4. Acquisition

Time requirement: 5 h

Sample: 20% ethyl crotonate in CDCl₃.

Record normal ¹³C and ¹H NMR spectra and optimize the spectral widths. Change to the 2D mode of the spectrometer software and load the pulse program for COLOC. You have to set:

td2: 1 k data points in F₂
td1: 64 data points in F₁
sw2: 175 ppm
sw1: 8 ppm
o1: middle of ¹³C NMR spectrum
o2: middle of ¹H NMR spectrum
p1, p3: 90° ¹H decoupler pulse
p2: 180° ¹H decoupler pulse
p4: 180° ¹³C transmitter pulse
p5: 90° ¹³C transmitter pulse
d1: 2 s
d2: 25 ms
d3: 1/[3J(C,H)] = 33 ms, calculated from ⁿJ(C,H) = 10 Hz
initial value for t₁ evolution: 3 μs
increment for t₁ evolution: 1/[2·sw1]
decrement for d2: 1/[2·sw1]; note that d2 must be larger than td1 times 1/[2·sw1]
decoupler attenuation and 90° pulse for CPD
ds: 2
ns: 128

5. Processing

Apply zero-filling in F₁ to 256 real data points. Use squared π/2-shifted sinusoidal windows in both dimensions. Apply complex Fourier transformation corresponding to the N-type signal selection using the quadrature-off mode in F₁. Phase correction is not necessary, since the data are processed in magnitude mode.

6. Result

The figure shows the 2D spectrum obtained on an ARX-200 spectrometer. Most of the cross-signals corresponding to ¹J(C,H) can still be observed. Compared with the result of Experiment 10.11, which was obtained under otherwise identical conditions, there is less noise, and the cross-peaks for H-4 to C-2, as well the cross-peak for H-5 to C-1, are much stronger; however, the correlations of H-3 and H-2 to C-1 are completely