April 28, 2008
Experiments such as 1H-13C HMQC, HSQC, or HETCOR can be used to suspect the presence of fluorine but not necessarily rule out the absence of fluorine. The stipulation behind this assessment is that a carbon from either a CH, CH2 or CH3 group must experience 13C-19F coupling(s).
The spectrum below is a region of an 1H -13C HSQC for the CH group belonging to the steroid-type fragment. The F1 trace is a projection of all the 13C slices. A 1D 1H NMR spectrum is attached to the F2 domain, hence the better resolution. The CH carbon resonances at 71 pm are split due to 13C-19F coupling. To confirm this, the 13C resonances correlate to a 1H at 4.1 ppm, which integrates to 1. A processed 1H NMR spectrum is shown on a previous blog.
TIP: Once again, the pattern to look out for is ‘doubling up tilt’ of correlations along F1.