What causes differences in polarity between alcohol and ketone molecules?

[silversurf]

What is the relationship between polarity and hydrogen bonding? I have come across several problems saying that an alcohol is more polar than a ketone because of hydrogen bonding but I don't see the relationship between these two. Intuitively, I thought ketone would be more polar because it has a larger dipole but the explanation says that alcohol is more polar due to hydrogen bonding. In order to determine polarity I have been thinking about it in terms of electronegativity difference and dipole moment. But when we compare compounds like an ester vs a carboxylic acid structure, I haven't been able to tell which is more polar. The explanation only say that due to hydrogen bonding it's more polar but this seems like it came out of nowhere. Does anyone know what the relationship is?

 

[jbsteele]

The relationship between polarity and hydrogen bonding is that hydrogen bonding increases the polarity of molecules. This is because hydrogen bonds are stronger than other dipole-dipole interactions, and thus the molecules involved in hydrogen bonding become more polar. For example, alcohols are more polar than ketones because they can form hydrogen bonds, while ketones cannot. Hydrogen bonding also explains why esters and carboxylic acids are more polar than their corresponding alkanes, as carboxylic acids and esters can form hydrogen bonds, while alkanes cannot.