Although the addition of H-CN to an alkene could be envisioned to occur by a free-radical chain mechanism, such a reaction is not observed. Justify each of the following reasons with appropriate calculations using bond dissociation energies.
(a) The reaction of H-CN with initiating (CH3)3C-O' radicals is not a good source of 'CN radicals.
(b) The second propagation step of the free-radical addition is energetically unfavorable:

Transcribed Image Text:

RCHCHCN H-CNRCHCH2CN .CN