Comparison of ¹H–¹⁹F two‐dimensional NMR scalar coupling correlation pulse sequences

Abstract

The effectiveness of hetero-COSY, HETCOR, HMQC, and HSQC two-dimensional NMR pulse sequences for detection of (19)F-(1)H correlations by scalar coupling was evaluated on monofluorinated and polyfluorinated test compounds. All four of these sequences were effective in observing (1)H-(19)F correlations, using either (19) F or (1)H as the observe nucleus. All four sequences were amenable, to some degree, to adjustment to observe larger or smaller couplings preferentially. A 1/2J echo filter was effectively applied to remove artifacts from (2)JFF strong coupling. The HETCOR experiments afforded the best overall combination of sensitivity, resolution and selectivity for JHF.

19F-centred NMR analysis of mono-fluorinated compounds

“…For this task a choice of three types of experiment exist: hetero-COSY, HETCOR or HMBC. 31,32 Most of these can be implemented using 19 F or 1 H as the directly detected nucleus. Using 19 F as the directly detected nucleus, the 2D 1 H, 19 F HMBC has the highest sensitivity, but yields mixed-phased multiplets.…”

Fluorine Labeling of ortho-Phenylenes to Facilitate Conformational Analysis

“…It is clear, however, that there are additional conformations present in oP 6 F 3 that cannot be easily quantified using the 1D 1 H NMR spectrum because of signal overlap.The 19 F{ 1 H} NMR spectra of both hexamers, shown in Figure3b, are, of course, much simpler than the 1 H NMR spectra. Using the 1 H assignments, the major signals could be unambiguously identified by the 1 H-19 F hetero-COSY spectra in Figure4a 47,48. Both 19 F{ 1 H} NMR spectra also show sets of smaller signals, which were confirmed to be from minor conformers by the 19 F-19 F EXSY spectra in Figure4b 49.…”

New 19F NMR methodology reveals structures of molecules in complex mixtures of fluorinated compounds

“…The chemical shift correlation experiments involving 19 F have evolved together with general improvements of liquidstate NMR methodology; 75 most notably the use of adiabatic 19 F inversion pulses is now widespread. 66,[76][77][78] Nevertheless, even some more resent 19 F experiments yield magnitude mode spectra, 76,78 provide correlation but not the values of coupling constants, 76 or contain refocusing periods that generally decrease their sensitivity. 77,78 Some phase sensitive experiments yield complicated cross peak structures, thereby lowering their sensitivity.…”

“…66,[76][77][78] Nevertheless, even some more resent 19 F experiments yield magnitude mode spectra, 76,78 provide correlation but not the values of coupling constants, 76 or contain refocusing periods that generally decrease their sensitivity. 77,78 Some phase sensitive experiments yield complicated cross peak structures, thereby lowering their sensitivity. [79][80][81] The new NMR experiments presented here build on these advances, are phase sensitive and produce cross peaks with a simple pattern that allow identification of active coupling constants.…”