Class 11 Chemistry – Hydrocarbons
CBSE 2026–27 | NCERT-aligned free study resource
Introduction
Hydrocarbons contain only carbon and hydrogen. Major classes include alkanes, alkenes, alkynes and aromatic hydrocarbons.
Alkanes
Alkanes are saturated hydrocarbons with single bonds. They commonly undergo substitution reactions, especially halogenation under suitable conditions. Conformations arise from rotation about single bonds.
Alkenes
Alkenes contain carbon-carbon double bonds and commonly undergo addition reactions. Electrophilic addition and Markovnikov’s rule are important concepts.
Alkynes
Alkynes contain carbon-carbon triple bonds. Addition reactions occur across the multiple bond, and terminal alkynes show characteristic acidity relative to alkanes.
Aromatic Hydrocarbons
Benzene is an aromatic hydrocarbon with a delocalised π-electron system. Aromatic compounds commonly undergo electrophilic substitution reactions.
Environmental and Safety Perspective
Combustion of hydrocarbons releases energy but can produce carbon monoxide and other pollutants under incomplete combustion. Safe handling and responsible use are important.
MCQs
- Alkanes are: (A) saturated (B) unsaturated (C) ionic salts (D) metals. Answer: A.
- Ethene mainly undergoes: (A) addition reactions (B) neutralisation only (C) precipitation only (D) nuclear reactions. Answer: A.
- Benzene is classified as: (A) aromatic hydrocarbon (B) alkane (C) alkyne (D) alcohol. Answer: A.
Practice
- Write structures and IUPAC names of simple hydrocarbons.
- Distinguish addition and substitution reactions.
- Explain Markovnikov’s rule with a suitable example.
HOTS
Why do alkenes generally undergo addition more readily than alkanes? Relate your answer to the nature of the π bond.
Revision
Alkanes = single bonds; alkenes = double bonds; alkynes = triple bonds; benzene = aromatic delocalised system.