# Why does glycerol have a higher normal boiling than triacetin, HC{OC(=O)CH_3}_3, even though the latter molecule has a higher molecular mass?

##### 1 Answer
Nov 24, 2016

What intermolecular force exists in the triol, $\text{glycerol}$, that does not exist in the ester?

#### Explanation:

The answer is $\text{hydrogen bonding}$. $\text{Glycerol}$, ${H}_{2} C \left(O H\right) C H \left(O H\right) C {H}_{2} \left(O H\right)$ is extremely viscous, and is quite involatile, ${\text{b.p = 290}}^{\circ} C$. Clearly, the degree of intermolecular force, i.e. the force BETWEEN molecules, is substantial. And that intermolecular force is likely hydrogen-bonding, which is also repsonsible for the elevated boiling points of $O {H}_{2}$, $N {H}_{3}$, and $H F$, much smaller molecules, but also where hydrogen-bonding operates decisively.

On the other hand, its triester with 3 equiv acetic acid (which I think is commonly called $\text{triacetin}$), removes this intermolecular force by eliminating the alcoholic function. The result?

The normal boiling point of triacetin is ${\text{b.p = 259 }}^{\circ} C$, substantially lower than glycerol, even though glycerol has LESS dispersion forces in that it is a smaller molecule. Hydrogen bonding WINS as an intermolecular force.