Organic Compounds
In organic compounds, the weight percent of hydrocarbon chain often determines the compound's miscibility with water. For example, among the alcohols, ethanol has two carbon atoms and is miscible with water, whereas octanol with a C8H17 substituent is not. Octanol's immiscibility leads it to be used as a standard for partition equilibria. This is also the case with lipids; the very long carbon chains of lipids cause them almost always to be immiscible with water. Analogous situations occur for other functional groups. Acetic acid (CH3COOH) is miscible with water, whereas valeric acid (C4H9COOH) is not. Simple aldehydes and ketones tend to be miscible with water, because a hydrogen bond can form between the hydrogen atom of a water molecule and the unbonded (lone) pair of electrons on the carbonyl oxygen atom.
Read more about this topic: Miscibility
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