SOLVENT EFFECTS IN THE REACTIONS OF FREE RADICALS AND ATOMS¹

Kinetics and Mechanism of the Gas-Phase Reaction of Cl Atoms and OH Radicals with Fluorobenzene at 296 K

“…In solution phase studies, it has been observed that Cl atoms add to the aromatic ring with rate constants which are close to the diffusion limit. [10][11][12][13][14][15][16][17] Such observations suggest that reaction 5b proceeds with a rate constant of the order of 10 -10 cm 3 molecule -1 s -1 in the gas phase. Proceeding on this assumption leads to an estimate of k -5b ) 9 × 10 7 s -1 .…”

The Inhibited Autoxidation of Styrene: Part Ii. The Relative Inhibiting Efficiencies of Meta- And Para-Substituted Phenols

“…A change in p produced by a change in solvent might be due either to a change in the polarizability of the solvent or to a complexing of the radicals with the solvent, particularly if it is arolnatic (27). I t is difficult to evaluate the importance of the first factor from reactions [5] and [6] since benzene and CC14 have very similar polarizabilities.…”

“…If the radical complexes with the solvent one rnight expect a decreased sensitivity t o polar effects, i.e., a decreased p, since polarization in the same direction will be involved in the complex as in the transition state. The overall reactivity of the radical will, of course, also be decreased by complexing-, However, solvent effects must also depend on the nature of the attacking radical and reactant since, for reaction [12], p is the same in benzene as in CC14 even though chlorine atoms are known t o complex with aromatic solvents (27). The possible importance of solvent effects suggests that p values obtained by competitive experiments in mixed reactants are less valuable than those obtained in a pure solvent since the polarizability of the medium will change as the reactants are changed.…”

THE EFFECT OF SUBSTITUENTS ON THE RELATIVE RATES OF REACTION OF tert-BUTOXY RADICALS WITH PHENOLS IN CARBON TETRACHLORIDE AND IN CHLOROBENZENE

“…By analogy to a similar, but much larger,$ effect which has been observed with chlorine atoms (25,26) concluded that a rr complex is formed between the t-butoxy radical and the aromatic T electrons. The complexed radical is apparently less reactive and it therefore tends to decompose rather than to abstract hydrogen.…”