U. of Ottawa NMR Facility Blog 1H J-Resolved Spectroscopy to Evaluate 1H-1H and 1H-19F Coupling Constants

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[U. of Ottawa NMR Facility Blog] 1H J-Resolved Spectroscopy to Evaluate 1H-1H and 1H-19F Coupling Constants

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02-29-2020, 09:52 PM

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1H J-Resolved Spectroscopy to Evaluate 1H-1H and 1H-19F Coupling Constants

1H J-Resolved Spectroscopy to Evaluate 1H-1H and 1H-19F Coupling Constants

2D 1H J-RESolved spectroscopy (JRES) is able to separate the 1H chemical shift and J coupling interactions in the F2 and F1 domains of the 2D data, respectively. The F2 projection represents the pure-shift 1H decoupled 1H NMR spectrum while the individual F1 slices at each chemical shift reveal the 1H - 1H J coupling for each resonance. When this technique is applied to a spin system with both homonuclear 1H-1H coupling and heteronuclear coupling, it has the ability to provide both the homonuclear and heteronuclear coupling constants. This is demonstrated in the figure below for 2,3-difluoro pyridine which has both 1H-1H and 1H-19F coupling.

The top trace in the figure is the 1H NMR spectrum showing the complex resonances due to both the homonuclear and heteronuclear coupling. The 2D JRES spectrum is highlighted in grey. The 1H-1H coupling is shown in the F1 slices which were summed to produce the blue, red and green vertical traces in the figure for 1H resonances A, C and B, respectively. These traces are identical to the resonances in the separately collected 1H spectrum with 19F decoupling shown in the bottom trace of the figure. The F2 projection of the JRES spectrum is shown in the trace directly on top of the 2D spectrum, colour coded in yellow. The F2 projection represents the 1H decoupled 1H spectrum showing only the 1H- 19F coupling. It can be compared to the separately collected PSYCHE pure-shift 1H spectrum, colour coded in orange which is very nearly identical. Clearly this very simple, often overlooked, technique can provide a great deal of both homonuclear and heteronuclear coupling information.

Source: University of Ottawa NMR Facility Blog

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