One-bond proton—carbon 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. 

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

S. Uhrinova, D. Uhrin, T. Liptaj, J. Bella, J. Hirsch, Measurement of one-bond proton-carbon coupling constants of saccharides, Magn. Reson. Chem. 29 (1991) 912-922. 

For the HMQC described above, we wanted an experiment that eliminated long-range (i.e., two and three bond) proton-carbon couplings while preserving the directly attached (i.e., one-bond) couplings, which we correlated in a 2-D experiment. The HMBC (Heteronuclear Multiple Bond Coherence) experiment, on the other hand, which is also proton detected, capitalizes... 

T.N. Pham, T. Liptaj, K. Bromek, D. Uhrin, Measmement of small one-bond proton-carbon residual dipolar coupling constants in partially oriented C natmal abundance oligosaccharide samples. Analysis of heteronuclear JcH-modulated spectra with the BIRD inversion pulse, J. Magn. Reson. 157 (2002) 200—209. 

H and 13C NMR Data. Pertinent proton and carbon NMR data, in addition to those given above, are provided in Scheme 3.9. Again, the increase in one-bond F—C coupling constant observed in the... 

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. 

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