonds.
General formula: CnH2n+2
For Example:
- Ethane (CH3CH3), 2-methylpropane (CH3CH(CH3)CH3) and cylclobutane
Unsaturated hydrocarbons
Contain one or more double or triple bonds between carbon atoms.
- Alkenes (double bond): General formula: CnH2n
- Example: Ethene (C2H4)
- Alkynes (triple bond): General formula: CnH2n−2
- For Example: Ethyne (C2H2), Ethene (CH2CH2) and Propene (CH3CH2CH3)
Aromatic hydrocarbons (Arenes)
Contain one or more benzene rings, characterized by alternating double bonds (delocalized π-electrons).
Such compounds follow Hückel’s rule for aromaticity: (4n + 2) π electrons
Examples:
- Benzene (C6H6)
- Naphthalene (C10H8)
Summary
- Hydrocarbons contain only carbon and hydrogen atoms.
- Alkanes are saturated while alkenes and alkynes are unsaturated.
- Arenes are aromatic and obey Hückel’s rule.
- Hydrocarbons may be open chain or cyclic.