Summary of Two-Dimensional Methods

Further 2D methods are necessary if the structure is not learned in the process of making spectral assignments for hypothetical or expected structures. The COSY experiment lays the groundwork for identifying structure through connectivities based on 7 cou- 

The NOESY experiment provides information about the proximity of protons and hence is used primarily for distinguishing structures that have clear stereochemical differences. For larger molecules, the ROESY experiment may offer some advantages because of its lower tendency to exhibit spin diffusion. The related EXSY experiment is used only when chemical exchange is being investigated. 

The 2D INADEQUATE or INEPT-INADEQUATE experiment requires additional spectrometer time. It is usually an experiment of last resort, although specific structures may be particularly amenable to this technique—for example, when there are several quaternary carbons that prevent COSY analysis. 

For a large selection of relatively straightforward 2D spectra, see Problem 6-12. The remaining problems involve molecules of medium to high complexity, although none is so complex as to require 3D methods. 

1 The following is the 300 MHz COSY spectrum of a molecule with the formula C14H20O2.  

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