SS1 Chemistry Lesson Note on Hydrocarbon and its Main Classes

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TOPIC: CARBON AND ITS COMPOUNDS

CONTENTS:

1. HYDROCARBON AND ITS MAIN CLASSES
2. CRUDE OIL AND NATURAL GAS- FRACTIONAL DISTILLATION OF CRUDE OIL AND USES OF PETROLEUM FRACTIONS
3. CRACKING OF PETROLEUM FRACTIONS, REFORMING, OCTANE NUMBER AND KNOCKING
4. IMPORTANCE OF CRUDE OIL AND PETROCHEMICALS

 PERIOD 1: HYDROCARBON AND ITS MAIN CLASSES

Hydrocarbons, as the name implies, are compounds of only two elements; hydrogen and carbon. There are many such organic compounds.

Hydrocarbons are usually classified into two main groups namely, saturated and unsaturated hydrocarbons.

1. Saturated hydrocarbons (Alkanes). The alkanes have the general molecular formula C_nH_2n+2. . Members of this group include Methane, CH₄, ethane, C₂H₆, propane, C₃H₈, butane, C₄H_10. The structure of butane is given below.
2. Unsaturated hydrocarbons (Alkenes and alkynes). The alkenes have the general formula is C_nH_2n. Members of this group include ethene, C₂H₄ propene, C₃H₆ butene, C₄H₈ etc

Hydrocarbons can be classified into:

1. Aliphatic compounds
2. Aromatic compounds

Aliphatic compounds are classified into two sub-classes:   1. Acyclic compounds   2. Cyclic compounds

In acyclic compounds the molecules are made up of straight chain carbon atoms or branch chain e.g.

Butane (a straight chain compound)

2 methyl butane (a branched chain compound)

In cyclic compounds, the end carbon atoms of an open aliphatic chain can also join together to form a closed system or ring e.g.

Cyclopropane

AROMATIC COMPOUNDS

Aromatic compounds are Benzene or derivative of benzene (that is compounds whose structures are based on the structure of benzene)

Due to resonance exhibit by the structures of benzene, i.e.

• (ii)

The structure of benzene would be (i) or (ii)

Conventionally the structure of benzene is now a hexagon with a ring within it.

Examples of other derivatives of benzene: 

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