4. Acquisition

Time requirement: 24 h Sample: 3% strychnine in CDCl₃ Record normal 1D ¹H and ¹³C NMR spectra, optimize the spectral widths for the ali- phatic region only and note the offsets. Narrow spectral windows should be used be- cause of the digitization problem in 3D NMR. Switch to the 3D mode of the spectrometer software, and load the 3D HMQC-COSY pulse program. You have to set:

td3: 256 data points in F; (¹H) td2: 64 data points in F» (¹H) td1: 128 data points in F; (¹³C) sw3: 3.3 ppm sw2: 3.3 ppm swl: 42 ppm o1: middle of selected ¹H NMR region o2: middle of selected ¹H NMR region 03: middle of selected ¹³C NMR region p1, p3, p4, p6: 90° ¹H transmitter pulse p2, p5: 180° ¹H transmitter pulse p8, p9: 90° ¹³C decoupler pulse p7: 180° ¹³C decoupler pulse dl:2s d2: 1/[2(C,H)] = 3.5 ms, calculated from 'J(C,H) = 145 Hz d3: BIRD delay to be optimized for minimum FID, ca. 0.4 s (see Exp. 6.14) ¹³C¢ decoupler attenuation and 90° pulse for GARP initial values for ¢, and ft, evolution: 3 μs increment for ¢, evolution: 1/[4-sw1]; increment for ¢, evolution: 1/[2-sw2]

5. Processing

Apply zero-filling to 128 real data points in F, and to 256 real data points in F, to ob- tain a matrix of 128x 128x256 real data points. This will result in 4 MB of processed data, Use an exponential window with lb = 5 Hz line-broadening in Fy and 7/2-shifted squared sinusoidal windows in the other two dimensions. Apply the correct acquisition order parameter (3–1–2) before FT in all three dimensions. Phase correction is best performed after the FT of each dimension. Further details are very dependent on the particular software you use to process such a 3D data file.

6. Result

The figures show the 3D cuboid of an H,H-COSY plane (a) and a C,H plane (b), ob- tained on an AMX-500 spectrometer using a multinuclear inverse probe-head. The