Proton-carbon three-bond

Bonded to adjacent carbons three bonds between protons... 

In the selective INEPT technique (ref. 5), the proton is irradiated with a soft pulse and the dwell time prior to observation is varied depending on the anticipated (or preferably known) coupling constant. Typically, the experiment is utilized for the selective enhancement of carbons three bonds away from the irradiated proton where J values in the range 6-8 Hz are used. There are two important exceptions to this range of J. values. In the case of... 

CH COLOC Correlation via long-range CH coupling, detects CH connectivities through two or three (more in a few cases) bonds in the CH COSY format, permits localisation of carbon nuclei two or three bonds apart from an individual proton... 

Hexafluoro-wo-propanol has become a popular solvent. Its fluorine, proton, and carbon spectra are provided in Figs. 6.15-6.17. The doublet in the fluorine spectrum centered at -77.1 ppm exhibits a three-bond... 

HMBC //eteronuclear multiple frond correlation. A proton-detected, two-dimensional technique that correlates protons to carbons that are two and three bonds distant. Essentially, it is an HMQC that is tuned to detect smaller couplings of around 10 Hz. 

The 5 Hz optimized l,n-ADEQUATE spectrum of strychnine (1) is shown in Figure 9.70 The high resolution 600 MHz proton spectrum is shown in Figure 10A and compared to slices extracted at the Fi frequency of the C15 methylene resonance in the 5 Hz optimized l,n-ADEQUATE spectrum (B) and the 60 Hz optimized 1,1-ADEQUATE spectrum (C). The adjacent carbons (via Vcc) show correlations in the 5 Hz optimized INADEQUATE spectrum that are unsuppressed but all possible three-bond... 

It is interesting to note from even the examination of just the three carbon-carbon correlation pathways from Cl 4, that there is no uniformity in the Jch correlations observed to C14 from the various protons among these correlations. Further, while the observed "/ch correlations are predominantly three-bond correlations, a weak two-bond correlation from H13 to C14 was among the correlations observed. Hence, the h,1-ADEQUATE experiment suffers from the same potential ambiguities of the correlation pathways as the GHMBC experiment. 

Figure 19 Schematic effect of the STAR operator on 2JCH and 3,/CH couplings. The vicinal component of magnetization in the long-range response that is two-bond coupled to a protonated carbon experiences modulation, which serves as a pseudo-evolution for this coupling. In contrast, the vicinal component of magnetization in the long-range response that is three-bond coupled to a protonated carbon does not exhibit a F, skew. Homonuclear modulation during the evolution period f, is still present, as the full experiment is not a constant-time experiment.

Conformational analysis of oligosaccharides in solution by NMR spectroscopy is based on the study of chemical shifts, n.O.e. s, and three-bond, proton-carbon coupling constants. Generally, the experimental NMR parameters P. . , (such as n.O.e. s or... 

Until now, the determination of three-dimensional structures of oligosaccharides in solution was based primarily on proton-proton distance information obtained from n.O.e. data. Here, we discuss the application of three-bond proton-carbon coupling constants. 

Three-Bond Proton-Carbon Coupling Constants. Routine applications of the three-bond C-O-C-H proton-carbon coupling constants ( Jpu) have been coiqplicated by experimental difficulties involved in tneir measurement using classical H-coupled NMR spectroscopy and a limited knowledge of the angular dependence of for the C-O-C-H... 

The teirperature dependencies of the chemical shift values for both Cl and C4 were determined in four different solvents (water, dimethyl sulfoxide, methanol and dioxane) and are shown in Figures 8 and 9. The resonance for Cl at 298 C varied from 101.6 ppm in D2O to 104.0 ppm in methanol. The resonance for C4 at the same temperature varied from 75.3 ppm in dimethyl sulfoxide to 78.3 ppm in methanol. The most pronounced tenperature dependence is observed in water and dioxane, where Cl and C4 signals varied from 101.4 ppm to 101.9 ppm (Cl, water, 278-358 K) and from 75.7 ppm to 76.5 ppm (C4, dioxane, 288-360 K), respectively. Thus, both tenperature and solvent dependence of C shifts indicate different conformational behavior of the molecule at various physico-chemico conditions. This feature is manifested even more clearly by the dependencies of the three-bond proton-carbon J and J coupling constants (< ) - Hl -Cl -04-C4 and f = H4-C4-04-C1 ) which are plotted against tenperature in Figures 10 and 11. 

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