2JCh couplings

Figure 19 Schematic effect of the STAR operator on 2JCH and 3,/CH couplings. The vicinal component of magnetization in the long-range response that is two-bond coupled to a protonated carbon experiences modulation, which serves as a pseudo-evolution for this coupling. In contrast, the vicinal component of magnetization in the long-range response that is three-bond coupled to a protonated carbon does not exhibit a F, skew. Homonuclear modulation during the evolution period f, is still present, as the full experiment is not a constant-time experiment.

Table 3.9. Two Bond Coupling Constants 2JCH of Selected Alkyl, Alkenyl, and Alkynyl Compounds. ...

When an oxygen is synclinal to a C —C —H coupling path, 2JCH is negative, while an antiperiplanar configuration causes geminal coupling to be positive [129] ... 

Table 2.7. Structural features and geminal (two-bond) CH coupling constants 2JCh (Hz) 4-6,16...

Two-dimensional CH correlations such as CH COSY or HC HMQC and HSQC provide the JCh 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 2JCh and 5JCh couplings (2-25 Hz, Tables 2.8 and 2.9) l6,23. Experiments that probe these couplings include the CH COLOC 24 (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)17. 

Figure 63. The HMQC sequence and associated coherence transfer pathway. The A periods are set to 1 /2Jch to enable to defocusing and subsequent refocusing of the one-bond heteronuclear coupling.

Hz in 3JHIJ(trans), 0.43 Hz in 1JCh, -0.67 Hz in 2JCh, and 0.07 Hz in lJCc) The data in Table 5 also show good agreement between our results and post-HF results for the DSO term. The calculation of the DSO contribution is clearly not a bottleneck of our approach. Our calculations confirm the conclusion [113] about the importance of the DSO contribution to the nuclear spin-spin coupling constants. 

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