Vapor pressure of ethanoic acid vs. ethanol

[i_love_science]

Homework Statement

Ethanoic acid (CH3COOH) has a much lower vapor pressure than ethanol (CH3CH2OH). What is the most reasonable explanation?

A) The polarizability of 2 oxygen atoms increases London forces of attraction in ethanoic acid compared with ethanol.
B) Hydrogen bonding in ethanoic acid is the strongest attractive force and is mainly responsible for the observed data.
C) Ethanol has a -OH group and can hydrogen bond; therefore the London forces must cause the effect.
D) Both ethanol and ethanoic acid have an -OH, so the difference is the dipole of the 2nd oxygen that increases the attractive forces.

Relevant Equations

intermolecular forces

I think the answer is D because both molecules can hydrogen bond with their OH groups, but the C=O bond in ethanoic acid is polar and contributes to dipole-dipole interactions.

The solution says B is the correct answer, because ethanoic acid molecules strongly hydrogen bond so that most molecules are part of dimers. I don't really understand this, and why I'm wrong. Could anyone help me? Thanks.

 

[chemisttree]

Yes, B is correct. Arrange two molecules so that the OH group of one is close to the C=O group of the other, yin/yang fashion.