Analysis of the spin-dipole transmission mechanism for NMR spin–spin coupling constants using orbital contributions, spin polarization, and spin-dipole energy density distribution

For the analysis of the spin-dipole (SD) term of the indirect NMR spin–spin coupling constant, the SD spin-polarization distribution and the SD energy density distribution are derived and used to explain magnitude and sign of the SD term. Orbital pairs (occupied, virtual) are identified that are most important for the SD spin–spin coupling mechanism. The induction of strong SD spin-polarization requires low excitation energies and complementing nodal properties of zeroth and first-order orbitals. The SD components for 1J(CC) of typical CC bonds are analyzed. The SD term is a sensitive antenna for detecting the π-character of a bond.