# What intermolecular forces present in ethanol?

May 7, 2018

The normal boiling point of ethanol is $+ 78$ ""^@C.

#### Explanation:

That of ethane is $- 89$ ""^@C; that of propane is $- 42$ ""^@C; that of butane is $- 1$ ""^@C; that of dimethyl ether is $- 24$ ""^@C;

What has ethanol got that the hydrocarbons and the ether ain't got? Why should this lead to potent intermolecular force? And it is the same intermolecular force that operates in water, and ammonia, and hydrogen fluoride, the which solvents ALSO have anomalously high normal boiling points.

The answer of course is intermolecular hydrogen bonding. Hydrogen is bound to a strongly electronegative atom, here oxygen, and it polarizes electron density towards itself to give the following dipole...

$\stackrel{{\text{^+delta)H-stackrel(}}^{-} \delta}{O} - C {H}_{2} C {H}_{3}$

In bulk solution the dipoles line up, and this constitutes a quite considerable intermolecular force of attraction that elevates the boiling point. And the result...compare the normal boiling point of ethanol, $78$ ""^@C, versus ethane, $- 89$ ""^@C. Is the difference in volatility consistent with our argument?