4. Acquisition

Time requirement: 9h 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 phase-sensitive HMBC pulse program including the BIRD filter and, if required, change the spec- trometer to the inverse set-up. You have to set:

td2: | k data points in F> td1: 128 data points in F; sw2: 8 ppm swl: 175 ppm offset of ¹H frequency: middle of ¹H NMR spectrum offset of ¹³C frequency: middle of ¹³C NMR spectrum p1, p3, p4: 90° ¹H transmitter pulse p2, p5: 180° ¹H transmitter pulse p7, p8, p9: 90° ¹³C decoupler pulse p6: 180° ¹³C decoupler pulse dl: 1s d2: 1/[2 J(C,H)] = 50 ms, calculated from "J(C,H) = 10 Hz d3: BIRD delay to be optimized for minimum FID, ca. 1 s; observe the incom- ing FID in the set-up mode and adjust d3 for minimum intensity (see Exp. 6.14) d4: 1/[2(C,H)] = 3.5 ms, calculated from 'J(C,H) = 145 Hz d5: 46.5 ms (d5 = d2 – d4) initial value for ¢; evolution: 3 μs increment for ¢, evolution: 1/[4-sw1] ds: 2

5. Processing

Apply zero-filling in F; to 256 real data points to obtain a matrix of 512x256 real data points. Use exponential or Gaussian windows in both dimensions. Apply real Fourier transformation corresponding to the TPPlI-type signal selection using the quadrature mode in F;. Phase correction in both dimensions is required.

6. Result

The figure shows the HMBC 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 2D spectrum shown is split into two different ranges, since it is