Hydrocarbons are organic compounds that contain only hydrogen and carbon atoms. They form the basic structure of all other organic compounds and are mainly obtained from petroleum, natural gas, and coal.

General Properties of Hydrocarbons

1. They are generally non-polar and insoluble in water.

2. They dissolve in organic solvents such as benzene or ether.

3. They have low melting and boiling points which increase with molecular mass.

4. Hydrocarbons undergo combustion to form CO₂ and H₂O.

5. Saturated hydrocarbons are less reactive than unsaturated hydrocarbons.

6. Alkenes and alkynes undergo addition reactions.

7. Aromatic hydrocarbons undergo electrophilic substitution.

Hydrocarbons are classified into:
• Aliphatic hydrocarbons
• Alicyclic (cyclic) hydrocarbons
• Aromatic hydrocarbons

These are open-chain hydrocarbons. They can be straight-chain or branched-chain. They are subdivided into alkanes, alkenes, and alkynes.

Alkanes are saturated hydrocarbons containing only single covalent bonds.

Example 1: Methane

    H
    |
H – C – H
    |
    H
  

Example 2: Butane

CH₃–CH₂–CH₂–CH₃
  

Alkenes are unsaturated hydrocarbons containing at least one carbon–carbon double bond.

Example 1: Ethene

H₂C = CH₂
  

Example 2: But-2-ene

CH₃–CH = CH–CH₃
  

Alkynes are unsaturated hydrocarbons that contain at least one triple bond.

Example: Ethyne

HC ≡ CH
  

Alicyclic hydrocarbons are a type of hydrocarbon that contains a ring of carbon atoms, which can be saturated (cycloalkanes) or unsaturated (cycloalkenes and cycloalkynes). Examples include cyclopropane, cyclobutane, and cyclohexene. These compounds exhibit unique properties due to their ring structure, such as stability and reactivity patterns distinct from their acyclic counterparts.

Example: Cyclohexane

      CH₂
   /       \
CH₂         CH₂
 |           |
CH₂ ——————— CH₂
  

Example: Cyclopropene

   CH₂
  /   \
  C = C
  

These are compounds that contain the benzene ring and exhibit aromatic character. They generally undergo substitution reactions instead of addition.

Example 1: Benzene (C₆H₆)

     CH2
    //  \
   C     CH
  ||     ||
  HC     C
    \   /
     CH2

Example 2: Toulene C₆H₅(CH₃)

Example 3: Phenol C₆H₅(OH)