[en] The solvolyses of the isopropenyl chloroformate proceeded rather rapidly at 35.0 .deg. C and the progress of the reaction as a function of time can be conveniently monitored using a rapid-response conductivity technique. For five typical solvents, the activation parameters were determined and the large negative entropies of activation were consistent with a bimolecular process. Application of the extended Grunwald-Winstein equation (equation 2) in 33 solvents led to an l value of 1.42 and an m value of 0.46 (correlation coefficient of 0.949). These values are shown to be similar to the previously determined values for a mechanism involving rate-limiting addition in an addition-elimination pathway. The kinetic solvent isotope effect is also very close to the literature values for the solvolyses of other chloroformate esters and it is consistent with general-base catalysis being super imposed upon a bimolecular process. The mechanism of acyl-transfer reactions have been investigated intensively for many years both experimentally and theoretically. The mechanisms of most of these reactions are, however, still not well established. The bimolecular solvolysis of acyl halides (RCOX) is believed to proceed either through a direct displacement mechanism (S_N2) or through an associative addition-elimination mechanism involving a tetrahedral intermediate. For acyl halides with a strong electron donating group, a dissociative mechanism involving an acylium ion intermediate has also been invoked. The two types of mechanism, S_N2 and stepwise addition-elimination, are also common for the bimolecular aminolysis of acyl halides. The aminolyses of acetyl chloride, MeCOCl, and methyl chloroformate, MeOCOCl, have been proposed to proceed by rate-limiting breakdown of a zwitterionic tetrahedral intermediate, T^±, for weakly basic amines with a change to rate-limiting attack for more basic amines