Coupling constants proton-carbon

The two axes (dimensions) in our 2D spectra are thus both frequency axes. We shall see as we continue that we can adjust our experiment so as to choose different types of frequency information. An early experiment, known as the J-resolved experiment, was designed in such a way that one axis was the (proton or carbon) chemical shift axis and the other the one-bond proton-carbon coupling constant. Flowever, this experiment is not generally very useful for structural determination, so that we shall not discuss it here. 

T. Parella, 2D methods for the measurement of long-range proton-carbon coupling constants, in Multidimensional NMR Methods for the Solution State, G. A. Morris and J. W. Emsley (eds.), John Wiley Sons Ltd, Chichester, 2010, pp. 305-314. 

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... 

Vicinal proton-carbon coupling constants in a series of conformationally rigid monosaccharide derivatives showed a satisfactory dependence of upon the torsion angles (2). The... 

Vicinal Proton-Carbon Coupling Constants for Glycosides... 

Improved sensitivity of NMR instruments has enabled the development of methods for the measurement of carbon-carbon coupling constants, particularly the long-range coupling constants, which are expected to complement the proton-proton and proton-carbon coupling constants in the configurational and conformational analysis of compounds. 

Since the NMR resonances of chemically different protons are more widely separated at higher field, X3C-NMR spectra measured without proton decoupling will have more clearly defined multiplets, and as a result the magnitudes of proton-carbon coupling constants will be more easily extracted. A good illustration of this aspect is the proton-coupled spectra of propene recorded at 25 and 101 MHz discussed by Dubs and von Phil-ipsbom (7). 

I. Tvaroska, M. Hricovmi, and E. Petrakova, An attempt to derive a new Karplus-type equation of vicinal proton-carbon coupling constants for C-O-C-H segments of bonded atoms, Carbohydr. Res., 189 (1989) 359-362. 

T. Nishida, G. Widmalm, and P. Sandor, Hadamard long-range proton-carbon coupling constant measurements with band-selective proton decoupling, Magn. Reson. Chem., 33 (1995) 596-599. 

The availability of 13C-labeled carbohydrates has allowed the use of 3D NMR experiments for the measurement of both proton-proton and proton-carbon coupling constants.10,63,64... 

Vicinal proton-carbon coupling constants (3.7h65,C4 and J is.v.ci) also provide valuable information about the hydroxymethyl conformation. Theoretical calculations were applied to establish Karplus-type equations that correlate these couplings with lu torsion angle and then these were used to estimate C5—C6 rotamer... 

Figure 4.11. The application of selective proton decoupling in the measurement of heteronuclear long-range proton-carbon coupling constants. Lower traces are from the fully proton-coupled carbon-13 spectrum and the upper traces from that in which the methyl ester protons of 4.3 were selectively decoupled to reveal the three-bond coupling of the carbonyl carbon across the alkene.

Table 4.2. Typically ranges for one-bond proton-carbon coupling constants...

Figure 7.4. Heteronuclear /-resolved sequences for the measurement of long-range proton-carbon coupling constants (a) semi-selective,...

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