The structure of amidyl radicals. Evidence for the \u3c0-electronic ground state and for twist about the acyl-nitrogen bond by electron paramagnetic resonance spectroscopy

The EPR spectroscopic parameters for a number of acyclic N-alkylcarboxamidyls, R\u1e44C(O)\u154, have been measured over a wide range of temperatures. The results can only be interpreted in terms of a \u3c0-electronic configuration in which the unpaired electron resides mainly in an N 2p orbital perpendicular to the RNC plane. Measurements of the 13C hyperfine splittings (hfs) for some R\u1e44C(O)13CH3 demonstrate that the O and 13C atoms lie in or near the RNC plane except when R is tert-butyl, in which case steric forces twist these atoms out of this plane by 20\ub0 or more. There is less conjugative delocalization of the unpaired electron from N to O in the Me3C\u1e44C(O)R\u2032 radicals because they are twisted and hence these radicals have a larger N hfs and a smaller g value than amidyls which have R = primary or secondary alkyl. The first cyclic amidyl, 5,5-dimethyl-2-oxopyrrolidin-1-yl, has been detected. This radical has a smaller N hfs (11.2 G) and a higher g value (2.0063) than the acyclic radicals. \ua9 1981 American Chemical Society.Peer reviewed: YesNRC publication: Ye