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

Abstract

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.

19F chemical shifts, coupling constants and conformational preferences in monosubstituted perfluoroparacyclophanes

“…We have previously demonstrated that in mono-and di-fluoro-1,1,2,2,9,9,10,10-octafluoro [2.2] paracyclophane (fluoro-AF4s), a bridge fluorine couples with a large coupling constant (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) Hz) with the aromatic fluorine ortho and syn, and with a somehow smaller constant (20-10 Hz) with the aromatic fluorine which is pseudo-gem to the fluorine ortho and syn. [2] The other large couplings used for the assignment were the ortho coupling of the aromatic fluorines, 28-18 Hz, significantly larger than the meta or para couplings, 12-0 Hz. [6] The steps of the assignment procedure on the example of compound 2 are presented in Fig.…”

“…The mixing time was 0.01 s, the optimum value found in an array of mixing times of 0.002, 0.005, 0.01, 0.02, 0.05 and 0.1 s for pseudo-orthodifluoro-AF4. [2] The rates for rotation (k) have been measured in toluene-d 8 by line-shape analysis using gNMR, [3] in the temperature range −50 to 20…”

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

“…[1][2][3][4][5][6][7][8][9][10][11][12] The spectroscopy of these compounds is particularly interesting, and nuclear magnetic resonance (NMR) is no exception. [13][14][15][16] With the advancements in syntheses of bridge-fluorinated [2.2] paracyclophanes, [17][18][19][20][21][22][23][24][25] and their potential utility as monomers in high-performance polymers, [26,27] the spectroscopy of this class of compounds has been an area of particular interest. The presence of fluorine atoms in this class of cyclophanes render these compounds amenable to study by 19 F NMR, which is highly sensitive and intrinsically information-rich, and provides unique insight into their chemistry.…”