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In physical chemistry, the McConnell equation gives the probability of an unpaired electron in an in aromatic radical compound (such as benzene radical anion ${\displaystyle C_{6}H_{6}^{-}}$) being on a particular atom. It relates this probability, known as the "spin density", to its proportional dependence on the hyperfine splitting constant.

The equation is $${\displaystyle a=Q\rho ,}$$ where ${\textstyle a}$ is the hyperfine splitting constant, ${\textstyle \rho }$ is the spin density, and ${\textstyle Q}$ is an empirical constant that can range from 2.0 to 2.5 mT.

History

The equation is named after Harden M. McConnell of Stanford University, who first presented it in 1956.

References

1. McConell, H. M. (1956). "Indirect Hyperfine Interactions in the Paramagnetic Resonance Spectra of Aromatic Free Radicals". Journal of Chemical Physics. 24: 764–766. doi:10.1063/1.1742605.

• Atkins, Peter; de Paula, Julio. Atkins' Physical Chemistry (9th ed.). Oxford University Press.

• Chemical physics