Nuclear magnetic resonance spectra pulse methods

Fig. 9.—Partial, Proton Nuclear Magnetic Resonance Spectra of 3,4,6-Tri-O-acetyl-l-0-benzoyl-2-chloro-2-deoxy-a-n-glucopyranose in Solution in Degassed Benzene-do. [A. The normal spectrum measured by the Fourier-transform method. B. The spectrum measured with a 3.0-second delay time between the initial, 180°-pulse and the monitoring, 90°-pulse. It should be noted that the resonances of H-5, H-6i, and H-6- have essentially disappeared, leaving the H-2 resonance clearly resolved.]...

A major consequence of the introduction of pulse (FT) NMR spectroscopy has been ready access to C data - limited prior to 1970 by factors which render this magnetic nucleus relatively insensitive to continuous wave methods of recording NMR spectra (1 % natural abundance, and low value of the nuclear magnetic moment compared with that of a proton). C-NMR spectra are generally much simpler than corresponding H spectra. When run under conditions where all couplings to protons are removed (by simultaneous wide-band irradiation of proton resonances), a C-NMR spectrum consists of a series of sharp lines, each of which corresponds to the resonance of a nucleus (or nuclei) of specific magnetic environment. Further, since the chemical shift spread of C nuclei (0-200 ppm) is about 20-times that of protons. 

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