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.

 

[LudusRex]

I would approach this question by first understanding the concept of hydrogen bonding. Hydrogen bonding is a type of intermolecular force that occurs between molecules containing hydrogen atoms bonded to highly electronegative atoms such as oxygen, nitrogen, or fluorine. In the case of water, each molecule can form up to four hydrogen bonds with other water molecules due to its unique bent structure and the presence of two hydrogen atoms bonded to an oxygen atom.

To find the number of hydrogen bonds between molecules, we need to first identify the molecules that can form hydrogen bonds. In the case of isopropyl alcohol, it has one OH group, which means it can form hydrogen bonds with other molecules that have a hydrogen atom bonded to an electronegative atom. However, unlike water, isopropyl alcohol has a linear structure and only one hydrogen atom bonded to the oxygen atom. This means that it can only form one hydrogen bond with another molecule.

To confirm this, we can also look at the physical properties of water and isopropyl alcohol. Water has a higher boiling point and surface tension compared to isopropyl alcohol, which can be attributed to the stronger intermolecular forces (hydrogen bonds) present in water. This further supports the fact that water can form more hydrogen bonds compared to isopropyl alcohol.

In conclusion, based on the structure and physical properties of isopropyl alcohol, it can be determined that it can only form one hydrogen bond with other molecules. However, further research and experimentation may be needed to confirm this and determine the exact number of hydrogen bonds in a specific system.