Classification of Hydrocarbons

Hydrocarbons

The organic compounds containing carbon and hydrogen atoms are known as a hydrocarbon. For example- Methane (CH₄), Ethane (C₂H₆), Hexane (C₆H₁₄), Benzene of aromatic hydrocarbon (C₆H₆) etc.

On the basis of structure, hydrocarbons can be broadly classified into two classes:

1. Open chain hydrocarbons (Aliphatic compounds)
2. Closed chain hydrocarbons (Cyclic compounds )

A) Open chain compounds -

The hydrocarbons, which contain atoms linked on the open chain are known as open-chain compounds. Example: n-pentane, iso-pentane, neo-pentane e.t.c.

Neo-pentane (If central atom is attached to 4 carbon atoms).

Open chain compounds are further divided into-

• Saturated hydrocarbons
• Unsaturated hydrocarbons

•Saturated hydrocarbons (alkane)

Those hydrocarbons, in which the carbon atoms are bonded to each other with a single covalent bond (-C-C-) are called saturated hydrocarbons. They are also known as alkanes. They follow general formula C_nH_2n+2(+ane suffix), where 'n' is any positive integer. For example-

If n=1, C₁H_2X1+2⇒ CH₄ (Methane)

If n=2, C₂H_2X2+2⇒ C₂H₆ (Ethane)

They are also known as paraffin. Example- Propane.

•Unsaturated hydrocarbons

Hydrocarbons, which the carbon atoms are bonded to each other with two (=C=C=), or three (-C≡C-) covalent bond and have the tendency to gain more hydrogen atoms are known as unsaturated hydrocarbons. They are two types:

• Alkene: Hydrocarbons containing a double bond between carbon atoms are known as an alkene. They have the general formula of C_nH_2n (+ene suffix). For example- C₂H₂₄, C₃H_6.
• Alkyne: Hydrocarbons containing a triple bond between carbon atoms are known as an alkyne. They have the general formula of C_nH_2n-2(+yne suffix). For example- C₂H₂, C₃H₄.

B) Cyclic or Closed chain compounds

Those hydrocarbons, which contain the ring of carbon atoms are known as cyclic ring compounds. Examples

They are further classified into Homocyclic and Heterocyclic compounds.

•Homocyclic compounds: If the cyclic organic compounds are composed of carbon atoms, they are known as homocyclic compounds or homocyclic hydrocarbons.

Example: Cyclopentane, cyclohexane.

Homocyclic hydrocarbons are further divided into-

• Aromatic hydrocarbons: Aromatic hydrocarbons are defined as "those cyclic hydrocarbons which have alternate C-C and C=C and are similar to the benzene ring in characters."
• Alicyclic hydrocarbons: Those cyclic hydrocarbons, which have no alternate C-C and C=C and similar properties to aliphatic compounds in characters, are known as alicyclic compounds.

Examples of aromatic- Benzene, naphthalene etc.

Examples of alicyclic: Cyclohexane, cyclopentane. Aromatic and alicyclic compounds

•Heterocyclic compounds: Those cyclic hydrocarbons, which are composed of carbon atoms as well as other elements like N, O, S etc. are known as heterocyclic compounds. For example-

Reference:

Adhikari, Rameshwar; Khanal, Santosh; Subba , Bimala; Adhikari, Santosh; Khatiwada, Shankar Pd. Universal Chemistry XI. First. Vol. 1st. Kathmandu: Oasis Publication, 2069.

Chaudhary, Ganga Ram; Karna, Shila Kant Lal; Sharma, Kanchan; Singh, Sanjay; Gupta, Dipak Kumar. A Textbook of Higher Secondary Chemistry XI. Ed. 2nd. Kathmandu: Vidyarthi Pustak Bhandar, 2069 (2012).