ABSTRACT
The utility of NMR spectroscopy as an analytical tool stems primarily from the fact that the frequencies and intensities observed in a NMR spectrum depend upon the molecular structure and conformation of the sample. As discussed in Chapter 1 , electrons shield the nucleus from the effects of the applied magnetic field, and the resonance frequency, or chemical shift, observed for a given nucleus is a re flection of the overall electronic environment of the nucleus. Consequently, the observed chemical shifts in a NMR spectrum are dictated by the three-dimensional structure of the molecule. Additional information about molecular structure can be obtained from observation of scalar coupling (J coupling). The magnitude of this through-bond interaction is dependent on both the bonding network connecting the /-coupled nuclei and the molecular geometry. Furthermore, dipolar coupling exists between spatially close nuclei, and this interaction gives rise to a phenom enon called the nuclear Overhauser effect (NOE). Measurement of the NOE can provide detailed information about molecular structure and dynamics.
