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Sorry if this is an obvious answer. I tried rewording this question every way I could, but search engines came up with nothing- they all skirted around this exact question.

Why do certain compounds, such as fatty acid or Vitamin A, dissolve in oil?

Polar substances can dissolve in water because water molecules are polar and literally pick apart the [polar] molecules in the solute by attracting to them. However, oil is nonpolar and has no such ability.

How, then, does it make certain compounds dissolve? Is there some other bond it can form with certain compounds?

On a second question, I read something about London dispersion and Van der Waals forces being the main force of attraction between oil solvents and solutes that can dissolve in oil. If this is the case, that means the electrons in orbit around the solute's molecules shift around and form temporary dipoles with each other.

But what makes it so that some solutes can only dissolve in oil-- and not water [molecules], which are polar, and could also interact with these temporary dipoles?

edit: A comment said that this not energetically preferable. So I think the second question can be considered answered.

Thanks!

Anise
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  • Water molecules create mutual relatively strong hydrogen bonds what releases bond energy. Weak bonding with a nonpolar molecule is not energetically preferred. – Poutnik Oct 26 '20 at 14:57
  • Indeed is the way things are presented. If I get it, you see an active mechanism for the solubilzation of salt and polar molecules in water / polar solvents but the counterpart for apolar stuff seems to be missing. Indeed, there are other forces at play - still electrostatic in nature although transient. Also entropy favours dissolution. Remember the "rule" like dissolve like. – Alchimista Oct 26 '20 at 16:00
  • @Poutnik Thanks. I think that answers the second question. I'm not sure if the question should be deleted now? – Anise Oct 26 '20 at 19:55
  • No, keep it. Questions and answers are aimed to have permanent value, if others have similar questions in future. – Poutnik Oct 26 '20 at 19:57
  • @Alchimista Would the main cause of a solute's dissolution in oils be the Van der Waals forces, then? Or do the other forces you mention play more of a role? Edit: Yes, the counterpart for the apolar stuff is missing because I know very little about how apolar solvents and solutes interact. – Anise Oct 26 '20 at 20:00
  • @Anise yes let us call them VdW. Their treatment in details is not in the current scope. Look at the problem in light of Maurice answer (ie if something stay togheter there are forces keeping it as an ensemble. While it is easy to see them in ionic crystals or polar compounds, is more subtle to analyse them in apolar molecular lattices. Still they are el.magn. in nature. Also as Poutnik said, there is alway an energetic balance. – Alchimista Oct 26 '20 at 20:33

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I propose a logical approach, to explain the rule "the like dissolve like". Why don't we admit that all liquids should be able to mix, exactly like gases may be mixed in all proportion ? This is the case for non polar molecules, like oils. And if two liquids don't mix, this is due to the existence of attracting forces between molecules A (hydrogen bonds for exemple), and that mixing them with another stuff B may destroy too many of these bonds. If the mixing operation A + B creates about as many new bonds as those broken during the mixing, the liquids A and B may be mixed. This is the case in the mixture water - ethanol. If the mixing operation A+B does not create enough new bonds between molecules A and B, like water and oil, Nature refuses to break the bonds between A molecules without any counterpart, and prevents the A molecules (water) to be separated from one another in order to accept B molecules, and A and B are not miscible.

Maurice
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  • Thank you. Your answer puts a whole new perspective on my current understanding of how bonds are made. Out of curiosity... is it possible for the mixing operation A + B to create more bonds than those broken? If so, what will happen? – Anise Oct 26 '20 at 20:14
  • @Anise. If the mixing operation creates more bonds than those broken, this means that a new chemical species has been obtained containing A and B. – Maurice Oct 26 '20 at 21:04