From Interpreting Organic Spectra

Overview

13 C NMR spectroscopy tells us about the environments of the carbon atoms in a molecule. The technique of NMR can be applied only to atoms which have nuclear spin; when they are placed in a strong magnetic field, the nuclear spins can take up different orientations which are at different energy levels. For nuclei with nuclear spin of 1/2, such as 1H, 13C, 19F and 31P, the nuclei orient themselves in one of two ways [*]. When the nucleus is irradiated with radiation of the appropriate frequency (radiofrequency), some of the nuclei in the lower energy state absorb radiation and are raised to the higher energy state. When irradiation stops, they relax to the equilibrium distribution. This relaxation process is quite slow.

The frequency of the radiation absorbed depends on the magnetic field applied to the nucleus. The field is normally made up of three components:

  1. The externally applied field. This is an extremely powerful magnetic field. When a field of 23.49 kilogauss is applied toa carbon nucleus, it absorbs radiation at 25.14 MHz. The same field, applied to a hydrogen nucleus, would make it absorb radiation at 100 MHz. Since most machines run 13 C and 1H NMR spectra, the radiation absorbed by the latter is often used to describe the power of the machine. Thus, a machine with a field of 23.49 kilogauss would be described as a 100 MHz spectrometer. To attain high, stable magnetic fields, superconducting...

Copyright The Royal Society of Chemistry 2000 under license agreement with Books24x7

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Topics of Interest

In this chapter, as in all further chapters, only decoupled 13C NMR spectra are given. Instead of DEPT spectra, an indication of whether each peak represents C, CH, CH 2 or CH 3 is given on the...

Overview 1H nuclear magnetic resonance spectroscopy tells us about the environment of the hydrogen atoms in a molecule. The technique is based on exactly the same principles as 13C NMR spectroscopy:...

Daniel J. Schaefer General Electric Medical Systems, Milwaukee, Wisconsin 24.1 INTRODUCTION Atomic nuclei containing odd numbers of nucleons (i.e., protons and neutrons) have magnetic moments.

FUNDAMENTALS OF THE QUANTITATIVE NMR by John Edwards [*] Nuclear Magnetic Resonance (NMR) spectroscopy is one of the most powerful experimental methods available for atomic and molecular level...

Nuclear magnetic resonance detectors are used when certain nuclei with odd numbered masses spin about an axis in a random fashion. When placed between poles of a strong magnet, the spins are aligned...

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