Kinetic applications of electron paramagnetic resonance spectroscopy. XX. 2,4,6-Tri(tert-butyl)benzyl, -anilino, -phenoxy, and -phenylthiyl radicals

The title radicals have been generated, and their kinetic behavior has been examined. The EPR parameters for the benzyl and anilino radicals indicate that the benzylic and amino hydrogens are coplanar with the aromatic rings. The benzyl radical decays rapidly with second-order kinetics (k = (5 \ub1 2) 7 108 M-1 sec-1 at 24\ub0) to give the bibenzyl. The anilino radical exists in equilibrium with the hydrazine (\u394H = -13.1 \ub1 0.5 kcal/mol, \u394S = -27 \ub1 2 gibbs/mol). The rate constant for anilino decay to its dimer can be represented by log (k-1/M-1 sec-1) = 6.3(\ub11.0) - 2.5(\ub10.8)/\u3b8, where \u3b8 = 2.3RT kcal/mol, and that for decomposition of dimer to two anilino radicals by log (k1/sec-1) = 12.2 - 15.6/\u3b8. The phenylthiyl radical is also in equilibrium with its dimer at ambient temperatures (\u394H = -23.3 kcal/mol), but the phenoxy radical shows no sign of dimerization even at -100\ub0. The behavior of these four radicals is discussed in terms of the strengths of the bonds formed by head-to-head dimerization.Peer reviewed: YesNRC publication: Ye