Resonance integral absolute magnitude

A nucleus in different enviromnents is shielded by the circulation of surrounding electrons to different extents. Different values of aB, each depending on the magnitude of the applied B are obtained for the nucleus. As B cannot be determined to the required degree of accuracy, the absolute position of absorptions cannot be obtained directly from the instrument. However, the relative position of absorption can readily be obtained with an accuracy of 1 Hz or lower. The separation of resonance frequencies of a nucleus in different stractural enviromnents from an arbitrarily chosen standard is referred to as chemical shift. A plot of the chemical shifts (frequencies of absorption peaks) versus the intensities of absorption peaks (which for some nuclei may by integration provide the number of nuclei) constitutes a NMR spectrum. The chemical shift is symbohzed by d (delta) and is measured in ppm (parts per million) according to ... 

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