ESR Study of 2-Substituted 2-Adamantyl Radicals. Configuration and Long-Range Hyperfine Interaction.

Article abstract of DOI:10.1021/ja00203a029

Structure and long-range hyperfine interaction in 2-adamantyl, 5,7-dimethyl-2-adamantyl, and the various 2-substituted radicals (substituent = CH3, CH2SiMe3, OSiMe3, SSiMe3, CH2GeMe3, etc.) were studied by ESR.The origin of the long-range hyperfine interaction is discussed on the basis of the comparison between experimental and theoretical hfs values.The pyramidality of the radical center by a proper substituent at the 2-position of 2-adamantyl radicals has been found to exert significant influence to the long-range interaction.The analyses of hfs values for persistent 2-bis( trimethylsilyl)methyl-2-adamantyl radical and the 5,7-dimethyl derivative were made by the assistance of the ENDOR spectrum.The very small hfs values observed for the bis(trimethylsilyl)methyl methine protons not only show almost perpendicular arrangement of the Cα-Hβ bond to the singly occupied p? orbital but also suggest that the constant A in the Heller-McConnell equation would be positive on the basis of the positive temperature dependence.