conserved, which means that the radical-pair now formed is a singlet (each electron has opposite spin, as in the origin bond). As such, the reverse reaction, i.e. the reforming of a bond, called recombination, readily occurs. The radical-pair mechanism explains how external magnetic fields can prevent radical-pair recombination with Zeeman interactions, the interaction between spin and an external magnetic field, and shows how a higher occurrence of the triplet state accelerates radical reactions because triplets can proceed only to products, and singlets are in equilibrium with the reactants as well as with the products. Zeeman interactions can “flip” only one of the radical's electron's spin if the radical-pair is anisotropic, thereby converting singlet radical-pairs to triplets. The Zeeman interaction is an interaction between spin and external magnetic field, and is given by the equation where is the energy of the Zeeman interaction, is the Larmor frequency, is the external magnetic field, is the Bohr magneton, is Planck's constant, and is the g-factor of a free electron, 2.002319, which is slightly different in different radicals. It is common to see the Zeeman interaction formulated in other ways. Hyperfine interactions Hyperfine interactions, the internal magnetic fields of local magnetic isotopes, play a significant role as well in the spin dynamics of radical-pairs. Zeeman interactions and magnetoreception Because the Zeeman interaction is a function of magnetic field and Larmor frequency, it can be obstructed or amplified by altering the external magnetic or the Larmor frequency with experimental instruments that generate oscillating fields. It has been observed that migratory birds lose their navigational abilities in such conditions where the Zeeman interaction is obstructed in radical-pairs. External links Spin chemistry portal References Physical chemistry Nuclear magnetic resonance