[pretsnor]

Hello,



Hoe can i order these molecules by water solubility? I know that III and IV are ionic and therefore watersoluble: but how can i differentiate between III and IV?

For I and II, i reasoned that II is more soluble than I because it can donate 1 H bond. However (since i know the answer), this is not true. Why?

Thanks!

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[Babcock_Hall]

I would write down the various intermolecular forces that each compound is or is not capable of experiencing with water.

[pretsnor]

Allright. Correct me if i am wrong, please.

I: dipole-dipole, H - bond (acceptor)
II: dipole-dipole, H - bond (acceptor and donor)
III: hydration
IV: hydration

So III and IV are more soluble than I and II because they can be hydrated. Now what about the difference between I and II? Would II be more soluble because it can also donate H bonds? And what about the difference between III and IV. What do the double bonds have to do with solubility?

[Babcock_Hall]

For III and IV, I would say that they experience ion-dipole forces with water, as well as being able to donate and accept H-bond.  I reread your OP just now, and I may have misread it before.  One more thing to consider when comparing molecules, especially those with similar functional groups is that sometimes the ratios of polar to non polar groups on the molecule are very different.  For example acetic acid is highly water soluble, but as one increases the length of the carbon chain, the molecule becomes less water-soluble.   http://www.chemguide.co.uk/organicprops/acids/background.html