3 TRANS-DIPHENYLPERFLUOROTRIENES

The structures of uoro-2,5-bis-(pentafluorophenyl)-2,3,4-hexatriene, ( 1), C18F16, -1,1,1,2,2,7,7,8,8,8-decafluoro-3,6-diphenyl-3,4,5 octatri ene,(2), C20H10F10, and (E)-1,1,1,2,2,3,3,8,8,9, ,10-tetradecafluoro-4 ,7-diphenyl-4,5,6-decatriene, (3), C22H10F14, confirm the trans confor mation assigned by spectrophotometric methods. These trienes exhibit t he central double-bond shortening observed in cumulenes. The phenyl ri ngs are rotated slightly from the triene plane in (2) and (3) and are nearly perpendicular to the triene plane in (1). The large rotation of the perfluorophenyl rings from the triene plane is due to intramolecu lar steric interactions with the ortho-F atoms.