Raman spectra of (1) propionic acid, (2) formic acid, (3) benzoic acid and (4) cinnamic acid have been studied using the pure acids in the liquid or molten condition and solutions in various solvents, benzene (non-associating), water, ether dioxan, acetal, etc. (associating). The first closely resembles acetic acid both of them indicating the existence of ring dimers, open dimers and monomers, the last two forms being present to a very small extent in the free state and in increasing quantities (in association with solvents) in solution in associating liquids. The state of the molecules in formic acid seems to be more complex due probably to the capacity of H of the C−H group to form hydrogen bonds. There are 2 broad C=O lines equally strong in the pure liquid at 1670 and 1715 cm.−1; the former diminishes and the latter increases in solutions with associating solvents. The narrowing of the band at 190 cm.−1 is another characteristic. It seems to be possible that in this acid no molecular type having unco-ordinated C=O exists. Benzoic and cinnamic acids form a different type. The molten acids and benzene solutions give only one C=O line corresponding to ring dimers and in fairly dilute solutions in ethers monomer-associates alone containing unco-ordinated C=O groups exist. Thus they do not give indications of the intermediate open type of dimers.