4. Acquisition

Time requirement: 2 h

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

Prior to the experiment you have to determine the r.f. attenuation and phase for a selective ¹³C pulse on carbon as described in Experiment 7.1. Record a normal ¹³C NMR spectrum of the sample and adjust the spectral width to the aliphatic region. Note the offsets for the three signals of the aliphatic carbon nuclei and adjust the frequency of the selective pulse to one of them. You have to set:

decoupler attenuation and 90° pulse for CPD
td	16 k
sw	23 ppm
o1	on resonance of selected signal. If the software allows offsets for selective pulses, one can also set o1 in the middle of the ¹³C NMR spectrum. However, the different phases of the selective pulses at different offsets must be determined.
o2	middle of ¹H NMR spectrum
p1, p3	90° ¹³C transmitter pulse
p2	180° ¹³C transmitter pulse
p4	Gaussian shaped ¹³C transmitter pulse, 10 ms length, attenuation corresponding to 270° excitation, which gives better phase behavior of the satellites than with a 90° pulse.
d1	4 s
d2	1/[4J(C,C)] = 7.6 ms calculated from ¹J(C,C) = 33 Hz; for the determination of long-range couplings use d2 = 62.5 ms corresponding to ⁿJ(C,C) = 4 Hz
d3	10 μs
ds	4
ns	256

5. Processing

Use standard ¹³C NMR processing as described in Experiment 3.2. Note that the experiment yields ¹³C satellites in antiphase. The residual signal of the molecules containing only one ¹³C atom should not be used for phasing.

6. Result

In the figure a is the normal ¹³C NMR spectrum of the region of aliphatic C nuclei, obtained on an AMX-500 spectrometer. In b, C-4 was irradiated, giving a response of C-5 with J(C,C) = 33.4 Hz. In c, C-5 was irradiated, giving a response of both C-4 and C-6 with J(C,C) values of 33.4 Hz and 31.7 Hz respectively, and in d, C-6 was irradiated giving a response of C-5 with J(C,C) = 31.7 Hz. In e the selective pulse was ad-