by Nikolai V. Shokhirev

Prof. F. Ann Walker
Research Group,
Department of Chemistry,
University of Arizona,
Tucson, Arizona 85721, USA

### Interpretation of Curie factors

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

and

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 *A*_{dd} 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