Reactions of perfluoro(2-methyl-2-pentene) (1), the thermodynamic dimer of hexafluoropropene (HFP), are sometimes impossible to explain without invoking isomerization to terminally unsaturated perfluoro(2-methyl-1-pentene) (2) [1], [2] and [3]. One well-known incidence of such isomerization is evident in the structure of thermodynamic HFP trimer. It contains a normal propyl group (instead of isopropyl), which is derived from the isomeric dimer 2 with the terminal double bond [4] ( ...