Answer:
see answer
Explanation:
You are not providing the molecule, however, I found the same question on another place, and I realize that the compound you need is in picture 1. In order to do this by williamson synthesis, this reaction implies an alkyl bromide and an alcoxide. When this two reactants react, they undergo an Sn2 reaction, where the O- attacks the alkyl bromide, and the bromine leaves the molecule, therefore forming the ether desired.
Now we have two possibilities of this to occur.
1) using methoxide and a tertiary alkyl bromide.
2) using tertbutoxide and a primary alkyl bromide.
In possibility 1, the methoxide is a very strong base and instead of doing an sn2 reaction, it will undergo an E2 reaction, so the substitued product will not form.
In possibility 2, we will do a SN2 reaction cause the terbutoxide it's not a strong base, or at least it's not that strong as methoxide, so it can easily attack the primary alkyl bromide to form the methyl t-butyl ether.
See picture 2 for mechanism for both possibilities:
