A One-Dimensional Experiment Utilizing the NOE

The l-D NOE difference experiment is often preferred to the 2-D NOESY experiment because the former is more quantitative that is, the precision of the l-D experiment is finer. The l-D NOE difference experiment is accomplished by (1) selectively irradiating (saturating) 

The 1-D NOE difference experiment is normally carried out on H s, and is an excellent way of determining cis-trans substitution patterns of groups across carbon-carbon double bonds. The 1-D NOE difference experiment is also useful in determining the proximity of H-containing functional groups in cyclic or other molecules locked into specific conformations because of steric constraints. 

Irradiation of multiple resonances is possible, but each resonance being irradiated requires the digitization of an additional FID. That is, the control FID can be used over and over by subtracting it from each digitized FID collected when a unique resonance is saturated. 

The NOE difference experiment is carried out as follows. First, we collect a regular 1-D spectrum. Next, we record the transmitter offset required to make each resonance to be irradiated on resonance. Third, we find a suitable location in or near the spectral rvindow for dummy (or control) irradiation (perhaps —5 ppm or +15 ppm) where no resonances are observed. Fourth, we prepare both FlDs using a long period of single-frequency low power RF irradiation followed by a hard 90° RF pulse, except that in the preparation of the 

If our instrument is appropriately equipped, we can use shaped RF pulses to selectively excite resonances. We might wish to do this if using CW, RF is not selective enough. This practice is required in cases where the resonance to be irradiated is near other resonances in the spectrum (not in space) whose irradiation might yield ambiguous results. 

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