4. Acquisition

Time requirement: 15 min Sample: 3% strychnine in CDCl₃ Run a normal ¹H NMR spectrum of the sample, optimize the spectral width, and note the offsets of the signals to be irradiated. You have to set:

sw: 10 ppm o1: middle of ¹H NMR spectrum p1, p4, p6: 90° ¹H transmitter pulse p2, p3: selective 180° ¹H transmitter pulse, Gaussian shape, 50 ms length, off- set modulated with the difference 4 between o1 and the offset of the signal to be irradiated, transmitter attenuation corresponding to 180° [65 dB] p5: 180° ¹H transmitter pulse dl:2s d2: mixing time delay 0.5 s, total mixing time 7, = d2 + g5 + p5 + g6 + d3 d3: mixing time delay, set to 0.4-d2 g1–g6: sinusoidal-shaped field gradients with 1% truncation, | ms duration and ca. 0.1 T/m strength, with gradient loop counters, ring-down delays (100 μs), lock blanking and gradient coil blanking switches according to actual instrumentation used. Gradient strength ratio: 20 : -20 ds: 4

5. Processing

Use standard 1D processing as described in Experiment 3.1 with exponential multiplication (lb = 0.3 Hz). Adjust a negative phase for the irradiated multiplet.

6. Result

The figure shows the result obtained on an AMX-500 spectrometer with a BGU (10 A) gradient amplifier in a 5 mm inverse gradient probe-head. a is the normal ¹H NMR spectrum. In b the selective pulse was adjusted on the signal of H-16 at 6; = 3.79;

strong NOE effects are observed for one H-18 (64 = 2.8), one H-11 (6; = 2.58), H-17 (dy = 1.8), and H-13 (6; = 1.19). Note the very small NOE effect for H-12 (&; = 4.2) and the small negative effect for the other H-18 (&, = 3.15). In ¢ the selective pulse was adjusted to the signal of H-20 at 6; = 3.65; NOE effects are observed for the other H-20 (6; = 2.65) and for one H-15 (6; =2.38). A very small negative NOE effect can be observed for the other H-15 (&: = 1.36).