Question

Which of the following has the highest boiling point? Please provide an explanation on how to solve this!

a. CH₃OH                b. CH₃Cl                  c. CH₃SH                 d. CH₃CH₃                       e. CH₃F

Answer 1

Methanol, CH₃OH, will have the highest boiling point. This is due to intermolecular hydrogen bonding between the O atom of the hydroxyl group of one CH₃OH molecule with the H atom of the –OH group of the next molecule as shown below:

                                                               O-H…..O

Due to this hydrogen bonding between adjacent methanol molecules, a large number of methanol molecules are aggregated to form a giant conglomerate. A large amount of heat energy is required to break the intermolecular hydrogen bonds and hence CH₃OH will have the highest boiling point. The hydrogen bond is possibly only in case of CH₃OH because of the high electronegativity and appropriate size of O atom.

In CH₃-F, the F atom is more electronegative than O atom, but the size of F atom is extremely small to participate in hydrogen bonding; hence no hydrogen bonding is seen in CH₃F.