SOLVENT PRESSURE EFFECTS IN FREE-RADICAL REACTIONS .2. RECONCILIATIONOF THE GAS AND CONDENSED-PHASE CHLORINATION OF CYCLOPROPANE

The results reported herein demonstrate that the chemoselectivity (S(H )2 ring opening vs abstraction of a cyclopropyl hydrogen) associated w ith the free radical chlorination of cyclopropane is solvent dependent . Internal pressure is implicated as the solvent parameter responsible for the observed solvent effect. (Solvents of high internal pressure favor the S(H)2 process; hydrogen abstraction becomes more important i n solvents of low internal pressure or in the gas phase.) Extrapolatio n of the solution phase results to zero internal pressure accurately p redicts the gas-phase result, suggesting that the difference in chemos electivity between the vapor- and condensed-phase reactions is attribu table to internal pressure in the condensed phase medium. No evidence for the chlorine atom cage effect is found in the chlorination of cycl opropane.