4. Acquisition

Time requirement: 40 min Sample: 5% ethyl crotonate in CDCl₃ Record normal 1D ¹H and ¹³C NMR spectra, optimize the spectral widths, and note the offsets. Switch to the 2D mode of the spectrometer software, load the HMQC pulse program, and, if required, change the spectrometer to the inverse set-up. You have to set:

td2: | k data points in F, tdl: 128 data points in F; sw2: 8 ppm sw: 175 ppm offset of ¹H frequency: middle of ¹H NMR spectrum offset of ¹³C frequency: middle of ¹³C NMR spectrum p!: 90° ¹H transmitter pulse p2: 180° ¹H transmitter pulse p3, p4: 90° ¹³C decoupler pulse dl:2s d2: 1/[2(C,H)] = 3.5 ms, calculated from 'J(C,H) = 145 Hz initial value for ¢, evolution: 3 μs increment for ¢, evolution: |/[2-sw1] ds: 2

5. Processing

Apply zero-filling in F, to 256 real data points to obtain a matrix of 512256 real data points. Use 2/2-shifted squared sinusoidal windows in both dimensions. Apply complex Fourier transformation corresponding to the N-type signal selection using the quadrature-off mode in F;. Phase correction is not necessary, since the data are proc- essed in magnitude mode.

6. Result

The figure shows the HMQC spectrum obtained on an ARX-200 spectrometer with a normal forward dual probe-head. This demonstrates that a special inverse probe-head is not an absolute necessity. Note that the spectrum displays doublets in F, with the spin coupling constant 'J(C,H), and in addition the homonuclear splittings caused by H,H spin couplings. These also broaden the signals in the F, dimension. There is considerable signal breakthrough from the protons bonded to ¹³C, which is seen mostly for the methyl! group signals.