Sels d'atdp—20 : Relations reactivite-structure dans les cinetiques de decomposition de sels d'atdp substitues. hypersensibilite a des substituants en position 3 de la

The kinetics of decomposition of various propyloxy phosphonium chlorides, the chain of which is substituted with non polar groups in position 2 and polar groups in position 3, have been measured in pyridine and in DMF. The validity of Taft correlation with σ^* parameters have been ascertained within each of the three linear, branched and neopentylic series, using Exner's criterion. In both solvents, it appeared that the sensitivity parameter ?^* for the neopentylic series varies considerably with the temperature and may reach unusually high values. This phenomenon is interpreted by a proximity effect between the substituent and the seat of the reaction, due to steric constraints.