Question

Write the IUPAC name and structural formula of the first four members of the alcohol homologous series.

Answer 1

Hint: A series of members of the same family in an increasing order of their molecular weights is known as a homologous series. The two consecutive members of the homologous series differ by $ - {\text{C}}{{\text{H}}_2}$. The alcoholic functional group is hydroxyl $\left( { - {\text{OH}}} \right)$.

Complete step by step solution:
First we will determine the first four members of the alcohol homologous series. The two consecutive members of the homologous series differ by $ - {\text{C}}{{\text{H}}_2}$. The alcoholic functional group is hydroxyl $\left( { - {\text{OH}}} \right)$.
Thus, the first member of the alcohol homologous series is methyl alcohol, the second is ethyl alcohol, the third member is propyl alcohol and the fourth member is butyl alcohol.
The formula that shows the arrangement of atoms in a molecule of a compound is known as a structural formula.
The molecular formula for first four members of the alcohol homologous series are as follows:
Methyl alcohol - ${\text{C}}{{\text{H}}_{\text{3}}} - {\text{OH}}$
Ethyl alcohol - ${\text{C}}{{\text{H}}_{\text{3}}} - {\text{C}}{{\text{H}}_2} - {\text{OH}}$
Propyl alcohol - ${\text{C}}{{\text{H}}_{\text{3}}} - {\text{C}}{{\text{H}}_2} - {\text{C}}{{\text{H}}_2} - {\text{OH}}$
Butyl alcohol - ${\text{C}}{{\text{H}}_{\text{3}}} - {\text{C}}{{\text{H}}_2} - {\text{C}}{{\text{H}}_2} - {\text{C}}{{\text{H}}_2} - {\text{OH}}$
The method of naming organic compounds is known as the IUPAC nomenclature. The rules for writing IUPAC name of alkenes are as follows:
Select the longest continuous chain of carbon atoms containing hydroxyl functional groups in the structure of the molecule.
Count the number of carbon atoms in the chain. This is the parent alkane.
The name of alkene is written by replacing the suffix ‘ane’ in the parent alkane by ‘ol’.
Thus,
The IUPAC name for methyl alcohol ${\text{C}}{{\text{H}}_{\text{3}}} - {\text{OH}}$ is methanol.
The IUPAC name for ethyl alcohol ${\text{C}}{{\text{H}}_{\text{3}}} - {\text{C}}{{\text{H}}_2} - {\text{OH}}$ is ethanol.
The IUPAC name for propyl alcohol ${\text{C}}{{\text{H}}_{\text{3}}} - {\text{C}}{{\text{H}}_2} - {\text{C}}{{\text{H}}_2} - {\text{OH}}$ is propanol.
The IUPAC name for butyl alcohol ${\text{C}}{{\text{H}}_{\text{3}}} - {\text{C}}{{\text{H}}_2} - {\text{C}}{{\text{H}}_2} - {\text{C}}{{\text{H}}_2} - {\text{OH}}$ is butanol.

Note:
The functional group decides the activity of a compound. The functional group of alcohol is $ - {\text{OH}}$. The homologous series shows variation in properties in an ascending or descending order.