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| - Evidence for Different Types of Water Participation in theSolvolysis of 1-Adamantyl, tert-Butyl, and Methyl Chlorides fromDensity Functional Theory Computations
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| - The activation energy in the gas phase (ΔE⧧) and the free energy of activation (ΔG⧧) in water solutionfor the hydrolysis of the monohydrates of methyl chloride (MeCl), tert-butyl chloride (t-BuCl), and1-adamantyl chloride (AdCl) have been computed with the B3LYP/631-G(d) method and thepolarizable continuum (PCM) solvation model. There is a fair agreement between the ΔG⧧ valuescomputed by us and the experimental data. The mechanistic implications of our computations arein severe contradiction with conventional representations. Thus, the computed nucleophilic solventassistance (NSA) for the backside attack of a water molecule in the hydrolysis of MeCl is slightlylower than the corresponding NSA for t-BuCl. Hence, the hydrolysis of both MeCl and t-BuCl takesplace mainly according to the classical SN2 mechanism. The most relevant difference is that ΔG⧧for the frontside attack of water to t-BuCl is disfavored only by ca. 2 kcal/mol with regard to thebackside attack but by ca. 23 kcal/mol in the case of MeCl. The higher solvolysis rate in water oft-BuCl in relation to AdCl is not due to steric factors affecting the specific solvation of thecorresponding transition states, but to differential bulk solvent effects, which are accounted for bythe PCM model.
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