Nuclear Magnetic Resonance Spectroscopy (Wenzel)

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Page ID: 79271

Thomas Wenzel
Bates College

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Learning Objectives

After completing this unit, a student will be able to:

Explain the origins of the two energy levels involved in NMR transitions.
Explain what happens to a hydrogen nucleus during the excitation process.
Describe the importance of the populations of the two energy states as it affects sensitivity and coupling constants.
Describe the two processes by which excited state nuclei relax back to the ground state.
Explain the advantages of having a larger applied magnetic field and provide the rationale for each of these advantages.
Describe the origin of electron shielding.
Explain the origin of nuclear coupling.
Predict the multiplet nature of the resonance of a hydrogen atom due to coupling.
Identify the parameters that influence the magnitude of a coupling constant.
Predict the number of resonances and their multiplet nature for compounds undergoing slow and fast exchange.
Explain the classical description of NMR spectroscopy and how it is consistent with the quantum mechanical description.
Explain the complete process by which it is possible to obtain a free induction decay.
Describe the normal pulse sequence used in Fourier transform NMR.
Describe methods or strategies that can be used to improve the sensitivity of NMR.
Explain why resonances with long relaxation times have diminished signal and describe how magnetic resonance imaging can be used to generate an image.

The goal of this unit is to develop introductory concepts on nuclear magnetic resonance (NMR) spectroscopy that are most relevant for undergraduate chemistry majors. Development of the concepts of NMR is accomplished through an examination of the normal hydrogen (¹H) nucleus. The unit is focused on understanding what occurs in molecules and within the NMR spectrometer that causes ¹H NMR spectra to look the way they do. There is less of an emphasis on interpreting NMR spectra, although the concepts developed herein provide students with the understanding needed to begin interpreting NMR spectra. Components of both a quantum mechanical and classical description of NMR spectroscopy are developed.