Proton long range

As shown above, one must first determine the carbon to which the proton long-range correlations are observed. Referring to a GHMBC spectrum will, of course, provide insight into which carbons are... 

Two-dimensional carbon-proton shift correlation via long-range CH coupling... 

Two-dimensional C//correlations such as C//COSY or HC HMQC and HSQC provide the Jqh connectivities, and thereby apply only to those C atoms which are linked to H and not to non-protonated C atoms. Modifications of these techniques, also applicable to quaternary C atoms, are those which are adjusted to the smaller Jqh and Jqh couplings (2-25 Hz, Tables 2.8 and 2.9) Experiments that probe these couplings include the CH COLOC (correlation via long range couplings) with carbon-13 detection (Fig. 2.16) and HC HMBC (heteronuclear multiple bond coherence) with the much more sensitive proton detection (Fig. 2.17)... 

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... 

Note the relationship between Ha and the other hydrogens. Long-range coupling to Ha (J 4 Hz) is observed in only one of these molecules. Which molecule do you think this is Identify the proton that is coupled to Ha. 

As must be expeeted for all these studies of long-range interaetions, large basis sets with diffuse funetions in eombination with eorrelation methods (at least MP2) are mandatory. DFT ealeulations were performed in order to determine the preferred addition site of OH to protonated 4-ethylimidazole [99JPC(A)1283]. As supported by eomputed hyperfine eoupling eonstants, the OH radieal adds... 

The widespread occurrence of long-range couplings in both furanose and pyranose derivatives explains why so many of the P.M.R. spectra of carbohydrate derivatives are apparently poorly resolved, even when the resolution of the spectrometer is above reproach. For example, the Hi resonance of the 1,6-anhydro-D-glucose derivative (12) is coupled to all of the other six ring protons. A further example of the line-broadening effect follows a consideration of the spectrum of 5,6-dideoxy-5,6-epithio-l,2-0-isopropylidene-/ -L-idofuranose for which the half-height... 

Long-range coupling between protons more than two carbon atoms apart is sometimes observed when v bonds intervene. An example is found in l-methoxy-l-buten-3-yne. Not only does the acetylenic proton, Ha, couple with the vinylic proton H, it also couples with the vinylic proton Hc, four carbon atoms away. The data are ... 

A long-range proton coupling, which was found to be transmitted by a sulfone group in thiolane dioxide systems292, is apparently facilitated by a nonbonding p-orbital on one of the sulfone oxygen atoms. This phenomenon is of interest for saturated cyclic systems. 

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