Systematic strategy for decoding the NMR spin-spin coupling mechanism: the J-OC-PSP method

Area of Science:

• Nuclear Magnetic Resonance (NMR) Spectroscopy
• Quantum Chemistry
• Computational Chemistry

Background:

• NMR spin-spin coupling is vital for molecular structure determination.
• Current analytical methods for NMR coupling mechanisms have limitations.
• Understanding orbital contributions is key to refining these analyses.

Purpose of the Study:

• To derive new criteria for analyzing NMR spin-spin coupling mechanisms.
• To introduce and detail the J-OC-PSP theory for orbital decomposition.
• To differentiate between through-space and through-bond coupling pathways.

Main Methods:

• Development of the J-OC-PSP (decomposition of J into Orbital Contributions using Orbital Currents and Partial Spin Polarization) theory.
• Orbital decomposition analysis considering one-, two-, and m-orbital effects.
• Analysis of orbital paths, active, passive, and frozen orbitals.

Main Results:

• J-OC-PSP1 decomposes coupling into one- and two-orbital contributions with physical references.
• J-OC-PSP2 clarifies orbital paths and distinguishes through-space from through-bond coupling.
• Fermi contact coupling in hydrocarbons over multiple bonds occurs predominantly through space.

Conclusions:

• The J-OC-PSP method provides a more comprehensive understanding of NMR spin-spin coupling mechanisms.
• Orbital contributions, spin densities, and currents are essential for describing spin transport.
• Through-space interactions are significant for long-range Fermi contact coupling in hydrocarbons.