Techniques in Aid of Spectral Analysis and Assignment

As the resolution and sensitivity of commercial spectrometers have improved, NMR spectroscopists have been increasingly challenged with spectra of more complex systems. In this section we outline some of the special techniques used in assignment of resonances, determination of coupling networks, differentiation of C, CH, CH2, and CH3 groups, etc.  

3ip (99) iig (100) i3( i3(-. (djfectiy bonded) correlation maps have also been generated using double quantum transition frequencies, enhanced by INEPT. H- H shift correlation maps display cross peaks correlating shifts of groups of spin-coupled protons.  

The differentiation of CHj, CHj, CH, and quaternary carbons in a complex molecule is particularly useful if the undecoupled C spectrum is too crowded for clear identification of individual multiplets. Selective decoupling, or off-resonance 

Chain-tracing techniques for large molecules may use combinations of 2D J spectra, 2D NOE, and exchange correlation maps. A 2D INADEQUATE spectrum identifies sections of the carbon backbone of a molecule since the presence of a pair of double quantum peaks in the spectrum normally indicates a CC bond. An example of the power of 2D methods in spectral assignment and determination of structure is in the application to biopolymers.  

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