1D Selective 1H - 19F HOESY

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).