SOLVENT EFFECTS IN ELECTRONEUTRAL REACTIONS .I. COMBINATION AND DISPROPORTIONATION OF ETHYL RADICALS IN SOLUTION

The rate ratio kdkc of the disproportionation-combination reaction couple of ethyl radicals was measured at 65° in ten different solvents. The logarithms of these ratios are linear functions of the square root of the cohesive energy density of the solvents. The reaction couple was investigated in the gas phase from —65 to +80° in vessels of variable volume, and it was found that a considerable extent of the reaction proceeds by a heterogeneous mechanism. On the basis of these observations the temperature dependence of kd/kc in liquid and in solid reaction media is interpreted to be a consequence of a secondary thermal effect whose origin is the internal volume change of the medium. The rates of certain other polar reactions are discussed in terms of internal volume considerations. © 1968, American Chemical Society. All rights reserved.