Organic Chemistry - Caffeine Lab

[Suzy Tran]

Hello I have a few problems with figuring out intermolecular forces between interactions of caffeine and water/ caffeine and methylene chloride (DCM) for my lab. Here are the questions:

 

1. Identify and discuss two different structural features that would account for solubility in methylene chloride (hint: think intermolecular forces).
2. Identify (circle on your structure) and discuss two different structural features that would account for solubility in water (hint: think intermolecular forces).

I attempted the problems and think that London dispersion forces are in between the caffeine and DCM interactions but not in the caffeine & water interactions because caffeine and water are already polar. Also, another interaction between caffeine & DCM is dipole-induced-dipole because DCM is nonpolar and is being induced by a polar compound (caffeine). For caffeine & water, I think that there is hydrogen bonding involved because the oxygens on caffeine (a part of the amide group) can interact with water for hydrogen bonding. However, I'm unsure with my answers and not sure what structural features go along with what I said especially for the interactions between caffeine and DCM.

 

Thank you for those that take the time to help!

[BabcockHall]

All molecules undergo London forces, but they are not always the dominant interaction. Does dichloromethane have a dipole moment? Besides H-bonding, are there other interactions between water and caffeine?

Edited September 29, 2015 by BabcockHall

[Suzy Tran]

According to my TA, there are London Dispersion but I'm unsure if both of caffeine/DCM and caffeine/water interactions go through them as the dominant interaction. In DCM, I'm pretty sure there are dipole moment between Carbon and Chlorine. One chlorine is pointing up and the other one is pulling more downwards, these two dipole moments doesn't cancel each other out so it makes DCM kind of/ partially polar. For the other interactions between water and caffeine, well there's definitely london dispersion and hydrogen bonding, I'm not sure what else so I guess those are the two for water/caffeine interactions. I guess now I'm not 100% sure about caffeine/DCM interactions. Thanks BabcockHall.

Edited September 29, 2015 by Suzy Tran

[BabcockHall]

I agree that DCM has a permanent dipole moment. Water obviously has a dipole moment. What about caffeine? If it has a dipole moment, then that would produce dipole-dipole interactions in either case.

[Suzy Tran]

Oh I see, caffeine does have a dipole moment I think I'm not fully understanding what dipole-induced-dipole is. Then the caffeine/DCM interactions would be dipole-dipole since both are dipole?

[BabcockHall]

If DCM encountered a non polar molecule such as hexane, they could interact via dipole, induced-dipole forces.