Non-bond FF nuclear spin couplings II. Hexafluoropropene trimers

Variable-Temperature 19F NMR and Theoretical Study of 1,9- and 1,7-C60F(CF3) and Cs- and C1-C60F17(CF3): Hindered CF3 Rotation and Through-Space JFF Coupling

“…The term “through-space coupling” is defined here as Fermi contact coupling (FCC) by direct overlap of fluorine atom orbitals (primarily lone-pair orbitals) as opposed to FCC through the σ framework of a molecule, a definition that has been used by NMR spectroscopists for more than 40 years . It is now widely accepted that significant J coupling between proximate fluorine nuclei (i.e., ≤3.2 Å apart) that are separated by four or more bonds (i.e., ≥4 J FF ) is mediated predominantly through space (as just defined) and not through the network of covalent bonds that separate the fluorine atoms. ,,,− The most convincing case is the 17 ± 2 Hz 398 J FF coupling observed for the fluorine atoms on 6-fluorotryptophan residues (Trp5 and Trp133) in a dihydrofolate reductase−NADPH−MTX protein complex, which Oldfield and co-workers later showed was mediated entirely by through-space coupling (F···F = 2.98 Å) …”

“…Experimental and theoretical studies have shown that 37−99 Hz ≥4 J FF values can occur when two C−F bonds are oriented so that the F···F distance is between 2.7 and 2.5 Å. − ,,, Given that the magnitude of the J FF through-space component is known to depend on the relative orientations of the C−F bonds, the five 4 J FF values observed for 1,9-C 60 F(CF 3 ), C s -C 60 F 17 (CF 3 ), and C 1 -C 60 F 17 (CF 3 ) with F···F distances between 2.61 and 2.71 Å, which range from 19 to 48 Hz, are consistent with predominantly through-space coupling. A plot of F···F distance vs 4,5 J FF for these three compounds is displayed in Figure , which also shows some of the relative orientations of the pairs of C−F bonds as well as the F−C···C−F torsion angle dependence for the 19, 25, and 27 Hz 4 J FF values that correspond to F···F distances of 2.65, 2.66, and 2.71 A, respectively.…”

“…40 It is now widely accepted that significant J coupling between proximate fluorine nuclei (i.e., e3.2 Å apart) that are separated by four or more bonds (i.e., g4 J FF ) is mediated predominantly through space (as just defined) and not through the network of covalent bonds that separate the fluorine atoms. 25,26,28,[41][42][43][44] The most convincing case is the 17 ( 2 Hz 398 J FF coupling observed 45 for the fluorine atoms on 6-fluorotryptophan residues (Trp5 and Trp133) in a dihydrofolate reductase-NADPH-MTX protein complex, which Oldfield and co-workers later showed was mediated entirely by through-space coupling (F‚‚‚F ) 2.98 Å). 25 Experimental and theoretical studies have shown that 37-99 Hz g4 J FF values can occur when two C-F bonds are oriented so that the F‚‚‚F distance is between 2.7 and 2.5 Å.…”

“…25 Experimental and theoretical studies have shown that 37-99 Hz g4 J FF values can occur when two C-F bonds are oriented so that the F‚‚‚F distance is between 2.7 and 2.5 Å. [25][26][27]42,44,46 Given that the magnitude of the J FF through-space component is known to depend on the relative orientations of the C-F bonds, the five 4 J FF values observed for 1,9-C 60 F(CF 3 ), C s -C 60 F 17 (CF 3 ), and C 1 -C 60 F 17 (CF 3 ) with F‚‚‚F distances between 2.61 and 2.71 Å, which range from 19 to 48 Hz, are consistent a Temperature at which a slow-exchange limit spectrum was obtained unless otherwise noted. b Enthalpy of activation for CF3 rotation.…”

Facile hydrophobic modification of hybrid poly(urethane-urea)methacrylate aqueous dispersions and films through blending with novel waterborne fluorinated acrylic copolymers

“…In particular, similar mass spectra were collected from the two most abundant species (about 80% of the total isomeric mixture according to the uncorrected integrated areas of the GC peaks), with three main MS fragments at 431, 405, and 343 M/+ consistent with the fragmentations of both structural isomers (the a and b forms in Scheme 2 are rotamers and 3 is in fact an enantiomeric mixture). 19 F NMR analysis of the isomeric mixture gave a complex spectral pattern with a good match with the expected resonances from the four rotamers corresponding to the two structural isomers [31,32] (Fig. 1).…”