Radical cations of trialkylamines: ESR spectra and structures

Novel syntheses of cyclopropyldiisopropylamine (15), di-tert-butylcycloprop ylamine (16), dicyclopropylisopropylamine (17), and tricyclopropylamine (18 ) are described. Hyperfine data were determined by ESR spectroscopy for the radical cations of these trialkylamines, as well as for those of ethyldiis opropylamine (10), diisopropyl-n-propylamine (11), dicyclohexylethylamine ( 12), diisopropyl-3-pentylamine (14), and 1-azabicyclo[3.3.3]undecane (manxi ne; 27). The radical cation of triisopropylamine (13) was reexamined under conditions of improved spectral resolution. Coupling constants of the N-14 nucleus and the beta-protons in the radical cations of 18 trialkylamines pr ovide reliable information about the geometries of these species, which are confirmed by theoretical calculations. With the exception of a few oligocy clic amines, for which flattening is impaired by the rigid molecular framew ork, all of the radical cations should be planar. Correlation between the o bserved coupling constants of the beta-protons and the calculated <cos(2) t heta> values of the dihedral angle theta, defining the conformation of the alkyl substituent or the azacycloalkane, is verified. Upon oxidation, strik ing changes occur for those amines that have cyclopropyl substituents, beca use of the tendency of these groups to assume a perpendicular conformation in the neutral amines and a bisected orientation in the corresponding radic al cations.