4. Acquisition

Time requirement: 0.5 h

Sample: 20% ethyl crotonate in CDCl₃.

Prior to the experiment you have to choose a Gaussian pulse shape and to determine the attenuation and the relative phase of a selective ¹³C pulse in the inverse mode of the spectrometer (see Exp. 7.3). Record normal ¹H and ¹³C NMR spectra and note the offsets of the desired carbon signals. The sequence given above consists of the BIRD filter (see Exp. 6.14) and the actual SELINCOR sequence. You have to set:

td	32 k
sw	10 ppm
o1	middle of ¹H NMR spectrum
o2	on resonance of selected ¹³C nucleus
p1, p3, p4	90° ¹H transmitter pulse
p2, p5	180° ¹H transmitter pulse
p6	180° ¹³C decoupler pulse
p7	90° ¹³C decoupler pulse
p8	Gaussian shaped ¹³C decoupler pulse, 5 ms length, attenuation corresponding to 90° or 270° excitation.
d1	1 s
d2	1/[2J(C,H)] = 3.57 ms, calculated from ¹J(C,H) = 140 Hz
d3	BIRD relaxation delay, optimized for minimum FID intensity, [2.5 s]
d4	same length as selective pulse p8, 5 ms was used here
ds	4
ns	32

5. Processing

Use standard ¹H processing as given in Experiment 3.1. Since the phase of the satellites is not pure, process the spectrum in magnitude mode.

6. Result

The figure shows spectra obtained on an AMX-500 spectrometer. a is the normal ¹H NMR spectrum and b to e are the SELINCOR spectra, all processed in magnitude mode. In b C-2, in c C-5, in d C-4, and in e C-6 was selected. Note that the selective ¹³C pulse of 5 ms length is able to distinguish between C-4 and C-6, which are separated by 450 Hz at the field strength used, but is broad enough to cover the width of a typical C,H doublet.