EPR detection of three pentylthymines γ-irradiated at 77 K showed the production of a 5, 6- dihydro-5-thymyl radical (5-thymyl radical) as an H-addition radical and a secondary alkyl radical formed by C–H bond fission at the second carbon from the end of the pentyl group. The introduction of the pentyl group into thymine increased total radical yields at 77 K up to about twice that of thymine and considerably enhanced 5-thymyl radical yields. Several ...