Carbon coupling constants hydrogen bonding

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

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. 

Figure 5 shows that the best overall description of the coupling constants is obtained with the combination of cc-pVTZ on the doubly bonded carbon atoms, cc-pVDZ on the methyl carbon atom and the minimal basis set on all hydrogens (LDBS apTJ/pT/[pD/m]/m) - the same basis set as for the trans-isorntx. 

The factor ijhb is the bond order between the interacting hydrogen atoms and is unity for H2. Proton-proton bond orders in substituted benzenes as derived from coupling constants and Eq. (21) are given in Table III. The same quantitative significance should not be attached to the proton-proton bond orders of Table III that one gives to the carbon-carbon... 

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