2D-Homonuclear shift correlated

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... 

Figure 5.69. 2D-Homonuclear shift correlated H-NMR spectrum of nigellicine, a new alkaloid isolated from Nigella sativa ( kalonji ). The circles on the diagonal line correspond to the peaks of the H-NMR shown on the horizontal axis but give a view of them from above. The cross peaks above and below the diagonal establish the connectivities between a and c / d .

Figure 5.70. 2D-Homonuclear shift correlated H-NMR spectrum of 795-vindolinine. The cross peaks establish the connectivities between the protons.

Some of the most important 2D experiments involve chemical shift correlations between either the same type of nuclei (e.g., H/ H homonu-clear shift correlation) or between nuclei of different types (e.g., H/ C heteronuclear shift correlation). Such experiments depend on the modulation of the nucleus under observation by the chemical shift frequency of other nuclei. Thus, if H nuclei are being observed and they are being modulated by the chemical shifts of other H nuclei in the molecule, then homonuclear shift correlation spectra are obtained. In contrast, if C nuclei are being modulated by H chemical shift frequencies, then heteronuclear shift correlation spectra result. One way to accomplish such modulation is by transfer of polarization from one nucleus to the other nucleus. Thus the magnitude and sign of the polarization of one nucleus are modulated at its chemical shift frequency, and its polarization transferred to another nucleus, before being recorded in the form of a 2D spectrum. Such polarization between nuclei can be accomplished by the simultaneous appli-... 

In homonuclear-shift-correlated experiments, the Ft domain corresponds to the nucleus under observation in heteronuclear-shift-correlated experiments. Ft relates to the unobserved or decoupled nucleus. It is therefore necessary to set the spectral width SW, after considering the ID spectrum of the nucleus corresponding to the Ft domain. In 2D /-resolved spectra, the value of SW depends on the magnitude of the coupling constants and the type of experiment. In both homonuclear and heteronuclear experiments, the size of the largest multiplet structure, in hertz, determines... 

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. 

HOM2DJ, 2D homonuclear 7-resolved experiment HSC, 2D heteronuclear shift correlation Hz, unit of frequency (cycles per second)... 

D Correlated NMR Homonuclear Shift Correlation Jeener Two-pulse Expt. H h.Jhh h.Jhh 3,50,52 3,49-52... 

Two-dimensional covariance NMR spectroscopy, which was originally established to extract homonuclear correlations (HOMCOR), has been extended to include heteronuclear correlations (HETCOR) by Takeda et al. In a 2D chemical shift correlation experiment, and N... 

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... 

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