Shift correlation spectroscopy

Heteronuclear chemical shift-correlated spectroscopy, commonly called H-X COSY or HETCOR has, as the name implies, different and F frequencies. The experiment uses polarization transfer from the nuclei to the C or X nuclei which increases the SNR. Additionally, the repetition rate can be set to 1—3 of the rather than the longer C. Using the standard C COSY, the ampHtude of the C signals are modulated by the... 

A more useful type of 2D NMR spectroscopy is shift-correlated spectroscopy (COSY), in which both axes describe the chemical shifts of the coupled nuclei, and the cross-peaks obtained tell us which nuclei are coupled to which other nuclei. The coupled nuclei may be of the same type—e.g., protons coupled to protons, as in homonuclear 2D shift-correlated experiments—or of different types—e.g., protons coupled to C nuclei, as in heteronuclear 2D shift-correlated spectroscopy. Thus, in contrast to /-resolved spectroscopy, in which the nuclei were being modulated (i.e., undergoing... 

Homonuclear shift-correlation spectroscopy (COSY) is a standard method for establishing proton coupling networks. Diagonal and off-diagonal peaks appear with respect to the two frequency dimensions. 

Heteronuclear correlation spectroscopy (HETCOR) Shift-correlation spectroscopy in which the chemical shifts of different types of nuclei (e.g., H and C) are correlated through their mutual spin-coupling effects. These correlations may be over one bond or over several bonds. 

Heteronudear shift correlation spectroscopy is a 2D technique that can be used to determine the connectivity of H and C nuclei (or other heteronuclei), formally bonded together through one or more chemical bonds. The corresponding experiments make use of either the large or the smaller long-range "Jv, couplings for polarization transfer. 

The most recent developments in 2D NMR of solids are the heteronuclear chemical shift correlation spectroscopy (421), 2D exchange NMR, which enables very slow molecular reorientations to be monitored (422), and heteronuclear. /-resolved 2D NMR (423). 

Signal assignment in routine NMR spectroscopy is usually facilitated by the application of two-dimensional assignment techniques such as homonuclear proton-proton shift correlated spectroscopy ( H/ H-COSY). 

Although we might be able to get all the H-H coupling information through a long series of homonuclear decoupling experiments, there is a much simpler way the 2D NMR technique known as homonuclear shift correlation spectroscopy, or COSY. 

So far we have discussed homonuclear 2D H,H-shift correlation spectroscopy (H,H-COSY) as well as heteronuclear 2D C,H-shift correlation spectroscopy (C,H-COSY, or C,H-HSC). Let us now consider homonuclear 2D C,C-shift correlation spectroscopy. 

Laurie was one of the first to apply two-dimensional (2D) NMR to carbohydrates. With students Subramaniam Sukumar and Michael Bernstein, and visiting scientist Gareth Morris, he demonstrated and extended the application of many of the directly observed 2D NMR techniques of the time. These included the homo- and hetero-nuclear 2D /-resolved techniques, delayed proton /-resolved NMR that allowed broad resonances to be suppressed, for example, those of dextran in the presence of methyl /Lxvlopyranoside. proton-proton chemical shift correlation spectroscopy (COSY), nuclear Overhauser enhancement spectroscopy (NOESY), proton-carbon chemical shift correlation (known later as HETCOR), and spin-echo correlated spectroscopy (SECSY). Trideuteriomethyl 2,3,4,6-tetrakis-<9-trideuterioacetyl-a-D-glucopyranoside served as a commonly used model compound for these studies. 

The field of long-range 2D heteronuclear shift correlation spectroscopy at... 

Bilia et al. reported the efficiency of two-dimensional homonuclear H- H correlated spectroscopy and two-dimensional reverse heteronuclear shift correlation spectroscopy in evaluating the composition of phloroglucinols, flavonols and naphthodianthrones in a dried extract of St John s wort. They successfully assigned carbon resonances for these three classes of compounds and also identified shikimic and chlorogenic acids, sucrose, lipid, polyphenols and traces of solvent (methanol) during the extraction process. This rapid technique is an alternative to HPLC, TLC or capillary GC for the analysis of St John s wort preparations. Another report utilized near-infrared reflectance spectroscopy (NIRS) for the... 

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