Hydrogen direct coupling constants, carbon

Take note that this effect would stabilize the equatorial anomers, hence diminishes the anomeric effect of oxygenated substituents. However, there are other physical indications of the favoured delocalization of the cyclic oxygen towards the exocyclic oxygen as furnished by the direct coupling constant value Vch between the anomeric carbon and hydrogen. A comparison of the 7ch values, measured on about 20 anomeric pairs having various configurations and substitutions, shows that for each pair we observe... 

Spin densities help to predict the observed coupling constants in electron spin resonance (ESR) spectroscopy. From spin density plots you can predict a direct relationship between the spin density on a carbon atom and the coupling constant associated with an adjacent hydrogen. 

Again, we need to define a coupling constant J to set up this experiment. Here for optimum sensitivity we have used an average value for direct (one-bond) carbon-hydrogen coupling constants of 160 Hz. This choice works well for most CH bonds, but is rather low if an acetylenic CH bond is present. 

Similar spectra can be obtained more rapidly and with less sample if the data are acquired through the proton signals, which are much more intense. Basically, the H NMR data are acquired and the H- C coupling constant used as the delay in a pulse sequence, which enables us to obtain the carbon spectrum. This method of obtaining the data is called inverse-mode , since the carbon atoms are detected through their attached hydrogen atoms rather than by direct detection, with obvious benefits in the sensitivity and the time taken to obtain a spectrum. HMQC and HMBC are both examples of inverse-mode spectra and this method is so much quicker than CH COSY that an entire HMQC spectrum can be obtained in much less time than it takes to obtain the proton-decoupled C... 

C. Direct Carbon-Hydrogen and Carbon-Fluorine Coupling Constants References... 

Table II. Chemical Shifts and Directly Bonded Carbon-Hydrogen Coupling Constants for C-2 Carbon in Imidazole Derivatives °...

The calculated values are reported in Table IV. The quantity p has been related (19) to the direct carbon-13 hydrogen coupling constant by a well-known relationship ... 

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