Spin–Spin Coupling between Geminal and Vicinal Protons

The geminal (HCH) and vicinal (HCCH) proton spin–spin coupling constants are of fundamental importance in the applications of nuclear magnetic resonance (NMR) spectroscopy in structural and conformational analysis, since they are extremely sensitive to fine details of steric and electronic molecular structure. The nature of the dependence of the constants on individual structural factors (bond length, valence and dihedral angles, electronic structure of the substituents and their orientation, etc.) has been examined in detail. At present a priori theoretical calculations do not allow an exact description of these relations and therefore a semiempirical approach, based on general qualitative relations found by quantum-mechanical calculations, is very promising.
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