Carbon-Proton Coupling

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... 

A. Biopolvmers, in press). Having five different proton-carbon couplings for each of the conformers, 75 couplings were calculated and those are plotted together with the calculated angular dependence in Figure 6. 

Organophosphorus compounds rarely have more than one P atom in the molecule, giving rise to a doublet for any C atom within three bonds (assuming the proton-carbon coupling has been removed) and so these compounds show clearly the connectivity of carbon atoms close to the P atom. The size of the coupling constant is dependent on the number of bonds and the phosphorus oxidation state, such that Vis the largest at about 45-150 Hz, while V and V are of the order of 10-15 Hz. 

It has been proved by X-ray analysis that, in the solid state, 1 is the tautomer present, but the claim has been made that,68 in solution, L-ascorbic acid exists as 2. Structures 3,4, and 5 were readily eliminated by a study of the l3C-n.m.r. spectrum,88,87 and, on the basis of the chemical shifts of the carbon resonances for C-l, C-2, and C-3, and the known chemistry of L-ascorbic acid, 1 is favored over 2 in solution. Berger98 claimed that the proton-carbon-coupled spectrum of L-ascorbic acid is consistent only with structure 1. Ogawa and coworkers87 studied the conformation of L-ascorbic acid and L-ascorbic acid-5-d in deuterium oxide by 13C-n.m.r. spectroscopy, and concluded that, in... 

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). 

A number of natural product studies reported in 2003 also utilized cryoprobe technology. Among the studies reported, Griesinger et al 56 addressed the measurement of long-range proton-carbon couplings in natural products in orienting media. 

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