The radicals produced from 2-methylfuran, 2,5-dimethylfuran, 2-methylthiophene, 3-methylthiophene, and 2,5-dimethylthiophene via H-atom abstraction initiated by tert-butoxy radicals (produced by photolysis of di-tert-butyl peroxide) in the liquid phase have been examined by X-band electron paramagnetic resonance spectrometry. Hyperfine splitting constants for all five radicals have been determined, and assigned to corresponding radical structures. In all cases, H-atom abstraction occurred at the methyl group attached to the furan or thiophene moiety. In the case of 3-methylthiophene, a controversy concerning assignment of hfsc values to positions 4 and 5 that was evident from previous literature reports has been satisfactorily resolved by deuterating 3-methylthiophene at position 5 and examining the resultant radical produced by EPR. © 1980.