How do you find the number of hydrogen bonds between molecules?

[MeMoses]

Hey, I'm wondering how you figure out the number of hydrogen bonds acting between molecules. I know each water molecule supposedly makes 4 hydrogen bonds with other water molecules through my reading, but I want to know how many for isopropyl alcohol, which has only one OH group. I know its less than water based on the properties of the two, but that's it. I think it may be either 1 or 3 but I am not sure how to figure this out. Any help would be appreciated.

 

[Jorriss]

If it were three, what hydrogens on isopropyl alcohol would be involved in hydrogen bonding?

 

[MeMoses]

Hydrongens in the OH group of other molecules would be used. You could have two H from other molecules bond to the O of the original molecule and then the H (of the original molecule) bonds to the O of another. If that is allowed

 

[Yanick]

If its H-bonding with only one species present (IE neat EtOH) just look at the molecule and find the H-bond donor(s) and H-bond acceptor(s). It can get much more complicated if there are more than one species present (IE such as a solution or a mixture etc) because other effects, such as sterics and such, may play a role as to what H-bond with what

So for EtOH, we have CH₃CH₂OH. One H-bond donor, but two lone pairs on the Oxygen can accept 2 H-bonds (from two other molecules of EtOH). So 1 molecule of EtOH can H-bond to three other EtOH molecules.