4. Acquisition

Time requirement: 1.5 h

Sample: 90% 2-cyclohexen-1-one in [D₆]acetone.

Record normal ¹H and ¹³C NMR spectra of the sample, note the offset of the ¹³C carbonyl signal and the offset of the β-olefinic hydrogen (H-3) signal. You have to set:

td: 128 k
sw: 450 ppm to avoid folding
o1: on resonance of the carbonyl ¹³C signal
o2: on resonance of the β-olefinic ¹H signal (H-3)
p1: 90° ¹H decoupler pulse
p2: selective 180° ¹³C transmitter pulse [Gaussian shape, 10 ms, 58 dB]
p3: 90° ¹³C transmitter pulse
¹H spin-lock pulse for cross-polarization [1.8 ms, 50 dB]; carefully adjust the phase difference to p1
¹³C spin-lock pulse for cross-polarization [pulse length must be identical to that of ¹H spin-lock pulse]; adjust with ¹³C transmitter attenuation [1.8 ms, 47 dB]
duration of spin-lock ≈ 1/J(C,H) = 125 ms, calculated from ³J(C,H) ≈ 8 Hz (one cycle of WALTZ-16)
d1: 10 s
d2: 1/[2J(C,H)] = 100 ms, calculated from ⁿJ(C,H) ≈ 6 Hz
g1–g3: sinusoidal-shaped field gradients, 1.5 ms duration and ca. 0.2 T/m strength for the largest gradient, with gradient loop counters, ring-down delays (100 μs), lock blanking and gradient coil blanking switches according to actual instrumentation used. Gradient strength ratio: −5 : 75 : 80.
decoupler attenuation and 90° pulse for CPD
ns: 512

5. Processing

Use standard 1D processing as described in Experiment 3.1 with zero-filling to 128 k and apply an exponential window with lb = 0.5 Hz.

6. Result

The figure shows the GRECCO spectra obtained on an AMX-500 spectrometer with a BGU (10 A) gradient unit using an inverse proton-optimized gradient probe-head. Unfortunately this is not the best choice for this experiment, but ¹³C-optimized gradient probe-heads were not available when this experiment was developed. a is the signal of C-5 (J(C1,C5) = 1.6 Hz) and b is the signal of C-4 (J(C1,C4) = 4.8 Hz). Note that the strong signal of the carbonyl ¹³C nucleus is present in these spectra, but is outside the region shown. Compare the excellent suppression of the center line with the result of Experiment 7.7.