EPR INVESTIGATIONS OF BETA-DEUTERIATED 5,5''-DIMETHYL-2,2' 5',2''-TERTHIOPHENES/

The unambiguous assignment of the beta-hyperfine coupling constants of the radical cations of 5,5''-dimethyl-2,2':5',2''-terthiophene (11) h as been achieved by EPR spectroscopic investigations of the deuteriate d compounds 12, 13 and 14. The syntheses of these substances were achi eved by cross-coupling following the Negishi and Kumada reaction start ing from deuteriated derivatives of chloromethylated thiophene derivat ives. The generation of the radical cations was carried out by electro chemical oxidation at a constant potential in the EPR spectrometer, In the presence of acidic compounds a D-H exchange at the beta-positions of oligothiophenes was observed, The experimentally determined spin d ensity distribution was rationalized by means of semiempirical quantum mechanical calculations (RHF-INDO-SP). Theoretical and experimental a ssignments are In good agreement.