The reaction pathway for the 2H(2)O + CCl2 reaction through a cyclic five-atom transition structure was studied using ab initio molecular orbital theory. The MP2 method in conjunction with the DZP basis set was used for geometry optimizations, and single point energy calculations were performed at MP2 and MP4 levels with the cc-pVDZ and cc-pVTZ basis sets. The solvent effect on the activation free energy was evaluated by Monte Carlo statistical mechanics calculations. The new mechanism has a high rate constant, and we predict a lifetime of seven nanoseconds for dichlorocarbene in aqueous solution. We have proposed that this mechanism occurs for the reaction of dichlorocarbene with water, and possibly may be involved in many reactions of carbenes with alcohols. We have also shown that it can explain the following experimental facts: (a) alteration of the product isotopic effect on addition of a second alcohol, (b) difference between product and kinetic isotopic effects, and (c) no linear dependence of the observed rate constant for carbene decay on alcohol concentration.