Do fluorine atoms attached to sp2-hybridized carbon atoms hinder electrophilic addition to the CC bond?

Interaction of mercuric trifluoroacetate with 2,3-difluorobicyclo[2.2.1]hepta-2,5-diene ( I ) in a non-polar medium leads to adduct IIa , formed as a result of exo—cis -addition of the salt to the FCCF bonds of two diene molecules. Under the action of mercuric acetate in acetic acid, diene I gives an exo—cis -adduct to the FCCF bond ( IIb ) as well as one to the HCCH ( IIc ) in a 3:2 ratio. Adduct IIb reacts with excess Hg(OCOCH 3 ) 2 and isomerizes to the tricyclic exo,exo -adduct IId . Diene IV , i.e. 2,3-difluoro-1,4,4a,5,8,8a-hexahydro-1,4,5,8-dimethanonaphthalene, reacts with anhydrous CF 3 COOH adding two molecules of the acid non-stereospecifically to both double bonds, and giving a mixture of isomeric bis-adducts V . A mixture of the monoadducts to the FCCF and HCCH bonds is formed in a 1:1.7 ratio when IV interacts with CF 3 COOH in CH 2 Cl 2 . It is notable that addition to the FCCF bond leads to the exo -trifluoroacetate VIa whereas reaction with the HCCH bond gives a mixture of exo - and endo -trifluoroacetate, VIb and VIc . The relative activities of the double bonds in I and IV are discussed.