Hydrogen bonds coupling constant

Table 7.56 One-Bond Carbon-Hydrogen Spin Coupling Constants 7.107...

Exocyclic conjugation causes a small upheld shift of the ring hydrogen resonances, as can be seen in Table 6. The increase in tr-bond hxation also results in an increase in the 4,5 coupling constant to about 6.0 Hz. The use of coupling constants for the investigation of tautomerism is discussed in Section 4.17.5. 

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. 

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