2D Heteronuclear Overhauser Effect SpectroscopY (HOESY) is an effective way to determine whether or not a pair of heteronuclear spins are close to one another in space. It is particularly effective for 1H and 19F where both nuclides are 100% naturally abundant. 2D 19F detected 19F - 1H HOESY data are typically obtained which provide all NOE correlations. 2D experiments, however, can be quite time consuming, especially when only a few NOE correlations are sought after. In such cases, 1D 1H detected 1H - 19F HOESY experiments1 are very desirable and can save a great deal of time. When only one 19F resonance is present, they can be obtained by using hard 19F pulses. This was recently illustrated well by Dr. Michael Lumsden of Dalhousie University. When more than one 19F resonance is present, one can use a selective 19F pulse and repeat the experiment selecting each type of fluorine. An example of this is shown in the figure below. Selective 1D 1H detected 1H - 19F HOESY spectra were collected for 2,3-difluoropyridine using a selective 19F pulse. The simple 19F spectra are shown on the left with the selected 19F resonance color coded. The upper two spectra on the right are the HOESY spectra while the spectrum on the bottom right is a simple 1H spectrum. One can see that when the fluorine in the 3-position is selected, there is a strong NOE to the nearest proton, C. Alternatively, when the fluorine in the 2-position is selected, there are no strong NOE's as there are no adjacent protons.
1. L.E. Combettes, P. Clausen-Thue, M.A. King, B. Odell, A.L. Thompson, V. Gouverneur and T.D.W. Claridge. Chem. Eur. J. 18, 13133 (2012).