I found on the internet that propanol, propanone, propanoic acid and methyl ethanoate where all completely soluble in water at room temperature. (23 degrees Celsius) But I found that propanal was, comparatively, was not completely soluble in water (Wikipedia said it was 20g/100ml). I was wondering why it was not completely soluble like all the others as small aldehydes can interact with hydrogen bonds and dipole-dipole forces with water (like all the others). Is there some other intermolecular force that influences solubility that I'm missing?
They're all on the verge of miscibility, methyl ethanoate (methyl acetate) is in fact not miscible according to wikipedia (soluble to 25%).
The acid is the most polar of all the C3 compounds you name. Butyric acid (C4) is also miscible with water, but valeric acid (c5) already not.
n-butanol is already rather badly soluble (8g in 100ml) in water. Same with butanone, etc.
Compared to the ketone, the aldehyde has a longer unpolar part, that is overall less influenced by the polar carbonyl bond. Both are clearly, i think, the least polar of the group, and so the aldehyde just drops beneath the line.
No mystery here. ;-)