Question

The next higher homolog of ethanol is ______.

• A. Propanol
• B. Methanol
• C. Butanol
• D. Pentanol

Answer 1

The correct option is A

Propanol

Explanation for the correct option

(A)

• A homologous series is a series of carbon compounds that possess the same functional group and have similar chemical characteristics. The series' members can either be branched or unbranched, but differ by $-{\mathrm{CH}}_2$ group.
• The molecular formula for ethanol is ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}$. The structure of ethanol is ${\mathrm{CH}}_3-{\mathrm{CH}}_2-\mathrm{OH}$.
• To get the next homolog, add $-{\mathrm{CH}}_2$ group in the formula of ethanol. So, the next higher homolog of ethanol becomes ${\mathrm{C}}_3{\mathrm{H}}_7\mathrm{OH}$ and the structure will be ${\mathrm{CH}}_3-{\mathrm{CH}}_2-{\mathrm{CH}}_2-\mathrm{OH}$, and the name of the compound is propanol.
• Thus, The next higher homolog of ethanol is propanol.

Explanation for the incorrect options:

(B) Methanol $\left({\mathrm{CH}}_3\mathrm{OH}\right)$ is the preceding homolog of ethanol $\left({\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}\right)$.

(C) Butanol $\left({\mathrm{C}}_4{\mathrm{H}}_9\mathrm{OH}\right)$ is not the next higher homolog of ethanol. It is the next higher homolog of propanol $\left({\mathrm{C}}_3{\mathrm{H}}_7\mathrm{OH}\right)$.

(D) Pentanol $\left({\mathrm{C}}_5{\mathrm{H}}_{11}\mathrm{OH}\right)$ is not the next higher homolog of ethanol. It is the next higher homolog of butanol $\left({\mathrm{C}}_4{\mathrm{H}}_9\mathrm{OH}\right)$.

Hence, the correct option is (A). The next higher homolog of ethanol is propanol.