Question

How would we compare and rationalize the normal boiling points of ethylene glycol versus that of acetic acid?

Answer 1

We would normally predict that an acid has a higher boiling point than an alcohol; however, ethylene glycol is a DIOL.

Explanation:

As a chemist, as a physical scientist, you should always look at the evidence, in other words, consider and rationalize the data. No one expects you to know offhand the boiling point of any liquid (other than water, and ethanol, and methanol). I knew the boiling point of acetic acid, `119` `""^@C`; I did not know the boiling point of ethylene glycol, which is `197.3` `""^@C`.

Now, should you compare these boiling points to the corresponding alkanes, clearly, you would account for the disparity in terms of the presence or absence of hydrogen bonding. However, ethylene glycol has 2 groups available for INTERMOLECULAR hydrogen bonding, whereas acetic acid, only has the one group available. Because there is greater opportunity for intermolecular bonding in the case of the diol, the force between molecules, its boiling point is elevated.

A better comparison for ethylene glycol MIGHT be `HO(O=)C-C(=O)OH`. It is a solid that sublimes at 190 °C.