Long-Lived Trialkylamine Radical Cations Containing Cα-H Bonds in Acyclic Alkyl Groups

Article abstract of DOI:10.1021/jo00220a005

Chemical reversibility is observed in the cyclic voltammogram of 9-neopentyl-9-azabicyclo<3.3.1>nonane (3), allowing measurement of its E^o' value, 0.83 V vs.SCE in acetonitrile.Replacement of the tert-butyl group of 3 by isopropyl or phenyl leads to a much shorter radical cation lifetime, and E^o' could not be reliably measured for the 9-isobutyl or 9-benzyl compounds 6 or 7.The barrier for nitrogen inversion of 3, which must be accompanied by NCH2 rotation, is 12.0 kcal/mol at -10 deg C, 5 kcal/mol higher than the barrier for its 9-ethyl analogue 9.The dihedral angle between C_α-H and the nitrogen p orbital axis in the cation radical is argued to be important in determining cation radical lifetime.Observation of chemical reversibility in the CV of 9-(2-adamantyl)-9-azabicyclo<3.3.1>nonane, 5,required in situ drying of the solvent with alumina, as well as fast scan rates or low temperatures.