Among the saturated monocarboxylic acids, formic acid, acetic acid, and propionic acid have a strong sour taste and irritation. It contains 4~9 C atoms and has a putrid odor and is an oily liquid. It contains more than 10 C's as a paraffin-like solid, with very low volatility and no odor.

This is due to the presence of hydrogen bonds between the molecules of formic acid. According to methods such as electron diffraction, lower acids exist in the form of dimers even in vapor due to the presence of hydrogen bonds. The intermolecular hydrogen bond bond of formic acid is 30KJ/mol, while the intermolecular hydrogen bond of ethanol is 25KJ/mol.

X-ray studies of long-chain fatty acids have proved that the C chains in these molecules are arranged in a zigzag shape, and the two intermolecular carboxyl groups are associated with hydrogen bonds, and the associated bimolecules are arranged regularly layer by layer, and in the middle of each layer is a carboxyl group that is associated with each other, and the gravitational attraction is very strong, and the layers are adjacent to each other with weak gravitational alchemies, which are easy to slide between each other, which is also the reason why higher fatty acids have lubricity.