4. Acquisition

Time requirement: 5 min

Sample: 1% CHCl₃ in [D₆]acetone.

First obtain normal ¹H and ¹³C spectra of the sample and note the offsets of the CHCl₃ signals. Change to the inverse mode, using the proton channel as transmitter and the ¹³C channel as decoupler. Load the pulse program for the gradient zz-filter. You have to set:

td	4 k
sw	500 Hz
offset of ¹H frequency	on ¹H resonance
offset of ¹³C frequency	on ¹³C resonance
p1, p3, p4	90° ¹H transmitter pulse
p2	180° ¹H transmitter pulse
p5	180° ¹³C decoupler pulse
d1	10 s
d2	1/[4¹J(C,H)] = 1.17 ms, calculated from ¹J(C,H) = 214 Hz
g1	sinusoidal-shaped field gradient with 5% truncation, 1.5 ms duration and ca. 0.1 T/m strength, with gradient loop counter, ring-down delay (100 μs), lock blanking and gradient coil blanking switches according to actual instrumentation used. Gradient strength to be varied for best results.
ds	4
ns	1

5. Processing

Use standard ¹H processing as described in Experiment 3.1.

6. Result

The figure shows the result obtained on an AMX-500 spectrometer with a multinuclear inverse gradient probe-head. Compare the result with the other methods described in this book to achieve a suppression of protons bonded to ¹²C (see Exps. 6.14–6.17 and 11.7).

7. Comments

The method can best be understood with the product operator formalism. Neglecting the 180° pulses, which refocus the chemical shifts, we find for a proton bonded to ¹³C the result as given in Equation (1), since by setting the delay 2·d2 = τ = 1/[2¹J(C,H)] the cosine terms become zero and the sine terms unity.