Setting Pulse Lengths and Delays

A number of parameters have to be chosen when recording 2D NMR spectra (a) the pulse sequence to be used, which depends on the experiment required to be conducted, (b) the pulse lengths and the delays in the pulse sequence, (c) the spectral widths SWi and SW to be used for Fx and 7 2, (d) the number of data points or time increments that define /, and 2. (e) the number of transients for each value of t, (f) the relaxation delay between each set of pulses that allows an equilibrium state to be reached, and (g) the number of preparatory dummy transients (DS) per FID required for the establishment of the steady state for each FID. Table 3.1 summarizes some important acquisition parameters for 2D NMR experiments. 

The choice of the pulse sequence to use is of fundamental importance. We must decide carefully what information is required, and choose the right experiment to provide it. Although hundreds of 2D pulse sequences are now available for various experiments, only some have proven themselves to be of general utility. Only such proven techniques should be chosen to solve structural problems. 

Accurate calibration of pulse lengths is essential for the success of most 2D NMR experiments. Wide variations ( 20%) in the setting of pulse lengths may significantly reduce sensitivity and may lead to the appearance of artifact signals. In some experiments, such as inverse NMR experiments, accurately set pulse lengths are even more critical for successful outcomes. 

N = TDi = number of FIDs, domain N2 = TD2 = number of total t domain 

SI] = total number of data point (size) SI2 = total number of data point (size) 

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