by Nikolai V. Shokhirev
Prof. F. Ann Walker Research Group, Department of Chemistry, University of Arizona, Tucson, Arizona 85721, USA
The Curie factors are the most unambiguous quantities. The only assumption is that the molecule (complex) has the same diamagnetic shifts for both ground and excited states. The Curie factors can be directly connected with the total paramagnetic shifts and the effective hyperfine constant.
The paramagnetic shift can be further divided into the dipole-dipole contribution and the Fermi contact term. The corresponding HFI constants are
respectively. Here is the fraction of the unpaired electron (spin density) at the atom (nucleus) N.
The dipole constant is derived under of assumption of point dipoles interaction. Usually it is also assumed that Add is the same for the ground and excited state.
The contact shifts accumulated all previous assumptions. However they are directly connected with the electronic structure via the spin densities. Usually the proton shifts are measured. However it is easier to calculate the spin density at the adjacent carbon atoms. To connect them the McConnell empiric relation is used
Remark. All chemical shifts are dimensionless. All HFI constants have dimension of energy.
©Nikolai V. Shokhirev, F. Ann Walker, 2002