4. Substitution reactions

A reaction in which an atom or a group of atoms in a given compound is replaced by other atom or group of atoms is called a substitution reaction.

Alkanes, the saturated hydrocarbons are chemically least reactive. Therefore they are also called paraffins (parum = little; affins = affinity, i.e., no affinity towards chemical changes). However they undergo some chemical changes under suitable conditions which are substitution reactions.

For example, methane (CH₄) reacts with chlorine in the presence of sunlight. Hydrogen atoms of CH₄ are replaced by chlorine atoms.

Many carbon compounds are invaluable to us. But here we study, the properties of Ethanol (Ethyl alcohol) and Ethanoic acid (Acetic acid) which are two very important carbon compounds.

Grains such as corn, wheat, barley are common sources for ethanol. Therefore, it is also called grain alcohol.

The process of conversion of starches and sugars to C2H5OH is called fermentation process.

Ethanol is a colourless liquid withcharacteristic sweet odour. Pure ethanol boils at 78.3 oC. Pure ethanol is called absolute (100 %) alcohol