Photolysis of N-nitrosamines in acidic acetonitrile produces aminium radical cations via protonation of the initially-formed aminyl radicals. The kinetics of these species can be monitored by transient UV spectroscopy via their absorption band which is found at ca. 300 nm in the case of the piperidinium radical, for example. By measuring the aminium radicals' lifetimes as a function of the concentration of added olefin, absolute values for the bimolecular rate constants for the addition reactions were obtained. In the case of the piperidinium radical, these rate constants varied from <1 × 106 M-1 s-1 for acrylonitrile to 1.1 ± 0.1 × 109 M-1 s-1 for 1,1-diphenylethylene and generally increased with decreasing ionization potential of the olefin, thus confirming the electrophilic nature of the piperidinium radical. The rate constants for analogous reactions of diethylaminium radicals were 1.5−25 times smaller indicating the importance of steric factors in aminium radical additions to olefins. The rate constant for the intramolecular 1,5-addition of the secondary aminium radical cation to an unactivated double bond is estimated to be ca. 1 × 106 s-1, but the intramolecular addition rate constant increases to >1 × 108 s-1 upon the phenyl substitution at the olefinic terminus.

The EPR spectra of seven partially fluorinated derivatives of methyl-, ethyl-, and isopropyl-C60 radicals have been studied. The equilibrium configuration of each was deduced from their proton and I9F hyperfine interactions. If one or more of the hydrogens of CH3Ca are replaced by CF3, F, or CH3, there is a competition among them for the position over the pentagon adjacent to the c-c60 bond. The order CF3 > F > H > CH3 follows closely their respective inductive effect parameters 01. Quantum chemical calculations at the INDO/ UHF level have been used to rationalize this hierarchy in terms of charge separation on the c 6 0 surface.

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The EPR spectra of alkyl-and fluoroalkyl-C,, radicals are described and discussed. These radicals are of the general type XYZC-C,,, where X, Y and 2 are CF3, F, H or CH3. It is shown that there is a competition among X, Y and Z for the pentagon position adjacent to the C-C,, bond, and that in any given radical this position is gained by the most electronegative of them. Thus, if X, Y, Z is the order of decreasing electronegativity in the above sequence, X will occupy the pentagon position. If Y = X, the equilibrium conformation is asymmetric, with one X over the pentagon and the other over one of the hexagons. This conformation exchanges with its enantiomer above -200 K. An explanation based on quantum-chemical calculations of charge distribution on the C,,, surface indicates that the more electronegative ligands are attracted to regions of more positive charge over the pentagon.