NMS Spectroscopy:

In this course, you have so far learnt about various spectroscopic methods involving quantised electronic, rotational and vibrational energy states of molecules and the electronic states of atoms. Within these techniques, molecules and atoms are subjected to electromagnetic radiation of appropriate wavelength and resultant absorption, emission or scattering of radiation is measured. Now you will learn about nuclear magnetic resonance (NMR) spectroscopy where transitions between different nuclear spin states are involved. The quantised nuclear spin states come into existence when the sample is placed in an external magnetic field.

In this unit, you would learn about the theory behind the phenomenon of NMR and the types of nuclei that exhibit it. Subsequently you will learn about the characteristics such as chemical shift, spin-spin coupling etc. of NMR spectra, their origin, the factors affecting them and the structural information carried by them. This will be followed by the instrumentation and the experimental set up required to obtain the NMR spectra. In the end we will discuss about some applications of NMR spectroscopy. You must have heard of MRI which is a modern medical diagnostic tool. MRI is also based on the phenomenon of nuclear magnetic resonance and finds widespread applications in the field of medicine.

Objectives

After studying this unit, you should be able to:

• state the category of nuclei that show the phenomenon of NMR,
• elaborate the basic principle of NMR,
• figure a schematic diagram of NMR spectrometer,
• describe the basic principle and advantages of Fourier transform NMR,
• define the relaxation phenomenon and its mechanism,
• describe and explain chemical shift and state the factors affecting it,
• describe the process of spin-spin splitting,
• associated the NMR spectrum of simple molecules with their structure, and
• define the applications of NMR spectroscopy in structure elucidation.