are rather similar at lower field strengths. Tune the probe-head to ¹⁷O on the observe channel and locate the ¹⁷O signal using a sample of D₂O, since the ¹⁷O content of D₂O is higher than that of normal water. Determine the 90° pulse for ¹⁷O with this sample and use it as reference standard. After loading the RIDE pulse sequence you have to set:

td	4 k
sw	500 ppm
o1	200 ppm above the frequency of the ¹⁷O water signal
p1, p2, p4, p6	90° ¹⁷O transmitter pulse
p3, p5	180° ¹⁷O transmitter pulse
d1	10 ms
d2	0.5 μs
preacquisition delay	15 μs
ns	4×128

5. Processing

Use standard 1D processing as described in Experiment 3.2 with exponential multiplication (lb = 200 Hz).

6. Result

Oxygen-17 RIDE spectrum of ethyl crotonate

The figure shows the 54.24 MHz ¹⁷O NMR spectrum obtained on an AM-400 spectrometer with a 5 mm inverse multinuclear probe-head. A carboxylic ester gives two signals, one for the C=O oxygen (here at δ_O = 336) and one for the C–O oxygen (here at δ_O = 162). As an exercise record a normal ¹⁷O NMR spectrum and compare the baseline roll.