Chemical shift axis

This is easy to understand, if we remember that 1 ppm on the chemical shift axis corresponds to 200,400 and 600 Hz respectively for the three spectrometers. Thus at higher field the multiplet appears compressed . 

The two axes (dimensions) in our 2D spectra are thus both frequency axes. We shall see as we continue that we can adjust our experiment so as to choose different types of frequency information. An early experiment, known as the J-resolved experiment, was designed in such a way that one axis was the (proton or carbon) chemical shift axis and the other the one-bond proton-carbon coupling constant. Flowever, this experiment is not generally very useful for structural determination, so that we shall not discuss it here. 

Fig. 25. One-dimensional slices along the horizontal axis of the 2D FSLG C H HETCOR spectra taken at (a) 4.7 ppm (PG (P) Ha) and (b) 9.3 ppm (PG (P) HN) on the H chemical shift axis.The contact time used in this experiment 1.5, 0.5 and 0.2 ms.

Fig. 30. Line shape analyses of the resonance lines of methine and methyl carbons in sPP/o-dichlorobenzene gel. A, B, and C indicate the crystalline, amorphous, and crystalline-amorphous interfacial components, respectively. (This figure was obtained by revising Fig. 7 in Ref. 25 whose horizontal chemical shift axis was somewhat shifted)...

The F2 frequency normally corresponds to a chemical shift axis, for example, H or l3C. When the Fx axis also corresponds to a chemical shift scale, we describe the result as a... 

HOM2DJ Jh-h 8 H H-H multiplets perpendicular to chemical shift axis... 

Fig. 2 One-dimensional spectrum of ibuprofen (5 mg in 600 pi DMSO-d6> 25°C, 400 MHz). Peak assignments are given above each set of signals. Expansions of the multiplets for the protons attached to C2 and C3 demonstrate the 2nl + 1 rule of scalar coupling. The integral values are given below the chemical shift axis. Note that the peak for the hydroxyl proton at 11.1 ppm is not shown. Small peaks at 3.3, 2.5, and Oppm are from H2O, DMSO-ds, and TMS, respectively.

Figure 10 Schematic representation of nontilted 2D J-resolved experiment. Projection onto the chemical shift axis recovers the high resolution ID NMR spectrum.

Figure 4. homonuclear 2DJ-resolved NMR spectrum of the same glass whose one-dimensional spectrum is shown in Figure 3. The characteristic J coupling pattern is observed for each species. A projection onto the chemical shift axis is shown, above. The projection for each species is designated by the number of phosphorus atoms in the molecule. The lineshape of the octaphosphate was not distinct enough to allow for independent fitting.

Figure 13.3-2. NMR spectra of rat serum illustrating the various NMR responses that are possible through the use of different pulse sequences, which edit the spectral intensities (a) standard water suppressed spectrum, showing all metabolites (b) CPMG spin-echo spectrum, with attenuation of peaks from fast relaxing components such as macromolecules and lipoproteins (c) diffusion-edited spectrum, with attenuation of peaks from fast diffusing components such as small molecules and (d) a projection of a 2D J-resolved spectrum on to the chemical shift axis, showing removal of all spin-spin coupling and peaks from fast relaxing species.

Chemicai shift axis. The scale used to calibrate the abscissa (x-axis) of an NMR spectrum. In a one-dimensional spectrum, the chemical shift axis typically appears underneath an NMR frequency spectrum when the units are given in parts-per-millions (as opposed to Hz, in which case the axis would be termed the freguency axis). 

All 1-D NMR time domain data sets must undergo one Fourier transformation to become an NMR spectrum. The Fourier transformation converts amplitude as a function of time to amplitude as a function of frequency. Therefore the spectrum shows amplitude along a frequency axis that is normally the chemical shift axis. 

Cross peak. The spectral feature in a multidimensional NMR spectrum that indicates a correlation between a frequency position on one axis with a frequency position on another axis. Most frequently, the presence of a cross peak in a 2-D spectrum shows that a resonance on one chemical shift axis somehow interacts with a different resonance on the other chemical shift axis. In a homonuclear... 

What we are still missing is how the second dimension—the chemical shift axis—is introduced. 

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