Electron affinities of a homologous series of tertiary alkyl radicals and their C–H bond dissociation energies (BDEs)

Heats of formation have been derived from G3(MP2)//B3LYP and G3MP2B3(+) atomization energies for tert-butyl radical (6R), cubyl radical, bicyclooctyl radical (1R), and tricyclo[3.3.n.03,7]alk-3(7)-yl (n=0–3, 2R–5R) radicals, and their respective anions (1A–6A) and hydrocarbons (1H–6H). The electron affinity (EA) of 6R is estimated at 1.5±2 kcal/mol and tert-butyl anion (6A) is likely to be bound. In the homologous series 2R–5R the EAs range from 3.4±2 to 13.5±2 kcal/mol. The computed enthalpies of the acidities of the tricyclic hydrocarbons 1H–5H are in the range 407–411 kcal/mol. Their C–H bond dissociation energies (BDEs) are in the range 97–110 kcal/mol. The increase of the BDEs in the homologous series 2H–5H and the increase of EAs of 2A–5A is attributed to the enhanced pyramidalization induced in radicals 2R–5R by the shortening of the methylene chain connecting carbons C3 and C7.