Generating a second dimension

No matter what the nature of the interaction to be mapped, all two dimensional sequences have the same basic format and can be subdivided into four well defined units termed the preparation, evolution, mixing and detection periods (Fig. 5.1). The preparation and mixing periods typically comprise a 

To illustrate the required procedure consider a simple pulse sequence in which both the preparation and mixing units of Fig. 5.1 are each single 90 pulses (Fig. 5.2) acting on a sample that contains only a single, uncoupled proton resonance, say chloroform, with a chemical shift offset of v Hz. Viewing events with the vector model (Fig. 5.3) the initial 90 pulse places the equilibrium magnetisation in the x-y plane along the - -y-axis, after which 

Before moving on, a comment on the presentation of 2D spectra is required. The spectra of Figs. 5.6 and 5.9 have been presented in the stacked-plot mode to emphasise the similarity with one-dimensional spectra, and the presence of two frequency axes and one intensity axis. Although these may look aesthetically impressive, this form of presentation is of little use in practice. The usual way to present 2D spectra is via contour plots , in which peak intensities are represented by contours, as a mountain range would be represented on a map. Fig. 5.10 shows the equivalent contour presentation of Figs. 5.6 and 5.9 and unless stated otherwise, all 2D spectra from now on will make use of this contour mode. 

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