Question

Write the name and general formula of a chain of hydrocarbons in which an addition reaction with hydrogen can take place. Stating the essential conditions required for an addition reaction to occur, write the chemical equation giving the name of the reactant and the product of such a reaction.

Answer 1

Hint: To answer this question, it is very important for us to know the general formula of the hydrocarbons, in which an addition reaction with hydrogen can take place. Then, for writing the essential conditions, we need to have an idea about the reactions. Once we know the occurrence of the reactions, we know the conditions favouring the addition reaction.

Step by step answer:
Addition reactions with hydrogen take place in unsaturated hydrocarbons which are Alkenes and Alkynes. The general formula for Alkenes and Alkynes are following:
Alkenes : ${{\text{C}}_{\text{n}}}{{\text{H}}_{\text{2n}}}$
Alkynes : ${{\text{C}}_{\text{n}}}{{\text{H}}_{\text{2n}-\text{2}}}$
The essential conditions which are required for an addition reaction to occur are as follows:
1. The presence of multiple bonds (double and triple bonds) between carbon atoms in the chain of a hydrocarbon.
2. The addition of hydrogen should be carried out in the presence of a catalyst such as Nickel and Platinum.
Here is the chemical equation which would explain the mentioned process:
$\text{C}{{\text{H}}_{\text{2}}}\text{= C}{{\text{H}}_{\text{2}}}\text{ + }{{\text{H}}_{\text{2 }\!\!~\!\!\text{ }}}\text{ }\xrightarrow{\text{Ni or Pt}}\text{ }\!\!~\!\!\text{ C}{{\text{H}}_{\text{3}}}\text{ - C}{{\text{H}}_{\text{3}}}$
In the reaction which is mentioned above, the reactant is Ethene and the product formed is Ethane. The reaction which is mentioned, also requires a lot of heat for the occurrence.

Additional Information:
Electrons of benzene rings are delocalised throughout the molecule, which makes the molecule very stable. The addition reaction would result in breaking of these delocalizations, which means the stability of the molecule will be destroyed. This is the reason why Benzene does not undergo addition reactions.

Note: There are two main types of polar addition reactions. They are electrophilic addition and nucleophilic addition. Two non – polar addition reactions also exist, they are called free radical addition and cycloadditions. Addition reactions are also encountered in polymerizations and called addition polymerizations.