Full multinuclear resonance analysis of 4-amino-1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane

Discrimination of pseudo-meta and pseudo-para diamino-octafluoro[2.2]paracyclophanes by (1)H, (19)F, and (13)C NMR

Pseudo-meta and pseudo-para diamino-octafluoro[2.2]paracyclophanes are challenging to separate either by chromatography or recrystallization, but through the use of a mixture of the two isomers, the (1)H, (19)F, and (13)C NMR spectra of these compounds have been fully and unambiguously assigned using (1)H COSY, (1)H-(19)F HOESY, (1)H-(13)C HSQC, (1)H-(13)C HMBC, and (19)F-(13)C HSQC techniques. This permits the easy identification of either of the individual isomers. In addition, the (13)C spectrum of the pseudo-ortho analogue is reported and assigned for the first time. The gem shift effect in this series of bridge-fluorinated paracyclophanes serves to deshield (1)H resonances and shield (13)C.

Investigation of the correlations between (19)F and (1)H NMR signals for various mono- and di-substituted octafluoro[2.2]paracyclophanes

A selection of mono- and pseudo ortho di-substituted octafluoro[2.2]paracyclophane derivatives were analyzed using (19)F-(1)H HOESY, (1)H COSY and (19)F COSY techniques. This resulted in the unambiguous assignment of the (19)F and (1)H NMR resonances, and also revealed interesting solvent effects and noteworthy coupling patterns for various J(HH), J(HF), and J(FF) interactions, including observable through bond (7)J(FF) and (8)J(FF) couplings. For the four mono-substituted derivatives, the assignments were achieved through the combination of (19)F-(1)H HOESY, (1)H COSY and (19)F COSY techniques. The C(2) symmetry of the six pseudo ortho di-substituted derivatives that were examined produced simplified spectra, and careful inspection of the characteristic (1)H coupling patterns led to the assignment of (1)H signals. Therefore only (19)F-(1)H HOESY experiments were required to complete the assignments for those molecules. Refinements and alternative strategies for previous protocols are presented for the molecules that were less responsive to nuclear Overhauser effect (nOe) experiments.

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.