Heteronuclear shift-correlation spectroscopy

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... 

A number of papers have looked at the development of relationships between base stock composition as measured by NMR and either physi-cal/chemical properties or their performance.22 27 Most of this work has been focused on group II and III base stocks, with less or little attention paid to solvent extracted ones. These have all relied on various techniques to simplify the spectra and the assignments of peaks and make peak integration more reliable. These have many acronyms,23 for example, GASPE (gates spin echo), PCSE (proton coupled spin echo), INEPT (insensitive nuclei enhancement by polarization transfer), DEPT (distortionless enhancement by polarization), QUAT (quaternary-only carbon spectra), 2D COSY (two-dimensional homo-nuclear spectroscopy), and HETCOR (heteronuclear shift correlated spectroscopy)]. Table 4.10 provides an example of some of the chemical shift data generated26 and employed in this type of work, and Adhvaryu et al.25 were able to develop the correlations between base stock properties and carbon types in Table 4.11, whose main features correspond to intuition (e.g., the values of API and aniline points are both decreased by aromatic carbon and increased 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 shift-correlated spectroscopy. Thus, in contrast to /-resolved spectroscopy, in which the nuclei were being modulated (i.e., undergoing... 

T.T. Nakashima, B.K. John and R.E.D. McClung, Selective 2D DEPT heteronuclear shift correlation spectroscopy, J. Magn. Resonance 59, 124 (1984) and references therein. 

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