The specific rates of solvolysis (including those obtained from the literature) of isopropenyl chloroformate (1) are analyzed using the extended Grunwald-Winstein equation, involving the NT scale of solvent nucleophilicity (S-methyldibenzothiophenium ion) combined with a YCl scale based on 1-adamantyl chloride solvolysis. A similarity model approach, using phenyl chloroformate solvolyses for comparison, indicated a dominant bimolecular carbonyl-addition mechanism for the solvolyses of 1 in all solvents except 97% 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP). An extensive evaluation of the outcomes acquired through the application of the extended Grunwald-Winstein equation resulted in the proposal of an addition-elimination mechanism dominating in most of the solvents, but in 97-70% HFIP, and 97% 2,2,2-trifluoroethanol (TFE), it is proposed that a superimposed unimolecular (SN1) type ionization is making a significant contribution.