Addition vs abstraction reactions of the methyl radical with nitrones, alkenes, aldehydes, and imines

In continuation of our theoretical study of spin trapping, we have compared the abilities of nitrones, imines, aldehydes, and alkenes to add the methy l radical vs their tendency to have protons abstracted by this radical. Thi s study confirms that for nitrones, whereas abstraction of the iminyl H is exothermic with a low activation energy, addition is even more favored, bot h thermodynamically and kinetically, with the addition occurring at the uns aturated carbon. For alkenes, the preferred process is also addition, but t he reactions are considerably less exothermic and have higher activation en ergy barriers than those for nitrones. Aldehydes favor abstraction; the bul kier the group on the carbonyl carbon, the more the abstraction is preferre d over addition. Imines are intermediate between alkenes and aldehydes in t heir tendency toward addition and abstraction. As a result, they can underg o either process, and the favored route entirely depends on the substituent s present; moreover, addition can occur to either the carbon or the nitroge n with appropriate substituents.