1 H NMR spectroscopy is a powerful tool for the conformational analysis of orthophenylene foldamers in solution. However, as o-phenylenes are integrated into evermore-complex systems, we are reaching the limits of what can be analyzed by 1 Hand 13 C-based NMR techniques. Here, we explore fluorine labeling of o-phenylene oligomers for analysis by 19 F NMR spectroscopy. Two series of fluorinated oligomers have been synthesized. Optimization of monomers for Suzuki coupling enables an efficient stepwise oligomer synthesis. The oligomers all adopt well-folded geometries in solution, as determined by 1 H NMR spectroscopy and X-ray crystallography. 19 F NMR experiments complement these methods well. The resolved singlets of one-dimensional 19 F{ 1 H} spectra are very useful for determining relative conformer populations. The 1 additional information from two-dimensional 19 F NMR spectra is also clearly valuable when making 1 H assignments. Comparison of 19 F isotropic shielding predictions to experimental chemical shifts is not, however, currently sufficient by itself to establish o-phenylene geometries.
1 H NMR spectroscopy is a powerful tool for the conformational analysis of orthophenylene foldamers in solution. However, as o-phenylenes are integrated into evermore-complex systems, we are reaching the limits of what can be analyzed by 1 Hand 13 C-based NMR techniques. Here, we explore fluorine labeling of o-phenylene oligomers for analysis by 19 F NMR spectroscopy. Two series of fluorinated oligomers have been synthesized. Optimization of monomers for Suzuki coupling enables an efficient stepwise oligomer synthesis. The oligomers all adopt well-folded geometries in solution, as determined by 1 H NMR spectroscopy and X-ray crystallography. 19 F NMR experiments complement these methods well. The resolved singlets of one-dimensional 19 F{ 1 H} spectra are very useful for determining relative conformer populations. The 1 additional information from two-dimensional 19 F NMR spectra is also clearly valuable when making 1 H assignments. Comparison of 19 F isotropic shielding predictions to experimental chemical shifts is not, however, currently sufficient by itself to establish o-phenylene geometries.
¹H NMR spectroscopy is a powerful tool for the conformational analysis of ortho-phenylene foldamers in solution. However, as o-phenylenes are integrated into ever-more-complex systems, we are reaching the limits of what can be analyzed by ¹H- and ¹³C-based NMR techniques. Here, we explore fluorine labeling of o-phenylene oligomers for analysis by ¹⁹F NMR spectroscopy. Two series of fluorinated oligomers have been synthesized. Optimization of monomers for Suzuki coupling enables an efficient stepwise oligomer synthesis. The oligomers all adopt well-folded geometries in solution, as determined by ¹H NMR spectroscopy and X-ray crystallography. ¹⁹F NMR experiments complement these methods well. The resolved singlets of one-dimensional ¹⁹F{¹H} spectra are very useful for determining relative conformer populations. The additional information from two-dimensional ¹⁹F NMR spectra is also clearly valuable when making ¹H assignments. Comparison of ¹⁹F isotropic shielding predictions to experimental chemical shifts is not, however, currently sufficient by itself to establish o-phenylene geometries.
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