Introduction to Two-Dimensional Spectroscopic Methods

In a normal pulsed NMR experiment, the 90° excitation pulse is followed immediately by a data acquisition phase in which the FID is recorded and the data are stored in the computer. In experiments that use complex pulse sequences, such as DEPT, a preparation phase is included before data acquisition. During the preparation phase, the nuclear magnetization vectors are allowed to process, and information may be exchanged between magnetic nuclei. In other words, a given nucleus may become encoded with information about the spin state of another nucleus which may be nearby. 

Of the many types of two-dimensional experiments, two find the most frequent application. One of these is H—H Correlation Spectroscopy, better known by its acronym, COSY. In a COSY experiment, the chemical shift range of the proton spectrum is plotted on both axes. The second important technique is Heteronuclear Correlation Spectroscopy, better known as the HETCOR technique. In a HETCOR experiment, the chemical shift range of the proton spectrum is plotted on one axis, while the chemical shift range of the C spectrum for the same sample is plotted on the second axis. 

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