Question

Why are certain compounds called hydrocarbons? Write the general formula for the homologous series of alkanes, alkenes, and alkynes and also draw the structure of the first member of each series. Write the name of the reaction that converts alkenes into alkanes and also write a chemical equation to show the necessary conditions for the reaction to occur.

Answer 1

Step 1:

The organic compounds are made up of hydrogen and carbon atoms. Thus, these compounds are called hydrocarbons.

Hydrocarbons are further divided into two types:

1. Saturated hydrocarbons

2. Unsaturated hydrocarbons

Step 2:

A homologous series is a group of molecules that have comparable chemical characteristics and the same functional group, differing by $-{\mathrm{CH}}_2$ from one another.

The homologous series of alkanes, alkenes, and alkynes have the general formula ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+2},{\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}},{\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}-2}$.

Their structures can be written as: ${\mathrm{CH}}_4$, ${\mathrm{CH}}_2={\mathrm{CH}}_2$, $\mathrm{H}-\mathrm{C}\equiv \mathrm{C}-\mathrm{H}$.

Step 3:

An organic reaction in which two or more molecules combine to form a larger one( the adduct) is known as an addition reaction in organic chemistry.

The Addition reaction converts alkenes into alkynes.

The addition reaction of alkenes is written as;

${\mathrm{CH}}_2={\mathrm{CH}}_2+{\mathrm{H}}_2\stackrel{\mathrm{Ni},\mathrm{heat}}{\to }{\mathrm{CH}}_3-{\mathrm{CH}}_3$

The necessary conditions for the reaction to occur.is the use of Nickel ($\mathrm{Ni}$) or Platinum ($\mathrm{Pt}$) catalyst.

The presence of heat is the necessary condition to proceed the above reaction.