Solvent Effects
See also: Solvent effectsSince the SN1 reaction involves formation of an unstable carbocation intermediate in the rate-determining step, anything that can facilitate this will speed up the reaction. The normal solvents of choice are both polar (to stabilize ionic intermediates in general) and protic (to solvate the leaving group in particular). Typical polar protic solvents include water and alcohols, which will also act as nucleophiles and the process is known as solvolysis.
The Y scale correlates solvolysis reaction rates of any solvent (k) with that of a standard solvent (80% v/v ethanol/water) (k0) through
with m a reactant constant (m = 1 for tert-butyl chloride) and Y a solvent parameter. For example 100% ethanol gives Y = −2.3, 50% ethanol in water Y = +1.65 and 15% concentration Y = +3.2.
Read more about this topic: SN1 Reaction
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