Chapter 8, Problem 82A

Interpretation Introduction

Interpretation: The reason for the difference in the boiling point of ethyl alcohol and dimethyl ether needs to be explained.

Concept Introduction: A hydrogen bond is formed when a hydrogen atom in a molecule bonded with an electronegative atom makes a bond with an electronegative atom of the same or different molecule bonded with hydrogen atom.

Explanation of Solution

The chemical formula for ethyl alcohol and dimethyl ether is ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{OH}$ and ${\text{CH}}_{\text{3}}{\text{OCH}}_{\text{3}}$ respectively. Here, both molecules have the same number of carbon, hydrogen, and oxygen atoms. The boiling point of ethyl alcohol is ${78}^{\text{o}}\text{C}$ , but the boiling point of dimethyl ether is $-25{}^{\text{o}}\text{C}$ . The difference in boiling points is due to the difference in the bonding between atoms.

The structures for ethyl alcohol and dimethyl ether are as follows:

  

In ethyl alcohol, the hydrogen atom is attached to electronegative oxygen atoms thus, intermolecular hydrogen bonding is possible. Since no hydrogen atom is directly bonded to the oxygen atom in dimethyl ether, hydrogen bonding is not possible. Due to the presence of hydrogen bonding between molecules of ethyl alcohol, it has a higher boiling point than dimethyl ether.