SummaryIt was found that during the hydrogenation of octadecenoic acids, migration of the double bonds takes place equally in each direction. The positional isomers that are formed are composed of the 1∶2 equilibrium mixture ofcis andtrans. A partial hydrogenation‐dehydrogenation theory may be applied to explain the simultaneous formation of both positional and geometrical isomers.

SummaryThe isomerization that takes place during the catalytic hydrogenation of linoleic acid and methyl linoleate producescis andtrans 9, 10, 11, and 12 monoenes. The double bond at the 12 position appears to hydrogenate slightly faster than that in the 9 position. More octadecenoic acids with double bonds at the 10 or 11 positions are produced during a selective (high temperature, low pressure) hydrogenation than during a non‐selective process.Although the degree of selectivity of the hydrogenation is determined by the amount of isomerization of the original pentadiene system to a conjugated diene, only part of the methylene‐interrupted diene goes through this type of isomerization even during a highly selective hydrogenation.The half hydrogenation‐dehydrogenation reaction mechanism is applied to explain the simultaneous positional and geometrical isomerizations.

Summary Ozonolysis and chromatographic procedures as a method for determining the position of double bonds in olefinic acids are not entirely satisfactory. Ozonolysis is seriously limited because of the secondary reactions undergone by the ozonide. Chromatographic resolution of the decomposed ozonides of oleic acid yields the expected pelargonic and azelaic acids but also yields fractions that indicate double bonds which do not exist. Fractions corresponding to pimelic, sebacic, caprylic, suberic, and capric acids appeared. The “pimelic acid” fraction resulted from the reaction of ozone with an oxidizable or hydrolyzable solvent such as acetone, methanol, or tetrachloromethane. The “sebacic” and “caprylic acid” fractions were incompletely decomposed ozonide. The suberic and capric acid fractions however were real and are believed to have resulted from 8‐octadecenoic acid present in the oleic acid in amounts too small to be detected by the methods used to establish its purity.

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