Static and dynamic spin
polarization effects are distinguished. The static
polarization of an electron spin occurs in the
C–
H
bonds of aromatic radicals where the σ-electron closest to an unpaired π-electron
tends to have its spin parallel to that of the π-electron. Likewise, static spin
polarization arises in the π-system of conjugated radicals: the electron of the doubly occupied
molecular orbital prefers to take a closer spatial position to the odd one, which spin is parallel
to the latter. The effect reflects the energy unfavourable situation if an electron
of opposite spin were to come nearby.
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