How simultaneous decoupling of 1H and 19F can help to simplify crowded 13C spectra – A Multi-nuclei case study on 5-Bromo-1,2,3-trifluorobenzene without the need of user invention

 1H Spectra

 

5-Bromo-1,2,3-trifluorobenzene (BrC6H2F3) is a structurally simple molecule commonly used as a building block in a variety of synthetic organic reactions. As this molecule contains 1H, 19F, and 13C (in natural abundance), it is a beautiful example to demonstrate the unique advantage offered by the Spinsolve of accessing all three nuclei simultaneously without requiring retuning or user intervention.  Figure 1 shows the 1H NMR spectrum of neat 5-Bromo-1,2,3-trifluorobenzene measured in a single scan taking 10 seconds to acquire (top) and the respective 1D proton 19F decoupled spectrum (bottom). As no retuning of the probe is required to switch from 1H and 19F, the 1H signal can be acquired while the 19F nuclei are being decoupled.

 

Figure 1: 1H NMR spectrum of neat 5-Bromo-1,2,3-trifluorobenzene measured on a Spinsolve 80 MHz system in a single scan

19F Spectra

 

5-Bromo-1,2,3-trifluorobenzene is a good example to highlight the advantage of 19F protocols with 1H decoupling possibilities. The usual 19F NMR spectrum (top spectrum) allows one to identify the two expected 19F resonances for the fluorine atoms at positions 8, 9, and 10. The bottom spectrum shows the 1H decoupled 19F NMR spectrum. The multiplet structure of each peak is defined only by the fluorine couplings, so as expected we can observe a triplet at position 9 and a doublet at positions 8 and 10.

 

Figure 2: 19F NMR spectrum of neat 5-Bromo-1,2,3-trifluorobenzene measured on a Spinsolve 80 MHz system in a single scan. With (bottom) and without (top) 1H decoupling.

13C Spectra

 

Figure 3 shows the 13C NMR spectra of neat 5-Bromo-1,2,3-trifluorobenzene acquired using NOE polarization transfer. The top spectrum was measured without any decoupling. It clearly resolves the expected resonances but shows a crowded multiplicity structure for each carbon. The 1D carbon acquired with 1H decoupling (middle spectrum) eliminates some couplings and slightly simplifies some of the peaks, but only the 1D carbon acquired with simultaneous 1H, 19F decoupling (bottom spectrum) shows a singlet for each carbon atom to clearly resolve the four expected resonances.

 

Figure 3: Carbon NMR spectra of neat 5-Bromo-1,2,3-trifluorobenzene measured on a Spinsolve 80 MHz system using NOE (top), 1H decoupling (middle), and 1H,19F decoupling sequences (bottom).

 

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