Two-Step Ionic Mechanisms The SN2-Si Pathway

Silylation of an alcohol, a common method for OH group protection in organic chemistry, typically involves such a mechanism  

The chloride leaves only in a second or later step, as shown below  

The overall two-step or multistep mechanism is often called as this process has been 

Certain carbon-heteroatom bonds may ionize, especially in polar protic media (sometimes referred to as solvolytic conditions), to generate carbocations. This is shown below for t-butyl tosylate in acetic acid  

This rate-determining D step forms the first step of both the S l and El pathways. In 1 (substitution, nucleophilic, unimolecular), the carbocation combines with a nucleophile, often derived from the solvent. In El, a base, again often derived from the solvent, depro-tonates the carbocation and generates an alkene. In this case, the nucleophile or base is the acetate anion (AcO )  

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