What Is an NMR Spectrum

It is customary to measure the resonance frequencies of individual nuclei relative to the resonance frequency of the same nuclei in a reference compound. The 

Schematic diagram of a nuclear magnetic resonance spectrometer. 

When we determine a H-NMR spectrum of a compound, we report how far the resonance signals of its hydrogens are shifted from the resonance signal of the hydrogens in TMS. When we determine a C-NMR spectrum, we report how far the resonance signals of its carbons are shifted from the resonance signal of the four carbons in TMS. 

To standardize reporting of NMR data, workers have adopted a quantity called the chemical shift (S). Chemical shift is calculated by dividing the shift in frequency of a signal (relative to that of TMS) by the operating frequency of the spectrometer. Because NMR spectrometers operate at MHz frequencies (i.e., millions of Hz), we express the chemical shift in parts per million. A sample calculation is provided for the signal at 2.05 ppm in the 

Downfield A term used to refer to the relative position of a signal on an NMR spectrum. Downfield indicates a peak to the left of the spectrum (a weaker applied field). 

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What Is an NMR Spectrum 11.2 Howto Determine Whether an Atomic Nucleus Has... 

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