McConnell equation

In physical chemistry, the McConnell equation gives the probability of an unpaired electron in an in aromatic radical compound (such as benzene radical anion $C_{6}H_{6}^{-}$) 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 $$a=Q\rho ,$$ 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

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