Mono- and difluorinated 1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophanes (AF4s)-A (1)H and (19)F NMR study

Complete assignment of the (1)H and (19)F chemical shifts in 4-fluoro-AF4 (1) were based on the nOes seen in its (19)F-(1)H HOESY spectrum. This allowed for identification of features which can further be applied to the assignment of the regiochemistry of substituted perfluoroparacyclophanes (PCPs) and AF4s: (i) an aromatic fluorine couples with the two fluorines in the closest bridge that are syn to it, with constants of ca. 20 Hz; (ii) an aromatic fluorine couples with the bridge fluorine five bonds away that is anti to it in the same paraphenylene moiety, with a constant of ca. 3.5 Hz; (iii) the geminal coupling of the bridge fluorines is 246 Hz if they have an ortho fluorine and 238 Hz if they do not; (iv) a bridge fluorine couples with those aromatic protons in the same paraphenylene moiety that are four or five bonds away and anti. These features have been used to assign the regiochemistry of the pseudo-ortho, pseudo-meta and pseudo-para-difluoro AF4s 2-4. It has also been demonstrated that SCS for the bridge fluorines can be used as well for this assignment.