Is Williamson Ether Synthesis an SN1 or SN2 reaction?

First, it is necessary to understand the difference between an #S_N1# and an #S_N2# mechanism.

An SN1 mechanism is a two-step mechanism and racemization occurs:

1. Departures of the leaving group#->#formation of carbocation

2. Nucleophilic attack (usually a weak nucleophile) on carbocation#->#racemic product
   
   An SN2 mechanism is a concerted (one-step) mechanism:

3. Nucleophile attacks (strong nucleophile) from backside of leaving group #->#product has inverted stereochemistry
   

A Williamson Ether synthesis is carried out using an alcohol and an alkyl halide. First, the alcohol is deprotonated using a strong base to create an alkoxide anion as shown in the reaction below:

#ROH + B^-##rightleftharpoonsRO^-##+BH#

When the alkyl halide is added to the reaction, the alkoxide anion (#RO^(-)#) will act as a nucleophile and displace the halide connected to the electrophilic carbon in a concerted (one-step) reaction.

For example:

Note: The ether product will have opposite stereochemistry to the original alkyl halide at the electrophilic carbon