Homonuclear shift-correlation spectroscopy

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. 

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. 

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... 

Another 2D homonuclear shift-correlation experiment that provides the coupling information in a different format is known as SECSY (spin-echo correlation spectroscopy). It is of particular use when the coupled nuclei lie in a narrow chemical shift range and nuclei with large chemical shift differences are not coupled to one another. The experiment differs... 

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). 

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. 

Because, in (RSn)i20i4(OH)6 X2, the anions do not interact directly with any tin atom but with the /U-2-OH that constitute the charged poles, the exchange of the anions or their ionic dissociation cause only small changes on the Sn chemical shifts (Table 2.3.1). H- H NOESY/ROESY (homonuclear Overhauser correlation spectroscopy) and HOESY (heteronuclear NOESY) have been used to... 

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... 

H-NMR analysis allows the elucidation of GSL structures, without the use of destructive methods and requires small amounts (nmole) of material. In addition to one dimensional 1 H-NMR, other methods such as two-dimensional 1H-NMR shift correlations spectroscopy (COSY), two-dimensional nuclear Overhauser 1 H-NMR spectroscopy (NOESY) and homonuclear two-dimensional spin-echo J-resolved 1 H-NMR spectroscopy. The introduction of1 C-NMR into the field of glycosphingolipid research should give useful information on the stereochemical conformation of molecules. This is of coniderable interest, as they most probably contribute to the immunological specificity of glycosphingolipids (37). 

In a study of the biosynthesis of riboflavin from [U- Cjglucose, application of C-homonuclear J-spectroscopy and 2D-chemical shift correlation spectroscopy, as well as 2D-INADEQUATE techniques, were... 

Figure. 5.62. Alternative pulse sequence for homonuclear 2D-shift correlated spectroscopy. The two pulsed field gradients, FG, are applied to suppress axial peaks and to distinguish between positive (P) and negative (N) peaks.

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