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How do I know if my unknown contains a fluorine atom(s)? … Part 4

May 1, 2008

2D NMR experiments such as 1H-13C HMQC, HSQC, and HETCOR spectra, offer the elucidator the opportunity to assess the presence of a fluorine atom(s).

The 1H -13C HSQC spectrum below is another case where a protonated carbon that experiences 13C-19F coupling shows a unique correlation pattern. The CH carbon projected on the F1 domain at 34 pm correlates with the 1H multiplet (ddt) at 2.4 ppm. The 1H multiplet overlaps with another multiplet (dd) for the CH2 resonance at 30 ppm.


The second spectrum is a close-up on the region around the 1H multiplets at 2.4 ppm. Notice the unique pattern whereby the correlations do not line-up.


For both spectra, the F1 trace is a projection of all the 13C slices and a 1D 1H NMR spectrum is attached to the F2 domain, hence the better resolution. The chemical shifts for the CH and CH2 group are shown in blue on the steroid-type fragment.


TIP: To avoid missing any extra bit of information, zoom-in on each individual HSQC correlation for a closer look at the data.


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