The literature on identification of long-chain fatty acids, esters, and alcohols is relatively sparse. In addition, numerous difficulties arise in attempting to utilize chemical derivatives for identification purposes. Urea complexes have been prepared in high yield from 42 long-chain compounds, consisting of fatty acids, methyl and vinyl esters, alcohols, a mono-and diglyceride, and a vinyl ether. These include several cis-trans pairs (oleic-elaidic acids, methyl oleate-elaidate, oleyl-elaidyl alcohols) and some long-chain compounds with oxygen-containing functional groups (oxirane, hydroxyl, keto) in the chain. With a few exceptions, the dissociation temperature of each of these complexes has been determined. A t this temperature, the complex dissociates and the transparent hexagonal crystals are converted to an opaque mass of microcrystals. The dissociation temperature, which is the temperature at which HE usual schemes for the positive identification of organic T compounds include the preparation of suitable solid chemical derivatives (3, 7 , If, 20). The literature on identification of the long-chain fatty acids, esters, and alcohols reveals numerous difficulties in attempting to utilize derivatives for this purpose. For example, although many derivatives of long-chain fatty acids have been reported, the melting points of epecific derivatives (amide, pbromoanilide, p-phenylphenacyl ester, etc.) of many members of this homologous series are usually too close together to permit positive identification. Derivatives of long-chain alcohols suffer from the same drawback and, in addition, the literature on them is relatively sparse. Esters are usually characterized by hydiolysis, followed by separation-frequently tedious-and identification of the acid and alcohol portions, or they may be converted directly to certain derivatives (hydroxamic acids, amides, etc.) which permit identification of the acid moiety. In either case, the ester is destroyed and, of course, nonrecoverable.