Correlated spectral dispersion

HETCOR and COLOC involve C detection these have been superseded by more sensitive Undetected HMQC, HSQC, and HMBC experiments, which provide ca. 30-fold sensitivity improvement over C detection. Heteronuclear correlation experiments provide simpler spectra (a single peak is observed for each C-H attachment) and they take advantage of the much greater C spectral dispersion. 

Finally, when studying dilute solutions of high-molecular-weight flexible coil macromolecules, an additional contribution to the spectral dispersion of the scattered light can arise from the dynamic behavior of the low frequency, long wavelength internal vibrational motions of the chains (70). Additional Lorentzian spectral components (or exponential components of the correlation function) arise through this mechanism characterized by halfwidth (time constant) ... 

Triple resonance 3D-NMR experiments can be useful for studying polymeric structures without resorting to isotopic labeling, even when the nuclei involved are present in low natural abundance. This study of MD3M shows that the considerable spectral dispersion obtained in the Si NMR spectra of siloxanes, compared with the narrow H and C chemical shift ranges, permits detailed examination of the structure of PDMS by the 3D H/ C/ Si NMR correlation experiment. These techniques can also be usefiil for characterizing star-branched polymers which contain NMR active nuclei, polymers with low concentrations of heteroatoms (e.g. at the chain end or at low occurrence branch points) and many organometallic compounds. 

There are basically two types of 2D NMR experiments. These are termed (1) resolved and (2) correlated, according to the type of dispersion in the second frequency dimension oj. Resolved experiments are a way of improving spectral dispersion... 

To investigate spectral sensitivity, samples were exposed to spectrally dispersed irradiation [6]. Thus, sample position correlates with the irradiation wavelength. By measuring spectral irradiance as well as property change, spatially resolved, spectral sensitivity can be calculated. For uncoloured PP, the failure by crack formation was quantified as crack formation probability w t) which was correlated to nearsurface carbonyl formation. ... 

Part of the power of 2D NMR comes from its ability to provide tremendous spectral dispersion however, the structural information present from the correlation of frequencies is equally important. Organic chemists have been performing elegant syntheses for... 

In benzene solvent, 89 had h and resonances that were very well dispersed compared to the resonances in the spectra obtained in chloroform. Therefore, in benzene, the HMQC-TOCSY 2D-NMR experiment gave sufficient spectral dispersion. The NH2 protons are not seen in either of the HMQC-TOCSY experiments because it has no scalar couplings to the rest of the molecule. The NH2 protons however do show NOESY correlations with some protons... 

The radial velocities have been computed with the low resolution set-up (more spectral lines, no telluric line), using a cross-correlation technique. When excluding the seven outliers, the peak in centered at 83.0 0.4kms 1 with a dispersion of 1.9 0.2kms 1. Lithium abundance is being determined using Li i 6707.8 A. We used the B — V index to determined the ([3]), and the curve of growth from [7] to derive AT(Li). 

As an example of a more dispersed system, H 2Q- and 3Q-HoMQC spectra of the cyclic antibiotic primycin [30] recorded at 800 MHz [31] are shown in fig. 6. This molecule has a sequence of alternating CH(OR) and CH2 groups, establishing correlations both within, and between the two extreme regions of the spectrum. The spectral windows could be still chosen to be equal with no serious overlap introduced on the final spectrum. 

Due to limitations in signal-to-noise ratio available for the then common dispersive IR instruments, peptide and protein vibrational spectroscopic studies shifted to emphasize Raman measurements in the 1970s 29-32 Qualitatively the same sorts of empirical correlations as discussed above have been found between frequencies of amide bands in the Raman and secondary structure. However, due to the complementary selection rules for Raman as compared to IR and to the multi-component nature of these polymeric spectral bands, the... 

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