Is the tert-butyl chloride solvolysis the most misunderstood reaction in organic chemistry? Evidence against nucleophilic solvent participation in the tert-butyl chloride transition state and for increased hydrogen bond donation to the 1-adamantyl chloride solvolysis transition state

Despite theoretical calculations to the contrary, it has been argued that t he I-adamantyl cation is more stable than the tert-butyl cation in media of high dielectric constant. This argument has been utilized to suggest that the higher rate of solvolysis of tert-butyl chloride in aqueous ethanol is evidence for nucleophilic solvent participation in this classic reaction. F urther, in "more highly ionizing" solvents, the rate of 1-adamantyl chlorid e is nearly the same as that of tert-butyl chloride, which is interpreted a s a manifestation of the relative stabilities of the cations. However, the evidence cited does not explain the increased sensitivity of the rate of so lvolysis of 1-adamantyl chloride over tert-butyl chloride to solvents which are better able to donate hydrogen bonds. The hypothesis developed here is that 1-adamantyl chloride solvolysis is assisted by hydrogen bond donation departing chloride ion to a greater extent than that of tert-butyl chlorid e solvolysis, most likely due to lessened steric interactions in a developi ng pyramidal cation. This hypothesis is supported by multiparameter solvent effect factor analyses utilizing the KOMPH2 equation which, in addition, q uantifies the important role of ground-state destabilization due to strong solvent-solvent interactions. An important result from the good correlation of free energies of transfer of the tert-butyl chloride solvolysis transit ion state is that there is no change in mechanism, and, in particular, no n ucleophilic participation even in non-hydroxylic basic solvents. The equati on is also applied to the case of dimethylsulfonium. ion solvolyses where t he tert-butyl salt reacts substantially faster than the 1-adamantyl salt in ethanol and the gas phase. The decreased rate of the former in hydrogen bo nd donating solvents relative to the gas phase is as yet unclear. Solvent N values that were generated to characterize solvent nucleophilicity are sho wn not to be correlated by measures of solvent basicity but rather by the n egative of measures of solvent hydrogen bond donor ability.