Electron Spin Resonance Studies of Coals and Coal - Derived Asphaltenes

The d iscovery o f e l e c t r o n s p i n resonance ( e s r ) absorp t ion i n n a t u r a l carbons by Uebersfeld (1) and Ingram ( 2 ) prompted a number of i n v e s t i g a t o r s to apply t h e techn ique t o coa l and materials der ived from c o a l . A t least t h r e e e x c e l l e n t review a r t i c l e s descr ib ing t h e e a r l y esr s t u d i e s o f c o a l s have been published ( 3 5 ) . A l though t h e e x a c t n a t u r e of t h e s p e c i e s r e s p o n s i b l e f o r t h e esr absorp t ion h a s not been e s t a b l i s h e d unambiguously, i t i s g e n e r a l l y thought t h a t t h e unpaired e l e c t r o n s , a t least i n non-anthrac i t ic and p o s s i b l y young a n t h r a c i t i c c o a l s , a r e a s s o c i a t e d wi th organic f r e e r a d i c a l s t r u c t u r e s . One group of i n v e s t i g a t o r s , however, has proposed t h a t charget ransfer complexes r a t h e r than s t a b l e f r e e r a d i c a l s may be r e s p o n s i b l e for the a b s o r p t i o n ( 6 ) .