1: Basic NMR Theory
- Page ID
- 77720
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This section presents a basic overview of the theory of modern NMR. Readers interested in more in-depth treatments of this subject are encouraged to utilize the resources listed in the reference page at the end of this section. The embedded animations in the web book http://www.cis.rit.edu/htbooks/nmr/ authored by Professor Hornak makes this site especially useful for students learning about NMR.
This section will help you answer the following questions:
- 1.1: What is spin?
- The fundamentals of NMR begin with the understanding that a nucleus belonging to an element with an odd atomic or mass number has a nuclear spin that can be observed. Examples of nuclei with spin include 1H, 3H, 13C, 15N, 19F, 31P and 29Si. All of these nuclei have a spin of ½. Other nuclei like 2H or 14N have a spin of 1. Nuclei with even atomic and mass numbers like 12C and 16O have spin of 0 and cannot be studied by NMR. The following introductory discussion of NMR is limited to spin ½ nuclei
- 1.9: What is the Free Induction Decay?
- The signal we detect is called a Free Induction Decay and is produced by the macroscopic magnetization after the pulse. The magnetization will undergo several processes as it returns to equilibrium. First immediately after the pulse, the transverse component of the macroscopic magnetization will begin to precess at its Larmor frequency. This precessing magnetization will induce an alternating current in a coil (the same one used to generate the rf pulse) wound round the sample.
- 1.10: How do T₁ and T₂ relaxation affect NMR spectra?
- The decay of the FID corresponds to the loss of intensity of the macroscopic magnetization vector in the xy plane (called the transverse plane) by a process called spin-spin relaxation (or transverse or T2) relaxation. The recovery of magnetization along the z (longitudinal) axis to its equilibrium position occurs by a process called spin lattice (or longitudinal or T1 relaxation). T1 relaxation occurs through interactions of the nuclei with the lattice.