In the presence of an olefin, CF2Br. radicals add to the double bond with a constant rate that depends only modestly on the olefin nature (1-hexene, 2.3-dimethyl-2-butene and ethylacrylate). However, the fate of the radical adduct depends on the nature of the olefin and controls the nature of the main electrolysis product(s). For 1-hexene, the radical adduct abstract a Br-atom from the parent CF2Br2. This triggers a rapid radical chain reaction, which results overall in the addition of CF2Br2 across the double bond. For ethylacrylate, the radical adduct ads to the parent olefin, which initiate oligomerisation. For 2.3-dimethyl-2-butene, the radical adduct undergoes dismutation. Cyclopropanation is observed only with 2.3- dimethyl-2-butene and corresponds to a fast trapping of the carbene CF2 before it may react with DMF. For the two other olefins, reaction of CF2 with DMF is preferred.