Question

The general formula which represents the homologous series of alkanols is

• A. $C_n{H}_{2n}{O}_2$
• B. $C_n{H}_{2n}O$
• C. $C_n{H}_{2n+1}O$
• D. $C_n{H}_{2n+2}O$

Answer 1

The correct option is D

${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+2}\mathrm{O}$

Explanation for the correct option

(D)

• Homologous series refers to a set of organic compounds that have similar structural properties but differ from adjacent members by the $-{\mathrm{CH}}_2$group.
• Alkanols are alkanes containing a hydroxyl group $\left(-\mathrm{OH}\right)$.
• The general formula of alkanes is ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+2}$. When one hydrogen atom is replaced by a hydroxyl group, it becomes alkanols.
• So, the general formula of alkanols is ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+1}\mathrm{OH}$ or ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+2}\mathrm{O}$.
• For example, ethanol $\left({\mathrm{C}}_2{\mathrm{H}}_6\mathrm{O}\right)$, propanol $\left({\mathrm{C}}_3{\mathrm{H}}_8\mathrm{O}\right)$, butanol $\left({\mathrm{C}}_4{\mathrm{H}}_{10}\mathrm{O}\right)$.

Explanation for the incorrect options

(A) ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}}{\mathrm{O}}_2$ is the general formula for an open chain of carboxylic acids or ester. For example, acetic acid $\left({\mathrm{CH}}_3\mathrm{COOH}\right)$

(B) ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}}\mathrm{O}$ is the general formula for aldehydes. For example, acetaldehyde $\left({\mathrm{CH}}_3\mathrm{CHO}\right)$

(C) ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+1}\mathrm{O}$ is not the general formula for the homologous series of alkanols.

Hence, option (D) is correct. The general formula for alkanols is ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+2}\mathrm{O}$.