Projection spectrum

One-dimensional spectra obtained by projecting 2D spectra along a suitable direction often contain information that cannot be obtained directly from a conventional ID spectrum. They therefore provide chemical shift information of individual multiplets that may overlap with other multiplets in the corresponding ID spectra. The main difference between the projection spectrum and the ID spectrum in shift-correlated spectra is that the projection spectrum contains only the signals that are coupled with each other, whereas the ID H-NMR spectrum will display signals for all protons present in the molecule. 

Projection The one-dimensional spectrum produced when one of the two axes of a 2D spectrum is collapsed and the resulting projection spectrum recorded. 

Grant-Muller S (2004) Study of Policies regarding Economic Instruments Complementing Transport Regulation and the Undertaking of physical Measures (SPECTRUM) deliverable 6. The report can be downloaded from http //www.its.leeds.ac.uk/projects/spectrum/downloads/ D6.pdf... 

Use the stored ID spectra as projections and verify the correct calibration of the 2D spectrum. The selected peak(s) in the ID projection spectrum should appear at the same position (ppm) as the corresponding cross peak in the 2D contour spectrum. 

Figure 8 31P 1H) HETCOR spectrum of OCP. For comparison, the H MAS spectrum is appended next to the H projection spectrum. The vertices of the rectangular box correspond to the cross-peaks of monetite (impurity phase). Note that the OCP signal also contributes to the cross-peak at — 0.2 ppm (3,P) and 13.6 ppm ( H). (Reprinted with permission from Ref. 102. 2004 Elsevier.)...

The pulse sequence, as a variant of the spin echo experiment, also refocuses the spread of frequencies caused by field inhomogeneity, so that some improvement in resolution is obtained. The inset at the lower right of Figure 6-18 shows the normal ID spectra of H-4 and H-5 at the top (Figure 6-18c and e) and the unrotated projection of the 2D J-resolved spectra at the bottom [Figure 6-18d and f, extracted from the projected spectrum (Figure 6-18a) at the top of the 2D display]. The much higher resolution of the 2D resonances is clearly evident. Thus, the procedure is an effective way to measure J accurately, particularly when J is poorly resolved in the ID spectrum. The experiment fails for closely coupled nuclei (second-order spectra). 

An A-dimensional NMR spectram is spanned by user-defined sweep widths SW, for each of the N dimensions (i = 1N). For a projection spectrum defined by pi, an appropriate sweep width SW needs to be calculated (Fig. 1). Considering that the distribution of chemical shifts in a given dimension is well described by a normal distribution [39], the sweep width can be calculated as [40]... 

Here, is an Al-dimensional vector containing the transverse relaxation rates along all indirect dimensions, with R 2 = 0 for constant-time evolution elements in the dimension i. Since the standard GAPRO analysis attaches equal weight to each projection spectrum, it is desirable to have similar sensitivities for all individual projection experiments. If the projection angle-dependence of t) is known, (7) provides a basis for producing similar sensitivities for all the projections used in a given APSY experiment, since the user-defined parameters n (p), M (p), hm (p, t), and fmax(0) can be individually adjusted for each projection experiment [5, 42]. 

Figure 5.40. (A) Normal ID spectrum of sucrose (B) J-resolved projection spectrum, showing only singlets instead of multiplets.

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