Hydrocarbons are organic compounds composed solely of carbon and hydrogen, serving as primary energy sources (LPG, CNG, petrol) and petrochemical raw materials. Classified into aliphatic (alkanes, alkenes, alkynes) and aromatic, they are categorized by saturation—saturated (single bonds) or unsaturated (double/triple bonds).

Key Concepts for NEET
Classification:
Aliphatic/Acyclic: Open chains, including saturated Alkanes (
) and unsaturated Alkenes (
) & Alkynes (
).
Alicyclic: Closed chains (rings) without aromatic character (e.g., Cycloalkanes).
Aromatic: Contains benzene or similar rings with localized/delocalized
electrons.
Physical Properties: Generally colorless, weak-odored, and non-polar (hydrophobic). Lower hydrocarbons are gases; higher ones are liquids/solids. Melting/boiling points increase with molecular weight and decrease with branching.
Key Reactions & Properties:
Alkanes: Known as paraffins (low reactivity), undergoing substitution reactions (e.g., halogenation).
Alkenes/Alkynes: High reactivity due to
bonds, prone to electrophilic addition reactions.
Aromatic: Primarily undergo electrophilic substitution reactions, not addition.
Preparation & Stability: Key preparation methods include Decarboxylation of fatty acids, Wurtz reaction, and catalytic hydrogenation. Stability is generally determined by hyperconjugation and resonance.
Important Notes
LPG contains propane and butane, while CNG is primarily methane.
Higher hydrocarbons are used as solvents for paints.
Isomerism: Alkanes exhibit chain, position, and conformational isomerism.