Spin-coupling rules of ground state have been studied for a series of organic biradicals using quantum-chemical ab initio UHF methods. It is further proved that there are topological rules of ferromagnetic coupling between radicals in cojugated systems. Several explanations about redical coupling have been unified in order to provide theoretical guide for experimental synthesis of magnetic materials.

Key words: COUPLING, AB INITIO CALCULATION, MAGNETISM, FERROMAGNETISM, FREE RADICALS