Why does hydrogen bonding occur in salicylic acid, and yet this acid is not particularly water-soluble?
1 Answer
Because water solubility is not a prerequisite for hydrogen bonding.
Explanation:
Two intermolecular interactions operate in salicylic acid, (i) dispersion forces which increase with the length of the molecule, and (ii) hydrogen bonding, which would occur between the carboxylate heads of 2 molecules. In small molecules such as water and hydrogen fluoride, hydrogen bonding tends to dominate as the intermolecular force. But............
But, as hydrocarbyl chain length grows in say alkanes, intermolecular interaction between the tails of each acid grows proportionally, and the boiling points of the alkanes increase with chain length.
For long-chain fatty acids, we would expect the carboxylic heads to aggregate, and yet there would be still be significant chain-chain interaction. The best macroscopic variable to interrogate this would possibly be the boiling point of the linear carboxylic acids, for which see this site. It is evident that as chain length grows the boiling point increases, and chain-chain interaction, is probably the determinant.
