Question

$C{ H }_{ 3 }-C{ H }_{ 2 }-C{ H }_{ 2 }-CH=C{ H }_{ 2 }$ is an unsaturated hydrocarbon.
A. To which homologous series this compound is a member?
B. Write the general formula representing this homologous series.
C. Write the structural formula successive to this compound.

Answer 1

Hint: Homologous series of compounds is referred to as the series of compounds that have the same general formula but differ from adjacent members by $"-C{H}_{2}-"$ group. They are determined by the hydrocarbon chain.

Complete step by step answer:
The homologous group of compounds are like alkanes, alkenes, alkynes, etc. The alkanes only have carbon atoms that are attached to the other carbon atoms through single bonds. In alkenes, the carbon atoms are connected through at least one double bond and the rest with single bonds. In alkynes, the carbon atoms are connected through at least one triple bond and the rest are single bonds.

A. The given compound $C{ H }_{ 3 }-C{ H }_{ 2 }-C{ H }_{ 2 }-CH=C{ H }_{ 2 }$, there is one double bond between two carbon atoms and the rest are single bonds. All the compounds belonging to this homologous series have the same general formula and end with the suffix -ene. The first member of this series is ethane that has the chemical formula ${H}_{2}C=C{H}_{2}$. Therefore, from the definition, this compound belongs to the alkene homologous series of compounds.

B. The general formula of alkenes is given as ${C}_{n}{H}_{2n}$ where n is the no. of carbon atoms in the compound. As we can see that the given compound has 5 carbon atoms, 10 hydrogen atoms and one double bond. Therefore, the chemical formula of this compound is ${C}_{2}{H}_{10}$ which satisfies the general formula.

C. As we saw earlier, this compound contains 5 carbon atoms and the successor of this homologous series has an additional $"-C{H}_{2}-"$. Thus, the successor of this compound will have an additional $"-C{H}_{2}-"$. Therefore, the formula would become

$C{ H }_{ 3 }-C{ H }_{ 2 }-C{ H }_{ 2 }-C{ H }_{ 2 }-CH=C{ H }_{ 2 }$. 

The structural formula is given as follows.

Note: The double bond can be shifted to different positions in a carbon atom. Those different structures are known as isomers. These are the compounds which have the same molecular formula but differ in spatial arrangements.