Static and dynamic spin @P04712@ effects are distinguished. The static @P04712@ 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 @P04712@ arises in the π-system of conjugated radicals: the electron of the doubly occupied @M03996@ 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.