Of the two isomers maleic and fumaric acids which one is more soluble in a polar solvent like water? why
The answer is here near the top. And it follows through from my educated guess on the dipole moment.
I found some data.
maleic form is soluble at 78.8 g/100 cc water. Fumaric solubility is 0.7 g/100 cc water. Again, that is consistent with the best guess about dipole moment.
To determine which isomer, maleic or fumaric acid, is more soluble in a polar solvent like water, we need to consider their structural differences.
Both maleic and fumaric acids are dicarboxylic acids with the same molecular formula, C4H4O4, but they have different arrangements of their carboxylic acid functional groups.
Maleic acid consists of two carboxylic acid groups attached to the same carbon atom on the same side of the molecule. This arrangement creates a cis configuration.
Fumaric acid, on the other hand, has the carboxylic acid groups attached to different carbon atoms on opposite sides of the molecule, giving it a trans configuration.
Now, the cis configuration of maleic acid causes the molecule to have a higher dipole moment compared to fumaric acid. A higher dipole moment indicates a greater polarity in the molecule.
Since water is a polar solvent, it interacts more favorably with polar molecules through hydrogen bonding. Therefore, the greater the polarity of the molecule, the more soluble it is in water.
Due to the higher dipole moment resulting from its cis configuration, maleic acid is more soluble in water compared to fumaric acid, which has a trans configuration.