Peak Shapes in 2D NMR Spectra

The apodization functions mentioned earlier have been applied extensively in ID NMR spectra, and many of them have also proved useful in 2D NMR spectra. Before discussing the apodization functions as employed in 2D NMR spectra we shall consider the kind of peak shapes we are dealing with. 

Two-dimensional spectra are often recorded in the absolute-value mode. The absolute value A is the square root of the sum of the squares of the real (R) and imaginary (/) coefficients  

Although this eliminates negative contributions, since the imaginary part of the spectrum is also incorporated in the absolute-value mode, it produces broad dispersive components. This leads to the broadening of the base of the peaks ( tailing ), so lines recorded in the absolute-value mode are usually broader and show more tailing than those recorded in the pure absorption mode. 

What are the common peak shapes, and why it is necessary to know the peak shapes before applying apodization  

Some of the apodization functions described in Section 1.3.11 can also be adopted for use in 2D spectra. The types of functions used will vary according to the experiment and the information wanted. 

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