Question

Write the molecular formula of lower and higher homologues of ${\mathrm{C}}_4{\mathrm{H}}_{10}$.

Answer 1

Step 1:

Homologous series of compound lies in the same family and the molecular formula is different by one ${\mathrm{CH}}_2$ unit.

Butane $\left({\mathrm{C}}_4{\mathrm{H}}_{10}\right)$ is a saturated compound.

If a compound adds or subtracts by one unit of ${\mathrm{CH}}_2$ from that compound then it is a homologous compound.

Step 2:

The higher homologous of ethane compound is by adding one unit of ${\mathrm{CH}}_2$

$$\begin{gathered} {\mathrm{C}}_4{\mathrm{H}}_{10}+{\mathrm{CH}}_2\to {\mathrm{C}}_5{\mathrm{H}}_{12} \\ \mathrm{Butane}\mathrm{pentane} \\ (\mathrm{lower}\mathrm{homologue})(\mathrm{higher}\mathrm{homologue}) \end{gathered}$$

The lower homologous of ethane compound is by subtracting one unit of ${\mathrm{CH}}_2$

$$\begin{gathered} {\mathrm{C}}_4{\mathrm{H}}_{10}-{\mathrm{CH}}_2\to {\mathrm{C}}_3{\mathrm{H}}_8 \\ \mathrm{Butane}\mathrm{Propane} \\ (\mathrm{higher}\mathrm{homologue})(\mathrm{lower}\mathrm{homologue}) \end{gathered}$$

Final answer:

Hence, the higher homologous of ${\mathrm{C}}_4{\mathrm{H}}_{10}$ is Pentane (${\mathrm{C}}_5{\mathrm{H}}_{12}$) and the lower homologous of ${\mathrm{C}}_4{\mathrm{H}}_{10}$ is Propane (${\mathrm{C}}_3{\mathrm{H}}_8$).